| 1 | /* |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * All rights reserved. |
| 4 | * |
| 5 | * This source code is licensed under both the BSD-style license (found in the |
| 6 | * LICENSE file in the root directory of this source tree) and the GPLv2 (found |
| 7 | * in the COPYING file in the root directory of this source tree). |
| 8 | * You may select, at your option, one of the above-listed licenses. |
| 9 | */ |
| 10 | |
| 11 | /// Zstandard educational decoder implementation |
| 12 | /// See https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md |
| 13 | |
| 14 | #include <stdint.h> // uint8_t, etc. |
| 15 | #include <stdlib.h> // malloc, free, exit |
| 16 | #include <stdio.h> // fprintf |
| 17 | #include <string.h> // memset, memcpy |
| 18 | #include "zstd_decompress.h" |
| 19 | |
| 20 | |
| 21 | /******* IMPORTANT CONSTANTS *********************************************/ |
| 22 | |
| 23 | // Zstandard frame |
| 24 | // "Magic_Number |
| 25 | // 4 Bytes, little-endian format. Value : 0xFD2FB528" |
| 26 | #define ZSTD_MAGIC_NUMBER 0xFD2FB528U |
| 27 | |
| 28 | // The size of `Block_Content` is limited by `Block_Maximum_Size`, |
| 29 | #define ZSTD_BLOCK_SIZE_MAX ((size_t)128 * 1024) |
| 30 | |
| 31 | // literal blocks can't be larger than their block |
| 32 | #define MAX_LITERALS_SIZE ZSTD_BLOCK_SIZE_MAX |
| 33 | |
| 34 | |
| 35 | /******* UTILITY MACROS AND TYPES *********************************************/ |
| 36 | #define MAX(a, b) ((a) > (b) ? (a) : (b)) |
| 37 | #define MIN(a, b) ((a) < (b) ? (a) : (b)) |
| 38 | |
| 39 | #if defined(ZDEC_NO_MESSAGE) |
| 40 | #define MESSAGE(...) |
| 41 | #else |
| 42 | #define MESSAGE(...) fprintf(stderr, "" __VA_ARGS__) |
| 43 | #endif |
| 44 | |
| 45 | /// This decoder calls exit(1) when it encounters an error, however a production |
| 46 | /// library should propagate error codes |
| 47 | #define ERROR(s) \ |
| 48 | do { \ |
| 49 | MESSAGE("Error: %s\n", s); \ |
| 50 | exit(1); \ |
| 51 | } while (0) |
| 52 | #define INP_SIZE() \ |
| 53 | ERROR("Input buffer smaller than it should be or input is " \ |
| 54 | "corrupted") |
| 55 | #define OUT_SIZE() ERROR("Output buffer too small for output") |
| 56 | #define CORRUPTION() ERROR("Corruption detected while decompressing") |
| 57 | #define BAD_ALLOC() ERROR("Memory allocation error") |
| 58 | #define IMPOSSIBLE() ERROR("An impossibility has occurred") |
| 59 | |
| 60 | typedef uint8_t u8; |
| 61 | typedef uint16_t u16; |
| 62 | typedef uint32_t u32; |
| 63 | typedef uint64_t u64; |
| 64 | |
| 65 | typedef int8_t i8; |
| 66 | typedef int16_t i16; |
| 67 | typedef int32_t i32; |
| 68 | typedef int64_t i64; |
| 69 | /******* END UTILITY MACROS AND TYPES *****************************************/ |
| 70 | |
| 71 | /******* IMPLEMENTATION PRIMITIVE PROTOTYPES **********************************/ |
| 72 | /// The implementations for these functions can be found at the bottom of this |
| 73 | /// file. They implement low-level functionality needed for the higher level |
| 74 | /// decompression functions. |
| 75 | |
| 76 | /*** IO STREAM OPERATIONS *************/ |
| 77 | |
| 78 | /// ostream_t/istream_t are used to wrap the pointers/length data passed into |
| 79 | /// ZSTD_decompress, so that all IO operations are safely bounds checked |
| 80 | /// They are written/read forward, and reads are treated as little-endian |
| 81 | /// They should be used opaquely to ensure safety |
| 82 | typedef struct { |
| 83 | u8 *ptr; |
| 84 | size_t len; |
| 85 | } ostream_t; |
| 86 | |
| 87 | typedef struct { |
| 88 | const u8 *ptr; |
| 89 | size_t len; |
| 90 | |
| 91 | // Input often reads a few bits at a time, so maintain an internal offset |
| 92 | int bit_offset; |
| 93 | } istream_t; |
| 94 | |
| 95 | /// The following two functions are the only ones that allow the istream to be |
| 96 | /// non-byte aligned |
| 97 | |
| 98 | /// Reads `num` bits from a bitstream, and updates the internal offset |
| 99 | static inline u64 IO_read_bits(istream_t *const in, const int num_bits); |
| 100 | /// Backs-up the stream by `num` bits so they can be read again |
| 101 | static inline void IO_rewind_bits(istream_t *const in, const int num_bits); |
| 102 | /// If the remaining bits in a byte will be unused, advance to the end of the |
| 103 | /// byte |
| 104 | static inline void IO_align_stream(istream_t *const in); |
| 105 | |
| 106 | /// Write the given byte into the output stream |
| 107 | static inline void IO_write_byte(ostream_t *const out, u8 symb); |
| 108 | |
| 109 | /// Returns the number of bytes left to be read in this stream. The stream must |
| 110 | /// be byte aligned. |
| 111 | static inline size_t IO_istream_len(const istream_t *const in); |
| 112 | |
| 113 | /// Advances the stream by `len` bytes, and returns a pointer to the chunk that |
| 114 | /// was skipped. The stream must be byte aligned. |
| 115 | static inline const u8 *IO_get_read_ptr(istream_t *const in, size_t len); |
| 116 | /// Advances the stream by `len` bytes, and returns a pointer to the chunk that |
| 117 | /// was skipped so it can be written to. |
| 118 | static inline u8 *IO_get_write_ptr(ostream_t *const out, size_t len); |
| 119 | |
| 120 | /// Advance the inner state by `len` bytes. The stream must be byte aligned. |
| 121 | static inline void IO_advance_input(istream_t *const in, size_t len); |
| 122 | |
| 123 | /// Returns an `ostream_t` constructed from the given pointer and length. |
| 124 | static inline ostream_t IO_make_ostream(u8 *out, size_t len); |
| 125 | /// Returns an `istream_t` constructed from the given pointer and length. |
| 126 | static inline istream_t IO_make_istream(const u8 *in, size_t len); |
| 127 | |
| 128 | /// Returns an `istream_t` with the same base as `in`, and length `len`. |
| 129 | /// Then, advance `in` to account for the consumed bytes. |
| 130 | /// `in` must be byte aligned. |
| 131 | static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len); |
| 132 | /*** END IO STREAM OPERATIONS *********/ |
| 133 | |
| 134 | /*** BITSTREAM OPERATIONS *************/ |
| 135 | /// Read `num` bits (up to 64) from `src + offset`, where `offset` is in bits, |
| 136 | /// and return them interpreted as a little-endian unsigned integer. |
| 137 | static inline u64 read_bits_LE(const u8 *src, const int num_bits, |
| 138 | const size_t offset); |
| 139 | |
| 140 | /// Read bits from the end of a HUF or FSE bitstream. `offset` is in bits, so |
| 141 | /// it updates `offset` to `offset - bits`, and then reads `bits` bits from |
| 142 | /// `src + offset`. If the offset becomes negative, the extra bits at the |
| 143 | /// bottom are filled in with `0` bits instead of reading from before `src`. |
| 144 | static inline u64 STREAM_read_bits(const u8 *src, const int bits, |
| 145 | i64 *const offset); |
| 146 | /*** END BITSTREAM OPERATIONS *********/ |
| 147 | |
| 148 | /*** BIT COUNTING OPERATIONS **********/ |
| 149 | /// Returns the index of the highest set bit in `num`, or `-1` if `num == 0` |
| 150 | static inline int highest_set_bit(const u64 num); |
| 151 | /*** END BIT COUNTING OPERATIONS ******/ |
| 152 | |
| 153 | /*** HUFFMAN PRIMITIVES ***************/ |
| 154 | // Table decode method uses exponential memory, so we need to limit depth |
| 155 | #define HUF_MAX_BITS (16) |
| 156 | |
| 157 | // Limit the maximum number of symbols to 256 so we can store a symbol in a byte |
| 158 | #define HUF_MAX_SYMBS (256) |
| 159 | |
| 160 | /// Structure containing all tables necessary for efficient Huffman decoding |
| 161 | typedef struct { |
| 162 | u8 *symbols; |
| 163 | u8 *num_bits; |
| 164 | int max_bits; |
| 165 | } HUF_dtable; |
| 166 | |
| 167 | /// Decode a single symbol and read in enough bits to refresh the state |
| 168 | static inline u8 HUF_decode_symbol(const HUF_dtable *const dtable, |
| 169 | u16 *const state, const u8 *const src, |
| 170 | i64 *const offset); |
| 171 | /// Read in a full state's worth of bits to initialize it |
| 172 | static inline void HUF_init_state(const HUF_dtable *const dtable, |
| 173 | u16 *const state, const u8 *const src, |
| 174 | i64 *const offset); |
| 175 | |
| 176 | /// Decompresses a single Huffman stream, returns the number of bytes decoded. |
| 177 | /// `src_len` must be the exact length of the Huffman-coded block. |
| 178 | static size_t HUF_decompress_1stream(const HUF_dtable *const dtable, |
| 179 | ostream_t *const out, istream_t *const in); |
| 180 | /// Same as previous but decodes 4 streams, formatted as in the Zstandard |
| 181 | /// specification. |
| 182 | /// `src_len` must be the exact length of the Huffman-coded block. |
| 183 | static size_t HUF_decompress_4stream(const HUF_dtable *const dtable, |
| 184 | ostream_t *const out, istream_t *const in); |
| 185 | |
| 186 | /// Initialize a Huffman decoding table using the table of bit counts provided |
| 187 | static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, |
| 188 | const int num_symbs); |
| 189 | /// Initialize a Huffman decoding table using the table of weights provided |
| 190 | /// Weights follow the definition provided in the Zstandard specification |
| 191 | static void HUF_init_dtable_usingweights(HUF_dtable *const table, |
| 192 | const u8 *const weights, |
| 193 | const int num_symbs); |
| 194 | |
| 195 | /// Free the malloc'ed parts of a decoding table |
| 196 | static void HUF_free_dtable(HUF_dtable *const dtable); |
| 197 | /*** END HUFFMAN PRIMITIVES ***********/ |
| 198 | |
| 199 | /*** FSE PRIMITIVES *******************/ |
| 200 | /// For more description of FSE see |
| 201 | /// https://github.com/Cyan4973/FiniteStateEntropy/ |
| 202 | |
| 203 | // FSE table decoding uses exponential memory, so limit the maximum accuracy |
| 204 | #define FSE_MAX_ACCURACY_LOG (15) |
| 205 | // Limit the maximum number of symbols so they can be stored in a single byte |
| 206 | #define FSE_MAX_SYMBS (256) |
| 207 | |
| 208 | /// The tables needed to decode FSE encoded streams |
| 209 | typedef struct { |
| 210 | u8 *symbols; |
| 211 | u8 *num_bits; |
| 212 | u16 *new_state_base; |
| 213 | int accuracy_log; |
| 214 | } FSE_dtable; |
| 215 | |
| 216 | /// Return the symbol for the current state |
| 217 | static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, |
| 218 | const u16 state); |
| 219 | /// Read the number of bits necessary to update state, update, and shift offset |
| 220 | /// back to reflect the bits read |
| 221 | static inline void FSE_update_state(const FSE_dtable *const dtable, |
| 222 | u16 *const state, const u8 *const src, |
| 223 | i64 *const offset); |
| 224 | |
| 225 | /// Combine peek and update: decode a symbol and update the state |
| 226 | static inline u8 FSE_decode_symbol(const FSE_dtable *const dtable, |
| 227 | u16 *const state, const u8 *const src, |
| 228 | i64 *const offset); |
| 229 | |
| 230 | /// Read bits from the stream to initialize the state and shift offset back |
| 231 | static inline void FSE_init_state(const FSE_dtable *const dtable, |
| 232 | u16 *const state, const u8 *const src, |
| 233 | i64 *const offset); |
| 234 | |
| 235 | /// Decompress two interleaved bitstreams (e.g. compressed Huffman weights) |
| 236 | /// using an FSE decoding table. `src_len` must be the exact length of the |
| 237 | /// block. |
| 238 | static size_t FSE_decompress_interleaved2(const FSE_dtable *const dtable, |
| 239 | ostream_t *const out, |
| 240 | istream_t *const in); |
| 241 | |
| 242 | /// Initialize a decoding table using normalized frequencies. |
| 243 | static void FSE_init_dtable(FSE_dtable *const dtable, |
| 244 | const i16 *const norm_freqs, const int num_symbs, |
| 245 | const int accuracy_log); |
| 246 | |
| 247 | /// Decode an FSE header as defined in the Zstandard format specification and |
| 248 | /// use the decoded frequencies to initialize a decoding table. |
| 249 | static void FSE_decode_header(FSE_dtable *const dtable, istream_t *const in, |
| 250 | const int max_accuracy_log); |
| 251 | |
| 252 | /// Initialize an FSE table that will always return the same symbol and consume |
| 253 | /// 0 bits per symbol, to be used for RLE mode in sequence commands |
| 254 | static void FSE_init_dtable_rle(FSE_dtable *const dtable, const u8 symb); |
| 255 | |
| 256 | /// Free the malloc'ed parts of a decoding table |
| 257 | static void FSE_free_dtable(FSE_dtable *const dtable); |
| 258 | /*** END FSE PRIMITIVES ***************/ |
| 259 | |
| 260 | /******* END IMPLEMENTATION PRIMITIVE PROTOTYPES ******************************/ |
| 261 | |
| 262 | /******* ZSTD HELPER STRUCTS AND PROTOTYPES ***********************************/ |
| 263 | |
| 264 | /// A small structure that can be reused in various places that need to access |
| 265 | /// frame header information |
| 266 | typedef struct { |
| 267 | // The size of window that we need to be able to contiguously store for |
| 268 | // references |
| 269 | size_t window_size; |
| 270 | // The total output size of this compressed frame |
| 271 | size_t frame_content_size; |
| 272 | |
| 273 | // The dictionary id if this frame uses one |
| 274 | u32 dictionary_id; |
| 275 | |
| 276 | // Whether or not the content of this frame has a checksum |
| 277 | int content_checksum_flag; |
| 278 | // Whether or not the output for this frame is in a single segment |
| 279 | int single_segment_flag; |
| 280 | } frame_header_t; |
| 281 | |
| 282 | /// The context needed to decode blocks in a frame |
| 283 | typedef struct { |
| 284 | frame_header_t header; |
| 285 | |
| 286 | // The total amount of data available for backreferences, to determine if an |
| 287 | // offset too large to be correct |
| 288 | size_t current_total_output; |
| 289 | |
| 290 | const u8 *dict_content; |
| 291 | size_t dict_content_len; |
| 292 | |
| 293 | // Entropy encoding tables so they can be repeated by future blocks instead |
| 294 | // of retransmitting |
| 295 | HUF_dtable literals_dtable; |
| 296 | FSE_dtable ll_dtable; |
| 297 | FSE_dtable ml_dtable; |
| 298 | FSE_dtable of_dtable; |
| 299 | |
| 300 | // The last 3 offsets for the special "repeat offsets". |
| 301 | u64 previous_offsets[3]; |
| 302 | } frame_context_t; |
| 303 | |
| 304 | /// The decoded contents of a dictionary so that it doesn't have to be repeated |
| 305 | /// for each frame that uses it |
| 306 | struct dictionary_s { |
| 307 | // Entropy tables |
| 308 | HUF_dtable literals_dtable; |
| 309 | FSE_dtable ll_dtable; |
| 310 | FSE_dtable ml_dtable; |
| 311 | FSE_dtable of_dtable; |
| 312 | |
| 313 | // Raw content for backreferences |
| 314 | u8 *content; |
| 315 | size_t content_size; |
| 316 | |
| 317 | // Offset history to prepopulate the frame's history |
| 318 | u64 previous_offsets[3]; |
| 319 | |
| 320 | u32 dictionary_id; |
| 321 | }; |
| 322 | |
| 323 | /// A tuple containing the parts necessary to decode and execute a ZSTD sequence |
| 324 | /// command |
| 325 | typedef struct { |
| 326 | u32 literal_length; |
| 327 | u32 match_length; |
| 328 | u32 offset; |
| 329 | } sequence_command_t; |
| 330 | |
| 331 | /// The decoder works top-down, starting at the high level like Zstd frames, and |
| 332 | /// working down to lower more technical levels such as blocks, literals, and |
| 333 | /// sequences. The high-level functions roughly follow the outline of the |
| 334 | /// format specification: |
| 335 | /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md |
| 336 | |
| 337 | /// Before the implementation of each high-level function declared here, the |
| 338 | /// prototypes for their helper functions are defined and explained |
| 339 | |
| 340 | /// Decode a single Zstd frame, or error if the input is not a valid frame. |
| 341 | /// Accepts a dict argument, which may be NULL indicating no dictionary. |
| 342 | /// See |
| 343 | /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame-concatenation |
| 344 | static void decode_frame(ostream_t *const out, istream_t *const in, |
| 345 | const dictionary_t *const dict); |
| 346 | |
| 347 | // Decode data in a compressed block |
| 348 | static void decompress_block(frame_context_t *const ctx, ostream_t *const out, |
| 349 | istream_t *const in); |
| 350 | |
| 351 | // Decode the literals section of a block |
| 352 | static size_t decode_literals(frame_context_t *const ctx, istream_t *const in, |
| 353 | u8 **const literals); |
| 354 | |
| 355 | // Decode the sequences part of a block |
| 356 | static size_t decode_sequences(frame_context_t *const ctx, istream_t *const in, |
| 357 | sequence_command_t **const sequences); |
| 358 | |
| 359 | // Execute the decoded sequences on the literals block |
| 360 | static void execute_sequences(frame_context_t *const ctx, ostream_t *const out, |
| 361 | const u8 *const literals, |
| 362 | const size_t literals_len, |
| 363 | const sequence_command_t *const sequences, |
| 364 | const size_t num_sequences); |
| 365 | |
| 366 | // Copies literals and returns the total literal length that was copied |
| 367 | static u32 copy_literals(const size_t seq, istream_t *litstream, |
| 368 | ostream_t *const out); |
| 369 | |
| 370 | // Given an offset code from a sequence command (either an actual offset value |
| 371 | // or an index for previous offset), computes the correct offset and updates |
| 372 | // the offset history |
| 373 | static size_t compute_offset(sequence_command_t seq, u64 *const offset_hist); |
| 374 | |
| 375 | // Given an offset, match length, and total output, as well as the frame |
| 376 | // context for the dictionary, determines if the dictionary is used and |
| 377 | // executes the copy operation |
| 378 | static void execute_match_copy(frame_context_t *const ctx, size_t offset, |
| 379 | size_t match_length, size_t total_output, |
| 380 | ostream_t *const out); |
| 381 | |
| 382 | /******* END ZSTD HELPER STRUCTS AND PROTOTYPES *******************************/ |
| 383 | |
| 384 | size_t ZSTD_decompress(void *const dst, const size_t dst_len, |
| 385 | const void *const src, const size_t src_len) { |
| 386 | dictionary_t* const uninit_dict = create_dictionary(); |
| 387 | size_t const decomp_size = ZSTD_decompress_with_dict(dst, dst_len, src, |
| 388 | src_len, uninit_dict); |
| 389 | free_dictionary(uninit_dict); |
| 390 | return decomp_size; |
| 391 | } |
| 392 | |
| 393 | size_t ZSTD_decompress_with_dict(void *const dst, const size_t dst_len, |
| 394 | const void *const src, const size_t src_len, |
| 395 | dictionary_t* parsed_dict) { |
| 396 | |
| 397 | istream_t in = IO_make_istream(src, src_len); |
| 398 | ostream_t out = IO_make_ostream(dst, dst_len); |
| 399 | |
| 400 | // "A content compressed by Zstandard is transformed into a Zstandard frame. |
| 401 | // Multiple frames can be appended into a single file or stream. A frame is |
| 402 | // totally independent, has a defined beginning and end, and a set of |
| 403 | // parameters which tells the decoder how to decompress it." |
| 404 | |
| 405 | /* this decoder assumes decompression of a single frame */ |
| 406 | decode_frame(&out, &in, parsed_dict); |
| 407 | |
| 408 | return (size_t)(out.ptr - (u8 *)dst); |
| 409 | } |
| 410 | |
| 411 | /******* FRAME DECODING ******************************************************/ |
| 412 | |
| 413 | static void decode_data_frame(ostream_t *const out, istream_t *const in, |
| 414 | const dictionary_t *const dict); |
| 415 | static void init_frame_context(frame_context_t *const context, |
| 416 | istream_t *const in, |
| 417 | const dictionary_t *const dict); |
| 418 | static void free_frame_context(frame_context_t *const context); |
| 419 | static void parse_frame_header(frame_header_t *const header, |
| 420 | istream_t *const in); |
| 421 | static void frame_context_apply_dict(frame_context_t *const ctx, |
| 422 | const dictionary_t *const dict); |
| 423 | |
| 424 | static void decompress_data(frame_context_t *const ctx, ostream_t *const out, |
| 425 | istream_t *const in); |
| 426 | |
| 427 | static void decode_frame(ostream_t *const out, istream_t *const in, |
| 428 | const dictionary_t *const dict) { |
| 429 | const u32 magic_number = (u32)IO_read_bits(in, 32); |
| 430 | if (magic_number == ZSTD_MAGIC_NUMBER) { |
| 431 | // ZSTD frame |
| 432 | decode_data_frame(out, in, dict); |
| 433 | |
| 434 | return; |
| 435 | } |
| 436 | |
| 437 | // not a real frame or a skippable frame |
| 438 | ERROR("Tried to decode non-ZSTD frame"); |
| 439 | } |
| 440 | |
| 441 | /// Decode a frame that contains compressed data. Not all frames do as there |
| 442 | /// are skippable frames. |
| 443 | /// See |
| 444 | /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#general-structure-of-zstandard-frame-format |
| 445 | static void decode_data_frame(ostream_t *const out, istream_t *const in, |
| 446 | const dictionary_t *const dict) { |
| 447 | frame_context_t ctx; |
| 448 | |
| 449 | // Initialize the context that needs to be carried from block to block |
| 450 | init_frame_context(&ctx, in, dict); |
| 451 | |
| 452 | if (ctx.header.frame_content_size != 0 && |
| 453 | ctx.header.frame_content_size > out->len) { |
| 454 | OUT_SIZE(); |
| 455 | } |
| 456 | |
| 457 | decompress_data(&ctx, out, in); |
| 458 | |
| 459 | free_frame_context(&ctx); |
| 460 | } |
| 461 | |
| 462 | /// Takes the information provided in the header and dictionary, and initializes |
| 463 | /// the context for this frame |
| 464 | static void init_frame_context(frame_context_t *const context, |
| 465 | istream_t *const in, |
| 466 | const dictionary_t *const dict) { |
| 467 | // Most fields in context are correct when initialized to 0 |
| 468 | memset(context, 0, sizeof(frame_context_t)); |
| 469 | |
| 470 | // Parse data from the frame header |
| 471 | parse_frame_header(&context->header, in); |
| 472 | |
| 473 | // Set up the offset history for the repeat offset commands |
| 474 | context->previous_offsets[0] = 1; |
| 475 | context->previous_offsets[1] = 4; |
| 476 | context->previous_offsets[2] = 8; |
| 477 | |
| 478 | // Apply details from the dict if it exists |
| 479 | frame_context_apply_dict(context, dict); |
| 480 | } |
| 481 | |
| 482 | static void free_frame_context(frame_context_t *const context) { |
| 483 | HUF_free_dtable(&context->literals_dtable); |
| 484 | |
| 485 | FSE_free_dtable(&context->ll_dtable); |
| 486 | FSE_free_dtable(&context->ml_dtable); |
| 487 | FSE_free_dtable(&context->of_dtable); |
| 488 | |
| 489 | memset(context, 0, sizeof(frame_context_t)); |
| 490 | } |
| 491 | |
| 492 | static void parse_frame_header(frame_header_t *const header, |
| 493 | istream_t *const in) { |
| 494 | // "The first header's byte is called the Frame_Header_Descriptor. It tells |
| 495 | // which other fields are present. Decoding this byte is enough to tell the |
| 496 | // size of Frame_Header. |
| 497 | // |
| 498 | // Bit number Field name |
| 499 | // 7-6 Frame_Content_Size_flag |
| 500 | // 5 Single_Segment_flag |
| 501 | // 4 Unused_bit |
| 502 | // 3 Reserved_bit |
| 503 | // 2 Content_Checksum_flag |
| 504 | // 1-0 Dictionary_ID_flag" |
| 505 | const u8 descriptor = (u8)IO_read_bits(in, 8); |
| 506 | |
| 507 | // decode frame header descriptor into flags |
| 508 | const u8 frame_content_size_flag = descriptor >> 6; |
| 509 | const u8 single_segment_flag = (descriptor >> 5) & 1; |
| 510 | const u8 reserved_bit = (descriptor >> 3) & 1; |
| 511 | const u8 content_checksum_flag = (descriptor >> 2) & 1; |
| 512 | const u8 dictionary_id_flag = descriptor & 3; |
| 513 | |
| 514 | if (reserved_bit != 0) { |
| 515 | CORRUPTION(); |
| 516 | } |
| 517 | |
| 518 | header->single_segment_flag = single_segment_flag; |
| 519 | header->content_checksum_flag = content_checksum_flag; |
| 520 | |
| 521 | // decode window size |
| 522 | if (!single_segment_flag) { |
| 523 | // "Provides guarantees on maximum back-reference distance that will be |
| 524 | // used within compressed data. This information is important for |
| 525 | // decoders to allocate enough memory. |
| 526 | // |
| 527 | // Bit numbers 7-3 2-0 |
| 528 | // Field name Exponent Mantissa" |
| 529 | u8 window_descriptor = (u8)IO_read_bits(in, 8); |
| 530 | u8 exponent = window_descriptor >> 3; |
| 531 | u8 mantissa = window_descriptor & 7; |
| 532 | |
| 533 | // Use the algorithm from the specification to compute window size |
| 534 | // https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor |
| 535 | size_t window_base = (size_t)1 << (10 + exponent); |
| 536 | size_t window_add = (window_base / 8) * mantissa; |
| 537 | header->window_size = window_base + window_add; |
| 538 | } |
| 539 | |
| 540 | // decode dictionary id if it exists |
| 541 | if (dictionary_id_flag) { |
| 542 | // "This is a variable size field, which contains the ID of the |
| 543 | // dictionary required to properly decode the frame. Note that this |
| 544 | // field is optional. When it's not present, it's up to the caller to |
| 545 | // make sure it uses the correct dictionary. Format is little-endian." |
| 546 | const int bytes_array[] = {0, 1, 2, 4}; |
| 547 | const int bytes = bytes_array[dictionary_id_flag]; |
| 548 | |
| 549 | header->dictionary_id = (u32)IO_read_bits(in, bytes * 8); |
| 550 | } else { |
| 551 | header->dictionary_id = 0; |
| 552 | } |
| 553 | |
| 554 | // decode frame content size if it exists |
| 555 | if (single_segment_flag || frame_content_size_flag) { |
| 556 | // "This is the original (uncompressed) size. This information is |
| 557 | // optional. The Field_Size is provided according to value of |
| 558 | // Frame_Content_Size_flag. The Field_Size can be equal to 0 (not |
| 559 | // present), 1, 2, 4 or 8 bytes. Format is little-endian." |
| 560 | // |
| 561 | // if frame_content_size_flag == 0 but single_segment_flag is set, we |
| 562 | // still have a 1 byte field |
| 563 | const int bytes_array[] = {1, 2, 4, 8}; |
| 564 | const int bytes = bytes_array[frame_content_size_flag]; |
| 565 | |
| 566 | header->frame_content_size = IO_read_bits(in, bytes * 8); |
| 567 | if (bytes == 2) { |
| 568 | // "When Field_Size is 2, the offset of 256 is added." |
| 569 | header->frame_content_size += 256; |
| 570 | } |
| 571 | } else { |
| 572 | header->frame_content_size = 0; |
| 573 | } |
| 574 | |
| 575 | if (single_segment_flag) { |
| 576 | // "The Window_Descriptor byte is optional. It is absent when |
| 577 | // Single_Segment_flag is set. In this case, the maximum back-reference |
| 578 | // distance is the content size itself, which can be any value from 1 to |
| 579 | // 2^64-1 bytes (16 EB)." |
| 580 | header->window_size = header->frame_content_size; |
| 581 | } |
| 582 | } |
| 583 | |
| 584 | /// Decompress the data from a frame block by block |
| 585 | static void decompress_data(frame_context_t *const ctx, ostream_t *const out, |
| 586 | istream_t *const in) { |
| 587 | // "A frame encapsulates one or multiple blocks. Each block can be |
| 588 | // compressed or not, and has a guaranteed maximum content size, which |
| 589 | // depends on frame parameters. Unlike frames, each block depends on |
| 590 | // previous blocks for proper decoding. However, each block can be |
| 591 | // decompressed without waiting for its successor, allowing streaming |
| 592 | // operations." |
| 593 | int last_block = 0; |
| 594 | do { |
| 595 | // "Last_Block |
| 596 | // |
| 597 | // The lowest bit signals if this block is the last one. Frame ends |
| 598 | // right after this block. |
| 599 | // |
| 600 | // Block_Type and Block_Size |
| 601 | // |
| 602 | // The next 2 bits represent the Block_Type, while the remaining 21 bits |
| 603 | // represent the Block_Size. Format is little-endian." |
| 604 | last_block = (int)IO_read_bits(in, 1); |
| 605 | const int block_type = (int)IO_read_bits(in, 2); |
| 606 | const size_t block_len = IO_read_bits(in, 21); |
| 607 | |
| 608 | switch (block_type) { |
| 609 | case 0: { |
| 610 | // "Raw_Block - this is an uncompressed block. Block_Size is the |
| 611 | // number of bytes to read and copy." |
| 612 | const u8 *const read_ptr = IO_get_read_ptr(in, block_len); |
| 613 | u8 *const write_ptr = IO_get_write_ptr(out, block_len); |
| 614 | |
| 615 | // Copy the raw data into the output |
| 616 | memcpy(write_ptr, read_ptr, block_len); |
| 617 | |
| 618 | ctx->current_total_output += block_len; |
| 619 | break; |
| 620 | } |
| 621 | case 1: { |
| 622 | // "RLE_Block - this is a single byte, repeated N times. In which |
| 623 | // case, Block_Size is the size to regenerate, while the |
| 624 | // "compressed" block is just 1 byte (the byte to repeat)." |
| 625 | const u8 *const read_ptr = IO_get_read_ptr(in, 1); |
| 626 | u8 *const write_ptr = IO_get_write_ptr(out, block_len); |
| 627 | |
| 628 | // Copy `block_len` copies of `read_ptr[0]` to the output |
| 629 | memset(write_ptr, read_ptr[0], block_len); |
| 630 | |
| 631 | ctx->current_total_output += block_len; |
| 632 | break; |
| 633 | } |
| 634 | case 2: { |
| 635 | // "Compressed_Block - this is a Zstandard compressed block, |
| 636 | // detailed in another section of this specification. Block_Size is |
| 637 | // the compressed size. |
| 638 | |
| 639 | // Create a sub-stream for the block |
| 640 | istream_t block_stream = IO_make_sub_istream(in, block_len); |
| 641 | decompress_block(ctx, out, &block_stream); |
| 642 | break; |
| 643 | } |
| 644 | case 3: |
| 645 | // "Reserved - this is not a block. This value cannot be used with |
| 646 | // current version of this specification." |
| 647 | CORRUPTION(); |
| 648 | break; |
| 649 | default: |
| 650 | IMPOSSIBLE(); |
| 651 | } |
| 652 | } while (!last_block); |
| 653 | |
| 654 | if (ctx->header.content_checksum_flag) { |
| 655 | // This program does not support checking the checksum, so skip over it |
| 656 | // if it's present |
| 657 | IO_advance_input(in, 4); |
| 658 | } |
| 659 | } |
| 660 | /******* END FRAME DECODING ***************************************************/ |
| 661 | |
| 662 | /******* BLOCK DECOMPRESSION **************************************************/ |
| 663 | static void decompress_block(frame_context_t *const ctx, ostream_t *const out, |
| 664 | istream_t *const in) { |
| 665 | // "A compressed block consists of 2 sections : |
| 666 | // |
| 667 | // Literals_Section |
| 668 | // Sequences_Section" |
| 669 | |
| 670 | |
| 671 | // Part 1: decode the literals block |
| 672 | u8 *literals = NULL; |
| 673 | const size_t literals_size = decode_literals(ctx, in, &literals); |
| 674 | |
| 675 | // Part 2: decode the sequences block |
| 676 | sequence_command_t *sequences = NULL; |
| 677 | const size_t num_sequences = |
| 678 | decode_sequences(ctx, in, &sequences); |
| 679 | |
| 680 | // Part 3: combine literals and sequence commands to generate output |
| 681 | execute_sequences(ctx, out, literals, literals_size, sequences, |
| 682 | num_sequences); |
| 683 | free(literals); |
| 684 | free(sequences); |
| 685 | } |
| 686 | /******* END BLOCK DECOMPRESSION **********************************************/ |
| 687 | |
| 688 | /******* LITERALS DECODING ****************************************************/ |
| 689 | static size_t decode_literals_simple(istream_t *const in, u8 **const literals, |
| 690 | const int block_type, |
| 691 | const int size_format); |
| 692 | static size_t decode_literals_compressed(frame_context_t *const ctx, |
| 693 | istream_t *const in, |
| 694 | u8 **const literals, |
| 695 | const int block_type, |
| 696 | const int size_format); |
| 697 | static void decode_huf_table(HUF_dtable *const dtable, istream_t *const in); |
| 698 | static void fse_decode_hufweights(ostream_t *weights, istream_t *const in, |
| 699 | int *const num_symbs); |
| 700 | |
| 701 | static size_t decode_literals(frame_context_t *const ctx, istream_t *const in, |
| 702 | u8 **const literals) { |
| 703 | // "Literals can be stored uncompressed or compressed using Huffman prefix |
| 704 | // codes. When compressed, an optional tree description can be present, |
| 705 | // followed by 1 or 4 streams." |
| 706 | // |
| 707 | // "Literals_Section_Header |
| 708 | // |
| 709 | // Header is in charge of describing how literals are packed. It's a |
| 710 | // byte-aligned variable-size bitfield, ranging from 1 to 5 bytes, using |
| 711 | // little-endian convention." |
| 712 | // |
| 713 | // "Literals_Block_Type |
| 714 | // |
| 715 | // This field uses 2 lowest bits of first byte, describing 4 different block |
| 716 | // types" |
| 717 | // |
| 718 | // size_format takes between 1 and 2 bits |
| 719 | int block_type = (int)IO_read_bits(in, 2); |
| 720 | int size_format = (int)IO_read_bits(in, 2); |
| 721 | |
| 722 | if (block_type <= 1) { |
| 723 | // Raw or RLE literals block |
| 724 | return decode_literals_simple(in, literals, block_type, |
| 725 | size_format); |
| 726 | } else { |
| 727 | // Huffman compressed literals |
| 728 | return decode_literals_compressed(ctx, in, literals, block_type, |
| 729 | size_format); |
| 730 | } |
| 731 | } |
| 732 | |
| 733 | /// Decodes literals blocks in raw or RLE form |
| 734 | static size_t decode_literals_simple(istream_t *const in, u8 **const literals, |
| 735 | const int block_type, |
| 736 | const int size_format) { |
| 737 | size_t size; |
| 738 | switch (size_format) { |
| 739 | // These cases are in the form ?0 |
| 740 | // In this case, the ? bit is actually part of the size field |
| 741 | case 0: |
| 742 | case 2: |
| 743 | // "Size_Format uses 1 bit. Regenerated_Size uses 5 bits (0-31)." |
| 744 | IO_rewind_bits(in, 1); |
| 745 | size = IO_read_bits(in, 5); |
| 746 | break; |
| 747 | case 1: |
| 748 | // "Size_Format uses 2 bits. Regenerated_Size uses 12 bits (0-4095)." |
| 749 | size = IO_read_bits(in, 12); |
| 750 | break; |
| 751 | case 3: |
| 752 | // "Size_Format uses 2 bits. Regenerated_Size uses 20 bits (0-1048575)." |
| 753 | size = IO_read_bits(in, 20); |
| 754 | break; |
| 755 | default: |
| 756 | // Size format is in range 0-3 |
| 757 | IMPOSSIBLE(); |
| 758 | } |
| 759 | |
| 760 | if (size > MAX_LITERALS_SIZE) { |
| 761 | CORRUPTION(); |
| 762 | } |
| 763 | |
| 764 | *literals = malloc(size); |
| 765 | if (!*literals) { |
| 766 | BAD_ALLOC(); |
| 767 | } |
| 768 | |
| 769 | switch (block_type) { |
| 770 | case 0: { |
| 771 | // "Raw_Literals_Block - Literals are stored uncompressed." |
| 772 | const u8 *const read_ptr = IO_get_read_ptr(in, size); |
| 773 | memcpy(*literals, read_ptr, size); |
| 774 | break; |
| 775 | } |
| 776 | case 1: { |
| 777 | // "RLE_Literals_Block - Literals consist of a single byte value repeated N times." |
| 778 | const u8 *const read_ptr = IO_get_read_ptr(in, 1); |
| 779 | memset(*literals, read_ptr[0], size); |
| 780 | break; |
| 781 | } |
| 782 | default: |
| 783 | IMPOSSIBLE(); |
| 784 | } |
| 785 | |
| 786 | return size; |
| 787 | } |
| 788 | |
| 789 | /// Decodes Huffman compressed literals |
| 790 | static size_t decode_literals_compressed(frame_context_t *const ctx, |
| 791 | istream_t *const in, |
| 792 | u8 **const literals, |
| 793 | const int block_type, |
| 794 | const int size_format) { |
| 795 | size_t regenerated_size, compressed_size; |
| 796 | // Only size_format=0 has 1 stream, so default to 4 |
| 797 | int num_streams = 4; |
| 798 | switch (size_format) { |
| 799 | case 0: |
| 800 | // "A single stream. Both Compressed_Size and Regenerated_Size use 10 |
| 801 | // bits (0-1023)." |
| 802 | num_streams = 1; |
| 803 | // Fall through as it has the same size format |
| 804 | /* fallthrough */ |
| 805 | case 1: |
| 806 | // "4 streams. Both Compressed_Size and Regenerated_Size use 10 bits |
| 807 | // (0-1023)." |
| 808 | regenerated_size = IO_read_bits(in, 10); |
| 809 | compressed_size = IO_read_bits(in, 10); |
| 810 | break; |
| 811 | case 2: |
| 812 | // "4 streams. Both Compressed_Size and Regenerated_Size use 14 bits |
| 813 | // (0-16383)." |
| 814 | regenerated_size = IO_read_bits(in, 14); |
| 815 | compressed_size = IO_read_bits(in, 14); |
| 816 | break; |
| 817 | case 3: |
| 818 | // "4 streams. Both Compressed_Size and Regenerated_Size use 18 bits |
| 819 | // (0-262143)." |
| 820 | regenerated_size = IO_read_bits(in, 18); |
| 821 | compressed_size = IO_read_bits(in, 18); |
| 822 | break; |
| 823 | default: |
| 824 | // Impossible |
| 825 | IMPOSSIBLE(); |
| 826 | } |
| 827 | if (regenerated_size > MAX_LITERALS_SIZE) { |
| 828 | CORRUPTION(); |
| 829 | } |
| 830 | |
| 831 | *literals = malloc(regenerated_size); |
| 832 | if (!*literals) { |
| 833 | BAD_ALLOC(); |
| 834 | } |
| 835 | |
| 836 | ostream_t lit_stream = IO_make_ostream(*literals, regenerated_size); |
| 837 | istream_t huf_stream = IO_make_sub_istream(in, compressed_size); |
| 838 | |
| 839 | if (block_type == 2) { |
| 840 | // Decode the provided Huffman table |
| 841 | // "This section is only present when Literals_Block_Type type is |
| 842 | // Compressed_Literals_Block (2)." |
| 843 | |
| 844 | HUF_free_dtable(&ctx->literals_dtable); |
| 845 | decode_huf_table(&ctx->literals_dtable, &huf_stream); |
| 846 | } else { |
| 847 | // If the previous Huffman table is being repeated, ensure it exists |
| 848 | if (!ctx->literals_dtable.symbols) { |
| 849 | CORRUPTION(); |
| 850 | } |
| 851 | } |
| 852 | |
| 853 | size_t symbols_decoded; |
| 854 | if (num_streams == 1) { |
| 855 | symbols_decoded = HUF_decompress_1stream(&ctx->literals_dtable, &lit_stream, &huf_stream); |
| 856 | } else { |
| 857 | symbols_decoded = HUF_decompress_4stream(&ctx->literals_dtable, &lit_stream, &huf_stream); |
| 858 | } |
| 859 | |
| 860 | if (symbols_decoded != regenerated_size) { |
| 861 | CORRUPTION(); |
| 862 | } |
| 863 | |
| 864 | return regenerated_size; |
| 865 | } |
| 866 | |
| 867 | // Decode the Huffman table description |
| 868 | static void decode_huf_table(HUF_dtable *const dtable, istream_t *const in) { |
| 869 | // "All literal values from zero (included) to last present one (excluded) |
| 870 | // are represented by Weight with values from 0 to Max_Number_of_Bits." |
| 871 | |
| 872 | // "This is a single byte value (0-255), which describes how to decode the list of weights." |
| 873 | const u8 header = IO_read_bits(in, 8); |
| 874 | |
| 875 | u8 weights[HUF_MAX_SYMBS]; |
| 876 | memset(weights, 0, sizeof(weights)); |
| 877 | |
| 878 | int num_symbs; |
| 879 | |
| 880 | if (header >= 128) { |
| 881 | // "This is a direct representation, where each Weight is written |
| 882 | // directly as a 4 bits field (0-15). The full representation occupies |
| 883 | // ((Number_of_Symbols+1)/2) bytes, meaning it uses a last full byte |
| 884 | // even if Number_of_Symbols is odd. Number_of_Symbols = headerByte - |
| 885 | // 127" |
| 886 | num_symbs = header - 127; |
| 887 | const size_t bytes = (num_symbs + 1) / 2; |
| 888 | |
| 889 | const u8 *const weight_src = IO_get_read_ptr(in, bytes); |
| 890 | |
| 891 | for (int i = 0; i < num_symbs; i++) { |
| 892 | // "They are encoded forward, 2 |
| 893 | // weights to a byte with the first weight taking the top four bits |
| 894 | // and the second taking the bottom four (e.g. the following |
| 895 | // operations could be used to read the weights: Weight[0] = |
| 896 | // (Byte[0] >> 4), Weight[1] = (Byte[0] & 0xf), etc.)." |
| 897 | if (i % 2 == 0) { |
| 898 | weights[i] = weight_src[i / 2] >> 4; |
| 899 | } else { |
| 900 | weights[i] = weight_src[i / 2] & 0xf; |
| 901 | } |
| 902 | } |
| 903 | } else { |
| 904 | // The weights are FSE encoded, decode them before we can construct the |
| 905 | // table |
| 906 | istream_t fse_stream = IO_make_sub_istream(in, header); |
| 907 | ostream_t weight_stream = IO_make_ostream(weights, HUF_MAX_SYMBS); |
| 908 | fse_decode_hufweights(&weight_stream, &fse_stream, &num_symbs); |
| 909 | } |
| 910 | |
| 911 | // Construct the table using the decoded weights |
| 912 | HUF_init_dtable_usingweights(dtable, weights, num_symbs); |
| 913 | } |
| 914 | |
| 915 | static void fse_decode_hufweights(ostream_t *weights, istream_t *const in, |
| 916 | int *const num_symbs) { |
| 917 | const int MAX_ACCURACY_LOG = 7; |
| 918 | |
| 919 | FSE_dtable dtable; |
| 920 | |
| 921 | // "An FSE bitstream starts by a header, describing probabilities |
| 922 | // distribution. It will create a Decoding Table. For a list of Huffman |
| 923 | // weights, maximum accuracy is 7 bits." |
| 924 | FSE_decode_header(&dtable, in, MAX_ACCURACY_LOG); |
| 925 | |
| 926 | // Decode the weights |
| 927 | *num_symbs = FSE_decompress_interleaved2(&dtable, weights, in); |
| 928 | |
| 929 | FSE_free_dtable(&dtable); |
| 930 | } |
| 931 | /******* END LITERALS DECODING ************************************************/ |
| 932 | |
| 933 | /******* SEQUENCE DECODING ****************************************************/ |
| 934 | /// The combination of FSE states needed to decode sequences |
| 935 | typedef struct { |
| 936 | FSE_dtable ll_table; |
| 937 | FSE_dtable of_table; |
| 938 | FSE_dtable ml_table; |
| 939 | |
| 940 | u16 ll_state; |
| 941 | u16 of_state; |
| 942 | u16 ml_state; |
| 943 | } sequence_states_t; |
| 944 | |
| 945 | /// Different modes to signal to decode_seq_tables what to do |
| 946 | typedef enum { |
| 947 | seq_literal_length = 0, |
| 948 | seq_offset = 1, |
| 949 | seq_match_length = 2, |
| 950 | } seq_part_t; |
| 951 | |
| 952 | typedef enum { |
| 953 | seq_predefined = 0, |
| 954 | seq_rle = 1, |
| 955 | seq_fse = 2, |
| 956 | seq_repeat = 3, |
| 957 | } seq_mode_t; |
| 958 | |
| 959 | /// The predefined FSE distribution tables for `seq_predefined` mode |
| 960 | static const i16 SEQ_LITERAL_LENGTH_DEFAULT_DIST[36] = { |
| 961 | 4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 2, |
| 962 | 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1, -1, -1, -1, -1}; |
| 963 | static const i16 SEQ_OFFSET_DEFAULT_DIST[29] = { |
| 964 | 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, |
| 965 | 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1}; |
| 966 | static const i16 SEQ_MATCH_LENGTH_DEFAULT_DIST[53] = { |
| 967 | 1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
| 968 | 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
| 969 | 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1}; |
| 970 | |
| 971 | /// The sequence decoding baseline and number of additional bits to read/add |
| 972 | /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#the-codes-for-literals-lengths-match-lengths-and-offsets |
| 973 | static const u32 SEQ_LITERAL_LENGTH_BASELINES[36] = { |
| 974 | 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, |
| 975 | 12, 13, 14, 15, 16, 18, 20, 22, 24, 28, 32, 40, |
| 976 | 48, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536}; |
| 977 | static const u8 SEQ_LITERAL_LENGTH_EXTRA_BITS[36] = { |
| 978 | 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, |
| 979 | 1, 1, 2, 2, 3, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; |
| 980 | |
| 981 | static const u32 SEQ_MATCH_LENGTH_BASELINES[53] = { |
| 982 | 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, |
| 983 | 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, |
| 984 | 31, 32, 33, 34, 35, 37, 39, 41, 43, 47, 51, 59, 67, 83, |
| 985 | 99, 131, 259, 515, 1027, 2051, 4099, 8195, 16387, 32771, 65539}; |
| 986 | static const u8 SEQ_MATCH_LENGTH_EXTRA_BITS[53] = { |
| 987 | 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
| 988 | 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, |
| 989 | 2, 2, 3, 3, 4, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; |
| 990 | |
| 991 | /// Offset decoding is simpler so we just need a maximum code value |
| 992 | static const u8 SEQ_MAX_CODES[3] = {35, (u8)-1, 52}; |
| 993 | |
| 994 | static void decompress_sequences(frame_context_t *const ctx, |
| 995 | istream_t *const in, |
| 996 | sequence_command_t *const sequences, |
| 997 | const size_t num_sequences); |
| 998 | static sequence_command_t decode_sequence(sequence_states_t *const state, |
| 999 | const u8 *const src, |
| 1000 | i64 *const offset); |
| 1001 | static void decode_seq_table(FSE_dtable *const table, istream_t *const in, |
| 1002 | const seq_part_t type, const seq_mode_t mode); |
| 1003 | |
| 1004 | static size_t decode_sequences(frame_context_t *const ctx, istream_t *in, |
| 1005 | sequence_command_t **const sequences) { |
| 1006 | // "A compressed block is a succession of sequences . A sequence is a |
| 1007 | // literal copy command, followed by a match copy command. A literal copy |
| 1008 | // command specifies a length. It is the number of bytes to be copied (or |
| 1009 | // extracted) from the literal section. A match copy command specifies an |
| 1010 | // offset and a length. The offset gives the position to copy from, which |
| 1011 | // can be within a previous block." |
| 1012 | |
| 1013 | size_t num_sequences; |
| 1014 | |
| 1015 | // "Number_of_Sequences |
| 1016 | // |
| 1017 | // This is a variable size field using between 1 and 3 bytes. Let's call its |
| 1018 | // first byte byte0." |
| 1019 | u8 header = IO_read_bits(in, 8); |
| 1020 | if (header == 0) { |
| 1021 | // "There are no sequences. The sequence section stops there. |
| 1022 | // Regenerated content is defined entirely by literals section." |
| 1023 | *sequences = NULL; |
| 1024 | return 0; |
| 1025 | } else if (header < 128) { |
| 1026 | // "Number_of_Sequences = byte0 . Uses 1 byte." |
| 1027 | num_sequences = header; |
| 1028 | } else if (header < 255) { |
| 1029 | // "Number_of_Sequences = ((byte0-128) << 8) + byte1 . Uses 2 bytes." |
| 1030 | num_sequences = ((header - 128) << 8) + IO_read_bits(in, 8); |
| 1031 | } else { |
| 1032 | // "Number_of_Sequences = byte1 + (byte2<<8) + 0x7F00 . Uses 3 bytes." |
| 1033 | num_sequences = IO_read_bits(in, 16) + 0x7F00; |
| 1034 | } |
| 1035 | |
| 1036 | *sequences = malloc(num_sequences * sizeof(sequence_command_t)); |
| 1037 | if (!*sequences) { |
| 1038 | BAD_ALLOC(); |
| 1039 | } |
| 1040 | |
| 1041 | decompress_sequences(ctx, in, *sequences, num_sequences); |
| 1042 | return num_sequences; |
| 1043 | } |
| 1044 | |
| 1045 | /// Decompress the FSE encoded sequence commands |
| 1046 | static void decompress_sequences(frame_context_t *const ctx, istream_t *in, |
| 1047 | sequence_command_t *const sequences, |
| 1048 | const size_t num_sequences) { |
| 1049 | // "The Sequences_Section regroup all symbols required to decode commands. |
| 1050 | // There are 3 symbol types : literals lengths, offsets and match lengths. |
| 1051 | // They are encoded together, interleaved, in a single bitstream." |
| 1052 | |
| 1053 | // "Symbol compression modes |
| 1054 | // |
| 1055 | // This is a single byte, defining the compression mode of each symbol |
| 1056 | // type." |
| 1057 | // |
| 1058 | // Bit number : Field name |
| 1059 | // 7-6 : Literals_Lengths_Mode |
| 1060 | // 5-4 : Offsets_Mode |
| 1061 | // 3-2 : Match_Lengths_Mode |
| 1062 | // 1-0 : Reserved |
| 1063 | u8 compression_modes = IO_read_bits(in, 8); |
| 1064 | |
| 1065 | if ((compression_modes & 3) != 0) { |
| 1066 | // Reserved bits set |
| 1067 | CORRUPTION(); |
| 1068 | } |
| 1069 | |
| 1070 | // "Following the header, up to 3 distribution tables can be described. When |
| 1071 | // present, they are in this order : |
| 1072 | // |
| 1073 | // Literals lengths |
| 1074 | // Offsets |
| 1075 | // Match Lengths" |
| 1076 | // Update the tables we have stored in the context |
| 1077 | decode_seq_table(&ctx->ll_dtable, in, seq_literal_length, |
| 1078 | (compression_modes >> 6) & 3); |
| 1079 | |
| 1080 | decode_seq_table(&ctx->of_dtable, in, seq_offset, |
| 1081 | (compression_modes >> 4) & 3); |
| 1082 | |
| 1083 | decode_seq_table(&ctx->ml_dtable, in, seq_match_length, |
| 1084 | (compression_modes >> 2) & 3); |
| 1085 | |
| 1086 | |
| 1087 | sequence_states_t states; |
| 1088 | |
| 1089 | // Initialize the decoding tables |
| 1090 | { |
| 1091 | states.ll_table = ctx->ll_dtable; |
| 1092 | states.of_table = ctx->of_dtable; |
| 1093 | states.ml_table = ctx->ml_dtable; |
| 1094 | } |
| 1095 | |
| 1096 | const size_t len = IO_istream_len(in); |
| 1097 | const u8 *const src = IO_get_read_ptr(in, len); |
| 1098 | |
| 1099 | // "After writing the last bit containing information, the compressor writes |
| 1100 | // a single 1-bit and then fills the byte with 0-7 0 bits of padding." |
| 1101 | const int padding = 8 - highest_set_bit(src[len - 1]); |
| 1102 | // The offset starts at the end because FSE streams are read backwards |
| 1103 | i64 bit_offset = (i64)(len * 8 - (size_t)padding); |
| 1104 | |
| 1105 | // "The bitstream starts with initial state values, each using the required |
| 1106 | // number of bits in their respective accuracy, decoded previously from |
| 1107 | // their normalized distribution. |
| 1108 | // |
| 1109 | // It starts by Literals_Length_State, followed by Offset_State, and finally |
| 1110 | // Match_Length_State." |
| 1111 | FSE_init_state(&states.ll_table, &states.ll_state, src, &bit_offset); |
| 1112 | FSE_init_state(&states.of_table, &states.of_state, src, &bit_offset); |
| 1113 | FSE_init_state(&states.ml_table, &states.ml_state, src, &bit_offset); |
| 1114 | |
| 1115 | for (size_t i = 0; i < num_sequences; i++) { |
| 1116 | // Decode sequences one by one |
| 1117 | sequences[i] = decode_sequence(&states, src, &bit_offset); |
| 1118 | } |
| 1119 | |
| 1120 | if (bit_offset != 0) { |
| 1121 | CORRUPTION(); |
| 1122 | } |
| 1123 | } |
| 1124 | |
| 1125 | // Decode a single sequence and update the state |
| 1126 | static sequence_command_t decode_sequence(sequence_states_t *const states, |
| 1127 | const u8 *const src, |
| 1128 | i64 *const offset) { |
| 1129 | // "Each symbol is a code in its own context, which specifies Baseline and |
| 1130 | // Number_of_Bits to add. Codes are FSE compressed, and interleaved with raw |
| 1131 | // additional bits in the same bitstream." |
| 1132 | |
| 1133 | // Decode symbols, but don't update states |
| 1134 | const u8 of_code = FSE_peek_symbol(&states->of_table, states->of_state); |
| 1135 | const u8 ll_code = FSE_peek_symbol(&states->ll_table, states->ll_state); |
| 1136 | const u8 ml_code = FSE_peek_symbol(&states->ml_table, states->ml_state); |
| 1137 | |
| 1138 | // Offset doesn't need a max value as it's not decoded using a table |
| 1139 | if (ll_code > SEQ_MAX_CODES[seq_literal_length] || |
| 1140 | ml_code > SEQ_MAX_CODES[seq_match_length]) { |
| 1141 | CORRUPTION(); |
| 1142 | } |
| 1143 | |
| 1144 | // Read the interleaved bits |
| 1145 | sequence_command_t seq; |
| 1146 | // "Decoding starts by reading the Number_of_Bits required to decode Offset. |
| 1147 | // It then does the same for Match_Length, and then for Literals_Length." |
| 1148 | seq.offset = ((u32)1 << of_code) + STREAM_read_bits(src, of_code, offset); |
| 1149 | |
| 1150 | seq.match_length = |
| 1151 | SEQ_MATCH_LENGTH_BASELINES[ml_code] + |
| 1152 | STREAM_read_bits(src, SEQ_MATCH_LENGTH_EXTRA_BITS[ml_code], offset); |
| 1153 | |
| 1154 | seq.literal_length = |
| 1155 | SEQ_LITERAL_LENGTH_BASELINES[ll_code] + |
| 1156 | STREAM_read_bits(src, SEQ_LITERAL_LENGTH_EXTRA_BITS[ll_code], offset); |
| 1157 | |
| 1158 | // "If it is not the last sequence in the block, the next operation is to |
| 1159 | // update states. Using the rules pre-calculated in the decoding tables, |
| 1160 | // Literals_Length_State is updated, followed by Match_Length_State, and |
| 1161 | // then Offset_State." |
| 1162 | // If the stream is complete don't read bits to update state |
| 1163 | if (*offset != 0) { |
| 1164 | FSE_update_state(&states->ll_table, &states->ll_state, src, offset); |
| 1165 | FSE_update_state(&states->ml_table, &states->ml_state, src, offset); |
| 1166 | FSE_update_state(&states->of_table, &states->of_state, src, offset); |
| 1167 | } |
| 1168 | |
| 1169 | return seq; |
| 1170 | } |
| 1171 | |
| 1172 | /// Given a sequence part and table mode, decode the FSE distribution |
| 1173 | /// Errors if the mode is `seq_repeat` without a pre-existing table in `table` |
| 1174 | static void decode_seq_table(FSE_dtable *const table, istream_t *const in, |
| 1175 | const seq_part_t type, const seq_mode_t mode) { |
| 1176 | // Constant arrays indexed by seq_part_t |
| 1177 | const i16 *const default_distributions[] = {SEQ_LITERAL_LENGTH_DEFAULT_DIST, |
| 1178 | SEQ_OFFSET_DEFAULT_DIST, |
| 1179 | SEQ_MATCH_LENGTH_DEFAULT_DIST}; |
| 1180 | const size_t default_distribution_lengths[] = {36, 29, 53}; |
| 1181 | const size_t default_distribution_accuracies[] = {6, 5, 6}; |
| 1182 | |
| 1183 | const size_t max_accuracies[] = {9, 8, 9}; |
| 1184 | |
| 1185 | if (mode != seq_repeat) { |
| 1186 | // Free old one before overwriting |
| 1187 | FSE_free_dtable(table); |
| 1188 | } |
| 1189 | |
| 1190 | switch (mode) { |
| 1191 | case seq_predefined: { |
| 1192 | // "Predefined_Mode : uses a predefined distribution table." |
| 1193 | const i16 *distribution = default_distributions[type]; |
| 1194 | const size_t symbs = default_distribution_lengths[type]; |
| 1195 | const size_t accuracy_log = default_distribution_accuracies[type]; |
| 1196 | |
| 1197 | FSE_init_dtable(table, distribution, symbs, accuracy_log); |
| 1198 | break; |
| 1199 | } |
| 1200 | case seq_rle: { |
| 1201 | // "RLE_Mode : it's a single code, repeated Number_of_Sequences times." |
| 1202 | const u8 symb = IO_get_read_ptr(in, 1)[0]; |
| 1203 | FSE_init_dtable_rle(table, symb); |
| 1204 | break; |
| 1205 | } |
| 1206 | case seq_fse: { |
| 1207 | // "FSE_Compressed_Mode : standard FSE compression. A distribution table |
| 1208 | // will be present " |
| 1209 | FSE_decode_header(table, in, max_accuracies[type]); |
| 1210 | break; |
| 1211 | } |
| 1212 | case seq_repeat: |
| 1213 | // "Repeat_Mode : re-use distribution table from previous compressed |
| 1214 | // block." |
| 1215 | // Nothing to do here, table will be unchanged |
| 1216 | if (!table->symbols) { |
| 1217 | // This mode is invalid if we don't already have a table |
| 1218 | CORRUPTION(); |
| 1219 | } |
| 1220 | break; |
| 1221 | default: |
| 1222 | // Impossible, as mode is from 0-3 |
| 1223 | IMPOSSIBLE(); |
| 1224 | break; |
| 1225 | } |
| 1226 | |
| 1227 | } |
| 1228 | /******* END SEQUENCE DECODING ************************************************/ |
| 1229 | |
| 1230 | /******* SEQUENCE EXECUTION ***************************************************/ |
| 1231 | static void execute_sequences(frame_context_t *const ctx, ostream_t *const out, |
| 1232 | const u8 *const literals, |
| 1233 | const size_t literals_len, |
| 1234 | const sequence_command_t *const sequences, |
| 1235 | const size_t num_sequences) { |
| 1236 | istream_t litstream = IO_make_istream(literals, literals_len); |
| 1237 | |
| 1238 | u64 *const offset_hist = ctx->previous_offsets; |
| 1239 | size_t total_output = ctx->current_total_output; |
| 1240 | |
| 1241 | for (size_t i = 0; i < num_sequences; i++) { |
| 1242 | const sequence_command_t seq = sequences[i]; |
| 1243 | { |
| 1244 | const u32 literals_size = copy_literals(seq.literal_length, &litstream, out); |
| 1245 | total_output += literals_size; |
| 1246 | } |
| 1247 | |
| 1248 | size_t const offset = compute_offset(seq, offset_hist); |
| 1249 | |
| 1250 | size_t const match_length = seq.match_length; |
| 1251 | |
| 1252 | execute_match_copy(ctx, offset, match_length, total_output, out); |
| 1253 | |
| 1254 | total_output += match_length; |
| 1255 | } |
| 1256 | |
| 1257 | // Copy any leftover literals |
| 1258 | { |
| 1259 | size_t len = IO_istream_len(&litstream); |
| 1260 | copy_literals(len, &litstream, out); |
| 1261 | total_output += len; |
| 1262 | } |
| 1263 | |
| 1264 | ctx->current_total_output = total_output; |
| 1265 | } |
| 1266 | |
| 1267 | static u32 copy_literals(const size_t literal_length, istream_t *litstream, |
| 1268 | ostream_t *const out) { |
| 1269 | // If the sequence asks for more literals than are left, the |
| 1270 | // sequence must be corrupted |
| 1271 | if (literal_length > IO_istream_len(litstream)) { |
| 1272 | CORRUPTION(); |
| 1273 | } |
| 1274 | |
| 1275 | u8 *const write_ptr = IO_get_write_ptr(out, literal_length); |
| 1276 | const u8 *const read_ptr = |
| 1277 | IO_get_read_ptr(litstream, literal_length); |
| 1278 | // Copy literals to output |
| 1279 | memcpy(write_ptr, read_ptr, literal_length); |
| 1280 | |
| 1281 | return literal_length; |
| 1282 | } |
| 1283 | |
| 1284 | static size_t compute_offset(sequence_command_t seq, u64 *const offset_hist) { |
| 1285 | size_t offset; |
| 1286 | // Offsets are special, we need to handle the repeat offsets |
| 1287 | if (seq.offset <= 3) { |
| 1288 | // "The first 3 values define a repeated offset and we will call |
| 1289 | // them Repeated_Offset1, Repeated_Offset2, and Repeated_Offset3. |
| 1290 | // They are sorted in recency order, with Repeated_Offset1 meaning |
| 1291 | // 'most recent one'". |
| 1292 | |
| 1293 | // Use 0 indexing for the array |
| 1294 | u32 idx = seq.offset - 1; |
| 1295 | if (seq.literal_length == 0) { |
| 1296 | // "There is an exception though, when current sequence's |
| 1297 | // literals length is 0. In this case, repeated offsets are |
| 1298 | // shifted by one, so Repeated_Offset1 becomes Repeated_Offset2, |
| 1299 | // Repeated_Offset2 becomes Repeated_Offset3, and |
| 1300 | // Repeated_Offset3 becomes Repeated_Offset1 - 1_byte." |
| 1301 | idx++; |
| 1302 | } |
| 1303 | |
| 1304 | if (idx == 0) { |
| 1305 | offset = offset_hist[0]; |
| 1306 | } else { |
| 1307 | // If idx == 3 then literal length was 0 and the offset was 3, |
| 1308 | // as per the exception listed above |
| 1309 | offset = idx < 3 ? offset_hist[idx] : offset_hist[0] - 1; |
| 1310 | |
| 1311 | // If idx == 1 we don't need to modify offset_hist[2], since |
| 1312 | // we're using the second-most recent code |
| 1313 | if (idx > 1) { |
| 1314 | offset_hist[2] = offset_hist[1]; |
| 1315 | } |
| 1316 | offset_hist[1] = offset_hist[0]; |
| 1317 | offset_hist[0] = offset; |
| 1318 | } |
| 1319 | } else { |
| 1320 | // When it's not a repeat offset: |
| 1321 | // "if (Offset_Value > 3) offset = Offset_Value - 3;" |
| 1322 | offset = seq.offset - 3; |
| 1323 | |
| 1324 | // Shift back history |
| 1325 | offset_hist[2] = offset_hist[1]; |
| 1326 | offset_hist[1] = offset_hist[0]; |
| 1327 | offset_hist[0] = offset; |
| 1328 | } |
| 1329 | return offset; |
| 1330 | } |
| 1331 | |
| 1332 | static void execute_match_copy(frame_context_t *const ctx, size_t offset, |
| 1333 | size_t match_length, size_t total_output, |
| 1334 | ostream_t *const out) { |
| 1335 | u8 *write_ptr = IO_get_write_ptr(out, match_length); |
| 1336 | if (total_output <= ctx->header.window_size) { |
| 1337 | // In this case offset might go back into the dictionary |
| 1338 | if (offset > total_output + ctx->dict_content_len) { |
| 1339 | // The offset goes beyond even the dictionary |
| 1340 | CORRUPTION(); |
| 1341 | } |
| 1342 | |
| 1343 | if (offset > total_output) { |
| 1344 | // "The rest of the dictionary is its content. The content act |
| 1345 | // as a "past" in front of data to compress or decompress, so it |
| 1346 | // can be referenced in sequence commands." |
| 1347 | const size_t dict_copy = |
| 1348 | MIN(offset - total_output, match_length); |
| 1349 | const size_t dict_offset = |
| 1350 | ctx->dict_content_len - (offset - total_output); |
| 1351 | |
| 1352 | memcpy(write_ptr, ctx->dict_content + dict_offset, dict_copy); |
| 1353 | write_ptr += dict_copy; |
| 1354 | match_length -= dict_copy; |
| 1355 | } |
| 1356 | } else if (offset > ctx->header.window_size) { |
| 1357 | CORRUPTION(); |
| 1358 | } |
| 1359 | |
| 1360 | // We must copy byte by byte because the match length might be larger |
| 1361 | // than the offset |
| 1362 | // ex: if the output so far was "abc", a command with offset=3 and |
| 1363 | // match_length=6 would produce "abcabcabc" as the new output |
| 1364 | for (size_t j = 0; j < match_length; j++) { |
| 1365 | *write_ptr = *(write_ptr - offset); |
| 1366 | write_ptr++; |
| 1367 | } |
| 1368 | } |
| 1369 | /******* END SEQUENCE EXECUTION ***********************************************/ |
| 1370 | |
| 1371 | /******* OUTPUT SIZE COUNTING *************************************************/ |
| 1372 | /// Get the decompressed size of an input stream so memory can be allocated in |
| 1373 | /// advance. |
| 1374 | /// This implementation assumes `src` points to a single ZSTD-compressed frame |
| 1375 | size_t ZSTD_get_decompressed_size(const void *src, const size_t src_len) { |
| 1376 | istream_t in = IO_make_istream(src, src_len); |
| 1377 | |
| 1378 | // get decompressed size from ZSTD frame header |
| 1379 | { |
| 1380 | const u32 magic_number = (u32)IO_read_bits(&in, 32); |
| 1381 | |
| 1382 | if (magic_number == ZSTD_MAGIC_NUMBER) { |
| 1383 | // ZSTD frame |
| 1384 | frame_header_t header; |
| 1385 | parse_frame_header(&header, &in); |
| 1386 | |
| 1387 | if (header.frame_content_size == 0 && !header.single_segment_flag) { |
| 1388 | // Content size not provided, we can't tell |
| 1389 | return (size_t)-1; |
| 1390 | } |
| 1391 | |
| 1392 | return header.frame_content_size; |
| 1393 | } else { |
| 1394 | // not a real frame or skippable frame |
| 1395 | ERROR("ZSTD frame magic number did not match"); |
| 1396 | } |
| 1397 | } |
| 1398 | } |
| 1399 | /******* END OUTPUT SIZE COUNTING *********************************************/ |
| 1400 | |
| 1401 | /******* DICTIONARY PARSING ***************************************************/ |
| 1402 | dictionary_t* create_dictionary() { |
| 1403 | dictionary_t* const dict = calloc(1, sizeof(dictionary_t)); |
| 1404 | if (!dict) { |
| 1405 | BAD_ALLOC(); |
| 1406 | } |
| 1407 | return dict; |
| 1408 | } |
| 1409 | |
| 1410 | /// Free an allocated dictionary |
| 1411 | void free_dictionary(dictionary_t *const dict) { |
| 1412 | HUF_free_dtable(&dict->literals_dtable); |
| 1413 | FSE_free_dtable(&dict->ll_dtable); |
| 1414 | FSE_free_dtable(&dict->of_dtable); |
| 1415 | FSE_free_dtable(&dict->ml_dtable); |
| 1416 | |
| 1417 | free(dict->content); |
| 1418 | |
| 1419 | memset(dict, 0, sizeof(dictionary_t)); |
| 1420 | |
| 1421 | free(dict); |
| 1422 | } |
| 1423 | |
| 1424 | |
| 1425 | #if !defined(ZDEC_NO_DICTIONARY) |
| 1426 | #define DICT_SIZE_ERROR() ERROR("Dictionary size cannot be less than 8 bytes") |
| 1427 | #define NULL_SRC() ERROR("Tried to create dictionary with pointer to null src"); |
| 1428 | |
| 1429 | static void init_dictionary_content(dictionary_t *const dict, |
| 1430 | istream_t *const in); |
| 1431 | |
| 1432 | void parse_dictionary(dictionary_t *const dict, const void *src, |
| 1433 | size_t src_len) { |
| 1434 | const u8 *byte_src = (const u8 *)src; |
| 1435 | memset(dict, 0, sizeof(dictionary_t)); |
| 1436 | if (src == NULL) { /* cannot initialize dictionary with null src */ |
| 1437 | NULL_SRC(); |
| 1438 | } |
| 1439 | if (src_len < 8) { |
| 1440 | DICT_SIZE_ERROR(); |
| 1441 | } |
| 1442 | |
| 1443 | istream_t in = IO_make_istream(byte_src, src_len); |
| 1444 | |
| 1445 | const u32 magic_number = IO_read_bits(&in, 32); |
| 1446 | if (magic_number != 0xEC30A437) { |
| 1447 | // raw content dict |
| 1448 | IO_rewind_bits(&in, 32); |
| 1449 | init_dictionary_content(dict, &in); |
| 1450 | return; |
| 1451 | } |
| 1452 | |
| 1453 | dict->dictionary_id = IO_read_bits(&in, 32); |
| 1454 | |
| 1455 | // "Entropy_Tables : following the same format as the tables in compressed |
| 1456 | // blocks. They are stored in following order : Huffman tables for literals, |
| 1457 | // FSE table for offsets, FSE table for match lengths, and FSE table for |
| 1458 | // literals lengths. It's finally followed by 3 offset values, populating |
| 1459 | // recent offsets (instead of using {1,4,8}), stored in order, 4-bytes |
| 1460 | // little-endian each, for a total of 12 bytes. Each recent offset must have |
| 1461 | // a value < dictionary size." |
| 1462 | decode_huf_table(&dict->literals_dtable, &in); |
| 1463 | decode_seq_table(&dict->of_dtable, &in, seq_offset, seq_fse); |
| 1464 | decode_seq_table(&dict->ml_dtable, &in, seq_match_length, seq_fse); |
| 1465 | decode_seq_table(&dict->ll_dtable, &in, seq_literal_length, seq_fse); |
| 1466 | |
| 1467 | // Read in the previous offset history |
| 1468 | dict->previous_offsets[0] = IO_read_bits(&in, 32); |
| 1469 | dict->previous_offsets[1] = IO_read_bits(&in, 32); |
| 1470 | dict->previous_offsets[2] = IO_read_bits(&in, 32); |
| 1471 | |
| 1472 | // Ensure the provided offsets aren't too large |
| 1473 | // "Each recent offset must have a value < dictionary size." |
| 1474 | for (int i = 0; i < 3; i++) { |
| 1475 | if (dict->previous_offsets[i] > src_len) { |
| 1476 | ERROR("Dictionary corrupted"); |
| 1477 | } |
| 1478 | } |
| 1479 | |
| 1480 | // "Content : The rest of the dictionary is its content. The content act as |
| 1481 | // a "past" in front of data to compress or decompress, so it can be |
| 1482 | // referenced in sequence commands." |
| 1483 | init_dictionary_content(dict, &in); |
| 1484 | } |
| 1485 | |
| 1486 | static void init_dictionary_content(dictionary_t *const dict, |
| 1487 | istream_t *const in) { |
| 1488 | // Copy in the content |
| 1489 | dict->content_size = IO_istream_len(in); |
| 1490 | dict->content = malloc(dict->content_size); |
| 1491 | if (!dict->content) { |
| 1492 | BAD_ALLOC(); |
| 1493 | } |
| 1494 | |
| 1495 | const u8 *const content = IO_get_read_ptr(in, dict->content_size); |
| 1496 | |
| 1497 | memcpy(dict->content, content, dict->content_size); |
| 1498 | } |
| 1499 | |
| 1500 | static void HUF_copy_dtable(HUF_dtable *const dst, |
| 1501 | const HUF_dtable *const src) { |
| 1502 | if (src->max_bits == 0) { |
| 1503 | memset(dst, 0, sizeof(HUF_dtable)); |
| 1504 | return; |
| 1505 | } |
| 1506 | |
| 1507 | const size_t size = (size_t)1 << src->max_bits; |
| 1508 | dst->max_bits = src->max_bits; |
| 1509 | |
| 1510 | dst->symbols = malloc(size); |
| 1511 | dst->num_bits = malloc(size); |
| 1512 | if (!dst->symbols || !dst->num_bits) { |
| 1513 | BAD_ALLOC(); |
| 1514 | } |
| 1515 | |
| 1516 | memcpy(dst->symbols, src->symbols, size); |
| 1517 | memcpy(dst->num_bits, src->num_bits, size); |
| 1518 | } |
| 1519 | |
| 1520 | static void FSE_copy_dtable(FSE_dtable *const dst, const FSE_dtable *const src) { |
| 1521 | if (src->accuracy_log == 0) { |
| 1522 | memset(dst, 0, sizeof(FSE_dtable)); |
| 1523 | return; |
| 1524 | } |
| 1525 | |
| 1526 | size_t size = (size_t)1 << src->accuracy_log; |
| 1527 | dst->accuracy_log = src->accuracy_log; |
| 1528 | |
| 1529 | dst->symbols = malloc(size); |
| 1530 | dst->num_bits = malloc(size); |
| 1531 | dst->new_state_base = malloc(size * sizeof(u16)); |
| 1532 | if (!dst->symbols || !dst->num_bits || !dst->new_state_base) { |
| 1533 | BAD_ALLOC(); |
| 1534 | } |
| 1535 | |
| 1536 | memcpy(dst->symbols, src->symbols, size); |
| 1537 | memcpy(dst->num_bits, src->num_bits, size); |
| 1538 | memcpy(dst->new_state_base, src->new_state_base, size * sizeof(u16)); |
| 1539 | } |
| 1540 | |
| 1541 | /// A dictionary acts as initializing values for the frame context before |
| 1542 | /// decompression, so we implement it by applying it's predetermined |
| 1543 | /// tables and content to the context before beginning decompression |
| 1544 | static void frame_context_apply_dict(frame_context_t *const ctx, |
| 1545 | const dictionary_t *const dict) { |
| 1546 | // If the content pointer is NULL then it must be an empty dict |
| 1547 | if (!dict || !dict->content) |
| 1548 | return; |
| 1549 | |
| 1550 | // If the requested dictionary_id is non-zero, the correct dictionary must |
| 1551 | // be present |
| 1552 | if (ctx->header.dictionary_id != 0 && |
| 1553 | ctx->header.dictionary_id != dict->dictionary_id) { |
| 1554 | ERROR("Wrong dictionary provided"); |
| 1555 | } |
| 1556 | |
| 1557 | // Copy the dict content to the context for references during sequence |
| 1558 | // execution |
| 1559 | ctx->dict_content = dict->content; |
| 1560 | ctx->dict_content_len = dict->content_size; |
| 1561 | |
| 1562 | // If it's a formatted dict copy the precomputed tables in so they can |
| 1563 | // be used in the table repeat modes |
| 1564 | if (dict->dictionary_id != 0) { |
| 1565 | // Deep copy the entropy tables so they can be freed independently of |
| 1566 | // the dictionary struct |
| 1567 | HUF_copy_dtable(&ctx->literals_dtable, &dict->literals_dtable); |
| 1568 | FSE_copy_dtable(&ctx->ll_dtable, &dict->ll_dtable); |
| 1569 | FSE_copy_dtable(&ctx->of_dtable, &dict->of_dtable); |
| 1570 | FSE_copy_dtable(&ctx->ml_dtable, &dict->ml_dtable); |
| 1571 | |
| 1572 | // Copy the repeated offsets |
| 1573 | memcpy(ctx->previous_offsets, dict->previous_offsets, |
| 1574 | sizeof(ctx->previous_offsets)); |
| 1575 | } |
| 1576 | } |
| 1577 | |
| 1578 | #else // ZDEC_NO_DICTIONARY is defined |
| 1579 | |
| 1580 | static void frame_context_apply_dict(frame_context_t *const ctx, |
| 1581 | const dictionary_t *const dict) { |
| 1582 | (void)ctx; |
| 1583 | if (dict && dict->content) ERROR("dictionary not supported"); |
| 1584 | } |
| 1585 | |
| 1586 | #endif |
| 1587 | /******* END DICTIONARY PARSING ***********************************************/ |
| 1588 | |
| 1589 | /******* IO STREAM OPERATIONS *************************************************/ |
| 1590 | |
| 1591 | /// Reads `num` bits from a bitstream, and updates the internal offset |
| 1592 | static inline u64 IO_read_bits(istream_t *const in, const int num_bits) { |
| 1593 | if (num_bits > 64 || num_bits <= 0) { |
| 1594 | ERROR("Attempt to read an invalid number of bits"); |
| 1595 | } |
| 1596 | |
| 1597 | const size_t bytes = (num_bits + in->bit_offset + 7) / 8; |
| 1598 | const size_t full_bytes = (num_bits + in->bit_offset) / 8; |
| 1599 | if (bytes > in->len) { |
| 1600 | INP_SIZE(); |
| 1601 | } |
| 1602 | |
| 1603 | const u64 result = read_bits_LE(in->ptr, num_bits, in->bit_offset); |
| 1604 | |
| 1605 | in->bit_offset = (num_bits + in->bit_offset) % 8; |
| 1606 | in->ptr += full_bytes; |
| 1607 | in->len -= full_bytes; |
| 1608 | |
| 1609 | return result; |
| 1610 | } |
| 1611 | |
| 1612 | /// If a non-zero number of bits have been read from the current byte, advance |
| 1613 | /// the offset to the next byte |
| 1614 | static inline void IO_rewind_bits(istream_t *const in, int num_bits) { |
| 1615 | if (num_bits < 0) { |
| 1616 | ERROR("Attempting to rewind stream by a negative number of bits"); |
| 1617 | } |
| 1618 | |
| 1619 | // move the offset back by `num_bits` bits |
| 1620 | const int new_offset = in->bit_offset - num_bits; |
| 1621 | // determine the number of whole bytes we have to rewind, rounding up to an |
| 1622 | // integer number (e.g. if `new_offset == -5`, `bytes == 1`) |
| 1623 | const i64 bytes = -(new_offset - 7) / 8; |
| 1624 | |
| 1625 | in->ptr -= bytes; |
| 1626 | in->len += bytes; |
| 1627 | // make sure the resulting `bit_offset` is positive, as mod in C does not |
| 1628 | // convert numbers from negative to positive (e.g. -22 % 8 == -6) |
| 1629 | in->bit_offset = ((new_offset % 8) + 8) % 8; |
| 1630 | } |
| 1631 | |
| 1632 | /// If the remaining bits in a byte will be unused, advance to the end of the |
| 1633 | /// byte |
| 1634 | static inline void IO_align_stream(istream_t *const in) { |
| 1635 | if (in->bit_offset != 0) { |
| 1636 | if (in->len == 0) { |
| 1637 | INP_SIZE(); |
| 1638 | } |
| 1639 | in->ptr++; |
| 1640 | in->len--; |
| 1641 | in->bit_offset = 0; |
| 1642 | } |
| 1643 | } |
| 1644 | |
| 1645 | /// Write the given byte into the output stream |
| 1646 | static inline void IO_write_byte(ostream_t *const out, u8 symb) { |
| 1647 | if (out->len == 0) { |
| 1648 | OUT_SIZE(); |
| 1649 | } |
| 1650 | |
| 1651 | out->ptr[0] = symb; |
| 1652 | out->ptr++; |
| 1653 | out->len--; |
| 1654 | } |
| 1655 | |
| 1656 | /// Returns the number of bytes left to be read in this stream. The stream must |
| 1657 | /// be byte aligned. |
| 1658 | static inline size_t IO_istream_len(const istream_t *const in) { |
| 1659 | return in->len; |
| 1660 | } |
| 1661 | |
| 1662 | /// Returns a pointer where `len` bytes can be read, and advances the internal |
| 1663 | /// state. The stream must be byte aligned. |
| 1664 | static inline const u8 *IO_get_read_ptr(istream_t *const in, size_t len) { |
| 1665 | if (len > in->len) { |
| 1666 | INP_SIZE(); |
| 1667 | } |
| 1668 | if (in->bit_offset != 0) { |
| 1669 | ERROR("Attempting to operate on a non-byte aligned stream"); |
| 1670 | } |
| 1671 | const u8 *const ptr = in->ptr; |
| 1672 | in->ptr += len; |
| 1673 | in->len -= len; |
| 1674 | |
| 1675 | return ptr; |
| 1676 | } |
| 1677 | /// Returns a pointer to write `len` bytes to, and advances the internal state |
| 1678 | static inline u8 *IO_get_write_ptr(ostream_t *const out, size_t len) { |
| 1679 | if (len > out->len) { |
| 1680 | OUT_SIZE(); |
| 1681 | } |
| 1682 | u8 *const ptr = out->ptr; |
| 1683 | out->ptr += len; |
| 1684 | out->len -= len; |
| 1685 | |
| 1686 | return ptr; |
| 1687 | } |
| 1688 | |
| 1689 | /// Advance the inner state by `len` bytes |
| 1690 | static inline void IO_advance_input(istream_t *const in, size_t len) { |
| 1691 | if (len > in->len) { |
| 1692 | INP_SIZE(); |
| 1693 | } |
| 1694 | if (in->bit_offset != 0) { |
| 1695 | ERROR("Attempting to operate on a non-byte aligned stream"); |
| 1696 | } |
| 1697 | |
| 1698 | in->ptr += len; |
| 1699 | in->len -= len; |
| 1700 | } |
| 1701 | |
| 1702 | /// Returns an `ostream_t` constructed from the given pointer and length |
| 1703 | static inline ostream_t IO_make_ostream(u8 *out, size_t len) { |
| 1704 | return (ostream_t) { out, len }; |
| 1705 | } |
| 1706 | |
| 1707 | /// Returns an `istream_t` constructed from the given pointer and length |
| 1708 | static inline istream_t IO_make_istream(const u8 *in, size_t len) { |
| 1709 | return (istream_t) { in, len, 0 }; |
| 1710 | } |
| 1711 | |
| 1712 | /// Returns an `istream_t` with the same base as `in`, and length `len` |
| 1713 | /// Then, advance `in` to account for the consumed bytes |
| 1714 | /// `in` must be byte aligned |
| 1715 | static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len) { |
| 1716 | // Consume `len` bytes of the parent stream |
| 1717 | const u8 *const ptr = IO_get_read_ptr(in, len); |
| 1718 | |
| 1719 | // Make a substream using the pointer to those `len` bytes |
| 1720 | return IO_make_istream(ptr, len); |
| 1721 | } |
| 1722 | /******* END IO STREAM OPERATIONS *********************************************/ |
| 1723 | |
| 1724 | /******* BITSTREAM OPERATIONS *************************************************/ |
| 1725 | /// Read `num` bits (up to 64) from `src + offset`, where `offset` is in bits |
| 1726 | static inline u64 read_bits_LE(const u8 *src, const int num_bits, |
| 1727 | const size_t offset) { |
| 1728 | if (num_bits > 64) { |
| 1729 | ERROR("Attempt to read an invalid number of bits"); |
| 1730 | } |
| 1731 | |
| 1732 | // Skip over bytes that aren't in range |
| 1733 | src += offset / 8; |
| 1734 | size_t bit_offset = offset % 8; |
| 1735 | u64 res = 0; |
| 1736 | |
| 1737 | int shift = 0; |
| 1738 | int left = num_bits; |
| 1739 | while (left > 0) { |
| 1740 | u64 mask = left >= 8 ? 0xff : (((u64)1 << left) - 1); |
| 1741 | // Read the next byte, shift it to account for the offset, and then mask |
| 1742 | // out the top part if we don't need all the bits |
| 1743 | res += (((u64)*src++ >> bit_offset) & mask) << shift; |
| 1744 | shift += 8 - bit_offset; |
| 1745 | left -= 8 - bit_offset; |
| 1746 | bit_offset = 0; |
| 1747 | } |
| 1748 | |
| 1749 | return res; |
| 1750 | } |
| 1751 | |
| 1752 | /// Read bits from the end of a HUF or FSE bitstream. `offset` is in bits, so |
| 1753 | /// it updates `offset` to `offset - bits`, and then reads `bits` bits from |
| 1754 | /// `src + offset`. If the offset becomes negative, the extra bits at the |
| 1755 | /// bottom are filled in with `0` bits instead of reading from before `src`. |
| 1756 | static inline u64 STREAM_read_bits(const u8 *const src, const int bits, |
| 1757 | i64 *const offset) { |
| 1758 | *offset = *offset - bits; |
| 1759 | size_t actual_off = *offset; |
| 1760 | size_t actual_bits = bits; |
| 1761 | // Don't actually read bits from before the start of src, so if `*offset < |
| 1762 | // 0` fix actual_off and actual_bits to reflect the quantity to read |
| 1763 | if (*offset < 0) { |
| 1764 | actual_bits += *offset; |
| 1765 | actual_off = 0; |
| 1766 | } |
| 1767 | u64 res = read_bits_LE(src, actual_bits, actual_off); |
| 1768 | |
| 1769 | if (*offset < 0) { |
| 1770 | // Fill in the bottom "overflowed" bits with 0's |
| 1771 | res = -*offset >= 64 ? 0 : (res << -*offset); |
| 1772 | } |
| 1773 | return res; |
| 1774 | } |
| 1775 | /******* END BITSTREAM OPERATIONS *********************************************/ |
| 1776 | |
| 1777 | /******* BIT COUNTING OPERATIONS **********************************************/ |
| 1778 | /// Returns `x`, where `2^x` is the largest power of 2 less than or equal to |
| 1779 | /// `num`, or `-1` if `num == 0`. |
| 1780 | static inline int highest_set_bit(const u64 num) { |
| 1781 | for (int i = 63; i >= 0; i--) { |
| 1782 | if (((u64)1 << i) <= num) { |
| 1783 | return i; |
| 1784 | } |
| 1785 | } |
| 1786 | return -1; |
| 1787 | } |
| 1788 | /******* END BIT COUNTING OPERATIONS ******************************************/ |
| 1789 | |
| 1790 | /******* HUFFMAN PRIMITIVES ***************************************************/ |
| 1791 | static inline u8 HUF_decode_symbol(const HUF_dtable *const dtable, |
| 1792 | u16 *const state, const u8 *const src, |
| 1793 | i64 *const offset) { |
| 1794 | // Look up the symbol and number of bits to read |
| 1795 | const u8 symb = dtable->symbols[*state]; |
| 1796 | const u8 bits = dtable->num_bits[*state]; |
| 1797 | const u16 rest = STREAM_read_bits(src, bits, offset); |
| 1798 | // Shift `bits` bits out of the state, keeping the low order bits that |
| 1799 | // weren't necessary to determine this symbol. Then add in the new bits |
| 1800 | // read from the stream. |
| 1801 | *state = ((*state << bits) + rest) & (((u16)1 << dtable->max_bits) - 1); |
| 1802 | |
| 1803 | return symb; |
| 1804 | } |
| 1805 | |
| 1806 | static inline void HUF_init_state(const HUF_dtable *const dtable, |
| 1807 | u16 *const state, const u8 *const src, |
| 1808 | i64 *const offset) { |
| 1809 | // Read in a full `dtable->max_bits` bits to initialize the state |
| 1810 | const u8 bits = dtable->max_bits; |
| 1811 | *state = STREAM_read_bits(src, bits, offset); |
| 1812 | } |
| 1813 | |
| 1814 | static size_t HUF_decompress_1stream(const HUF_dtable *const dtable, |
| 1815 | ostream_t *const out, |
| 1816 | istream_t *const in) { |
| 1817 | const size_t len = IO_istream_len(in); |
| 1818 | if (len == 0) { |
| 1819 | INP_SIZE(); |
| 1820 | } |
| 1821 | const u8 *const src = IO_get_read_ptr(in, len); |
| 1822 | |
| 1823 | // "Each bitstream must be read backward, that is starting from the end down |
| 1824 | // to the beginning. Therefore it's necessary to know the size of each |
| 1825 | // bitstream. |
| 1826 | // |
| 1827 | // It's also necessary to know exactly which bit is the latest. This is |
| 1828 | // detected by a final bit flag : the highest bit of latest byte is a |
| 1829 | // final-bit-flag. Consequently, a last byte of 0 is not possible. And the |
| 1830 | // final-bit-flag itself is not part of the useful bitstream. Hence, the |
| 1831 | // last byte contains between 0 and 7 useful bits." |
| 1832 | const int padding = 8 - highest_set_bit(src[len - 1]); |
| 1833 | |
| 1834 | // Offset starts at the end because HUF streams are read backwards |
| 1835 | i64 bit_offset = len * 8 - padding; |
| 1836 | u16 state; |
| 1837 | |
| 1838 | HUF_init_state(dtable, &state, src, &bit_offset); |
| 1839 | |
| 1840 | size_t symbols_written = 0; |
| 1841 | while (bit_offset > -dtable->max_bits) { |
| 1842 | // Iterate over the stream, decoding one symbol at a time |
| 1843 | IO_write_byte(out, HUF_decode_symbol(dtable, &state, src, &bit_offset)); |
| 1844 | symbols_written++; |
| 1845 | } |
| 1846 | // "The process continues up to reading the required number of symbols per |
| 1847 | // stream. If a bitstream is not entirely and exactly consumed, hence |
| 1848 | // reaching exactly its beginning position with all bits consumed, the |
| 1849 | // decoding process is considered faulty." |
| 1850 | |
| 1851 | // When all symbols have been decoded, the final state value shouldn't have |
| 1852 | // any data from the stream, so it should have "read" dtable->max_bits from |
| 1853 | // before the start of `src` |
| 1854 | // Therefore `offset`, the edge to start reading new bits at, should be |
| 1855 | // dtable->max_bits before the start of the stream |
| 1856 | if (bit_offset != -dtable->max_bits) { |
| 1857 | CORRUPTION(); |
| 1858 | } |
| 1859 | |
| 1860 | return symbols_written; |
| 1861 | } |
| 1862 | |
| 1863 | static size_t HUF_decompress_4stream(const HUF_dtable *const dtable, |
| 1864 | ostream_t *const out, istream_t *const in) { |
| 1865 | // "Compressed size is provided explicitly : in the 4-streams variant, |
| 1866 | // bitstreams are preceded by 3 unsigned little-endian 16-bits values. Each |
| 1867 | // value represents the compressed size of one stream, in order. The last |
| 1868 | // stream size is deducted from total compressed size and from previously |
| 1869 | // decoded stream sizes" |
| 1870 | const size_t csize1 = IO_read_bits(in, 16); |
| 1871 | const size_t csize2 = IO_read_bits(in, 16); |
| 1872 | const size_t csize3 = IO_read_bits(in, 16); |
| 1873 | |
| 1874 | istream_t in1 = IO_make_sub_istream(in, csize1); |
| 1875 | istream_t in2 = IO_make_sub_istream(in, csize2); |
| 1876 | istream_t in3 = IO_make_sub_istream(in, csize3); |
| 1877 | istream_t in4 = IO_make_sub_istream(in, IO_istream_len(in)); |
| 1878 | |
| 1879 | size_t total_output = 0; |
| 1880 | // Decode each stream independently for simplicity |
| 1881 | // If we wanted to we could decode all 4 at the same time for speed, |
| 1882 | // utilizing more execution units |
| 1883 | total_output += HUF_decompress_1stream(dtable, out, &in1); |
| 1884 | total_output += HUF_decompress_1stream(dtable, out, &in2); |
| 1885 | total_output += HUF_decompress_1stream(dtable, out, &in3); |
| 1886 | total_output += HUF_decompress_1stream(dtable, out, &in4); |
| 1887 | |
| 1888 | return total_output; |
| 1889 | } |
| 1890 | |
| 1891 | /// Initializes a Huffman table using canonical Huffman codes |
| 1892 | /// For more explanation on canonical Huffman codes see |
| 1893 | /// https://www.cs.scranton.edu/~mccloske/courses/cmps340/huff_canonical_dec2015.html |
| 1894 | /// Codes within a level are allocated in symbol order (i.e. smaller symbols get |
| 1895 | /// earlier codes) |
| 1896 | static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, |
| 1897 | const int num_symbs) { |
| 1898 | memset(table, 0, sizeof(HUF_dtable)); |
| 1899 | if (num_symbs > HUF_MAX_SYMBS) { |
| 1900 | ERROR("Too many symbols for Huffman"); |
| 1901 | } |
| 1902 | |
| 1903 | u8 max_bits = 0; |
| 1904 | u16 rank_count[HUF_MAX_BITS + 1]; |
| 1905 | memset(rank_count, 0, sizeof(rank_count)); |
| 1906 | |
| 1907 | // Count the number of symbols for each number of bits, and determine the |
| 1908 | // depth of the tree |
| 1909 | for (int i = 0; i < num_symbs; i++) { |
| 1910 | if (bits[i] > HUF_MAX_BITS) { |
| 1911 | ERROR("Huffman table depth too large"); |
| 1912 | } |
| 1913 | max_bits = MAX(max_bits, bits[i]); |
| 1914 | rank_count[bits[i]]++; |
| 1915 | } |
| 1916 | |
| 1917 | const size_t table_size = 1 << max_bits; |
| 1918 | table->max_bits = max_bits; |
| 1919 | table->symbols = malloc(table_size); |
| 1920 | table->num_bits = malloc(table_size); |
| 1921 | |
| 1922 | if (!table->symbols || !table->num_bits) { |
| 1923 | free(table->symbols); |
| 1924 | free(table->num_bits); |
| 1925 | BAD_ALLOC(); |
| 1926 | } |
| 1927 | |
| 1928 | // "Symbols are sorted by Weight. Within same Weight, symbols keep natural |
| 1929 | // order. Symbols with a Weight of zero are removed. Then, starting from |
| 1930 | // lowest weight, prefix codes are distributed in order." |
| 1931 | |
| 1932 | u32 rank_idx[HUF_MAX_BITS + 1]; |
| 1933 | // Initialize the starting codes for each rank (number of bits) |
| 1934 | rank_idx[max_bits] = 0; |
| 1935 | for (int i = max_bits; i >= 1; i--) { |
| 1936 | rank_idx[i - 1] = rank_idx[i] + rank_count[i] * (1 << (max_bits - i)); |
| 1937 | // The entire range takes the same number of bits so we can memset it |
| 1938 | memset(&table->num_bits[rank_idx[i]], i, rank_idx[i - 1] - rank_idx[i]); |
| 1939 | } |
| 1940 | |
| 1941 | if (rank_idx[0] != table_size) { |
| 1942 | CORRUPTION(); |
| 1943 | } |
| 1944 | |
| 1945 | // Allocate codes and fill in the table |
| 1946 | for (int i = 0; i < num_symbs; i++) { |
| 1947 | if (bits[i] != 0) { |
| 1948 | // Allocate a code for this symbol and set its range in the table |
| 1949 | const u16 code = rank_idx[bits[i]]; |
| 1950 | // Since the code doesn't care about the bottom `max_bits - bits[i]` |
| 1951 | // bits of state, it gets a range that spans all possible values of |
| 1952 | // the lower bits |
| 1953 | const u16 len = 1 << (max_bits - bits[i]); |
| 1954 | memset(&table->symbols[code], i, len); |
| 1955 | rank_idx[bits[i]] += len; |
| 1956 | } |
| 1957 | } |
| 1958 | } |
| 1959 | |
| 1960 | static void HUF_init_dtable_usingweights(HUF_dtable *const table, |
| 1961 | const u8 *const weights, |
| 1962 | const int num_symbs) { |
| 1963 | // +1 because the last weight is not transmitted in the header |
| 1964 | if (num_symbs + 1 > HUF_MAX_SYMBS) { |
| 1965 | ERROR("Too many symbols for Huffman"); |
| 1966 | } |
| 1967 | |
| 1968 | u8 bits[HUF_MAX_SYMBS]; |
| 1969 | |
| 1970 | u64 weight_sum = 0; |
| 1971 | for (int i = 0; i < num_symbs; i++) { |
| 1972 | // Weights are in the same range as bit count |
| 1973 | if (weights[i] > HUF_MAX_BITS) { |
| 1974 | CORRUPTION(); |
| 1975 | } |
| 1976 | weight_sum += weights[i] > 0 ? (u64)1 << (weights[i] - 1) : 0; |
| 1977 | } |
| 1978 | |
| 1979 | // Find the first power of 2 larger than the sum |
| 1980 | const int max_bits = highest_set_bit(weight_sum) + 1; |
| 1981 | const u64 left_over = ((u64)1 << max_bits) - weight_sum; |
| 1982 | // If the left over isn't a power of 2, the weights are invalid |
| 1983 | if (left_over & (left_over - 1)) { |
| 1984 | CORRUPTION(); |
| 1985 | } |
| 1986 | |
| 1987 | // left_over is used to find the last weight as it's not transmitted |
| 1988 | // by inverting 2^(weight - 1) we can determine the value of last_weight |
| 1989 | const int last_weight = highest_set_bit(left_over) + 1; |
| 1990 | |
| 1991 | for (int i = 0; i < num_symbs; i++) { |
| 1992 | // "Number_of_Bits = Number_of_Bits ? Max_Number_of_Bits + 1 - Weight : 0" |
| 1993 | bits[i] = weights[i] > 0 ? (max_bits + 1 - weights[i]) : 0; |
| 1994 | } |
| 1995 | bits[num_symbs] = |
| 1996 | max_bits + 1 - last_weight; // Last weight is always non-zero |
| 1997 | |
| 1998 | HUF_init_dtable(table, bits, num_symbs + 1); |
| 1999 | } |
| 2000 | |
| 2001 | static void HUF_free_dtable(HUF_dtable *const dtable) { |
| 2002 | free(dtable->symbols); |
| 2003 | free(dtable->num_bits); |
| 2004 | memset(dtable, 0, sizeof(HUF_dtable)); |
| 2005 | } |
| 2006 | /******* END HUFFMAN PRIMITIVES ***********************************************/ |
| 2007 | |
| 2008 | /******* FSE PRIMITIVES *******************************************************/ |
| 2009 | /// For more description of FSE see |
| 2010 | /// https://github.com/Cyan4973/FiniteStateEntropy/ |
| 2011 | |
| 2012 | /// Allow a symbol to be decoded without updating state |
| 2013 | static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, |
| 2014 | const u16 state) { |
| 2015 | return dtable->symbols[state]; |
| 2016 | } |
| 2017 | |
| 2018 | /// Consumes bits from the input and uses the current state to determine the |
| 2019 | /// next state |
| 2020 | static inline void FSE_update_state(const FSE_dtable *const dtable, |
| 2021 | u16 *const state, const u8 *const src, |
| 2022 | i64 *const offset) { |
| 2023 | const u8 bits = dtable->num_bits[*state]; |
| 2024 | const u16 rest = STREAM_read_bits(src, bits, offset); |
| 2025 | *state = dtable->new_state_base[*state] + rest; |
| 2026 | } |
| 2027 | |
| 2028 | /// Decodes a single FSE symbol and updates the offset |
| 2029 | static inline u8 FSE_decode_symbol(const FSE_dtable *const dtable, |
| 2030 | u16 *const state, const u8 *const src, |
| 2031 | i64 *const offset) { |
| 2032 | const u8 symb = FSE_peek_symbol(dtable, *state); |
| 2033 | FSE_update_state(dtable, state, src, offset); |
| 2034 | return symb; |
| 2035 | } |
| 2036 | |
| 2037 | static inline void FSE_init_state(const FSE_dtable *const dtable, |
| 2038 | u16 *const state, const u8 *const src, |
| 2039 | i64 *const offset) { |
| 2040 | // Read in a full `accuracy_log` bits to initialize the state |
| 2041 | const u8 bits = dtable->accuracy_log; |
| 2042 | *state = STREAM_read_bits(src, bits, offset); |
| 2043 | } |
| 2044 | |
| 2045 | static size_t FSE_decompress_interleaved2(const FSE_dtable *const dtable, |
| 2046 | ostream_t *const out, |
| 2047 | istream_t *const in) { |
| 2048 | const size_t len = IO_istream_len(in); |
| 2049 | if (len == 0) { |
| 2050 | INP_SIZE(); |
| 2051 | } |
| 2052 | const u8 *const src = IO_get_read_ptr(in, len); |
| 2053 | |
| 2054 | // "Each bitstream must be read backward, that is starting from the end down |
| 2055 | // to the beginning. Therefore it's necessary to know the size of each |
| 2056 | // bitstream. |
| 2057 | // |
| 2058 | // It's also necessary to know exactly which bit is the latest. This is |
| 2059 | // detected by a final bit flag : the highest bit of latest byte is a |
| 2060 | // final-bit-flag. Consequently, a last byte of 0 is not possible. And the |
| 2061 | // final-bit-flag itself is not part of the useful bitstream. Hence, the |
| 2062 | // last byte contains between 0 and 7 useful bits." |
| 2063 | const int padding = 8 - highest_set_bit(src[len - 1]); |
| 2064 | i64 offset = len * 8 - padding; |
| 2065 | |
| 2066 | u16 state1, state2; |
| 2067 | // "The first state (State1) encodes the even indexed symbols, and the |
| 2068 | // second (State2) encodes the odd indexes. State1 is initialized first, and |
| 2069 | // then State2, and they take turns decoding a single symbol and updating |
| 2070 | // their state." |
| 2071 | FSE_init_state(dtable, &state1, src, &offset); |
| 2072 | FSE_init_state(dtable, &state2, src, &offset); |
| 2073 | |
| 2074 | // Decode until we overflow the stream |
| 2075 | // Since we decode in reverse order, overflowing the stream is offset going |
| 2076 | // negative |
| 2077 | size_t symbols_written = 0; |
| 2078 | while (1) { |
| 2079 | // "The number of symbols to decode is determined by tracking bitStream |
| 2080 | // overflow condition: If updating state after decoding a symbol would |
| 2081 | // require more bits than remain in the stream, it is assumed the extra |
| 2082 | // bits are 0. Then, the symbols for each of the final states are |
| 2083 | // decoded and the process is complete." |
| 2084 | IO_write_byte(out, FSE_decode_symbol(dtable, &state1, src, &offset)); |
| 2085 | symbols_written++; |
| 2086 | if (offset < 0) { |
| 2087 | // There's still a symbol to decode in state2 |
| 2088 | IO_write_byte(out, FSE_peek_symbol(dtable, state2)); |
| 2089 | symbols_written++; |
| 2090 | break; |
| 2091 | } |
| 2092 | |
| 2093 | IO_write_byte(out, FSE_decode_symbol(dtable, &state2, src, &offset)); |
| 2094 | symbols_written++; |
| 2095 | if (offset < 0) { |
| 2096 | // There's still a symbol to decode in state1 |
| 2097 | IO_write_byte(out, FSE_peek_symbol(dtable, state1)); |
| 2098 | symbols_written++; |
| 2099 | break; |
| 2100 | } |
| 2101 | } |
| 2102 | |
| 2103 | return symbols_written; |
| 2104 | } |
| 2105 | |
| 2106 | static void FSE_init_dtable(FSE_dtable *const dtable, |
| 2107 | const i16 *const norm_freqs, const int num_symbs, |
| 2108 | const int accuracy_log) { |
| 2109 | if (accuracy_log > FSE_MAX_ACCURACY_LOG) { |
| 2110 | ERROR("FSE accuracy too large"); |
| 2111 | } |
| 2112 | if (num_symbs > FSE_MAX_SYMBS) { |
| 2113 | ERROR("Too many symbols for FSE"); |
| 2114 | } |
| 2115 | |
| 2116 | dtable->accuracy_log = accuracy_log; |
| 2117 | |
| 2118 | const size_t size = (size_t)1 << accuracy_log; |
| 2119 | dtable->symbols = malloc(size * sizeof(u8)); |
| 2120 | dtable->num_bits = malloc(size * sizeof(u8)); |
| 2121 | dtable->new_state_base = malloc(size * sizeof(u16)); |
| 2122 | |
| 2123 | if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { |
| 2124 | BAD_ALLOC(); |
| 2125 | } |
| 2126 | |
| 2127 | // Used to determine how many bits need to be read for each state, |
| 2128 | // and where the destination range should start |
| 2129 | // Needs to be u16 because max value is 2 * max number of symbols, |
| 2130 | // which can be larger than a byte can store |
| 2131 | u16 state_desc[FSE_MAX_SYMBS]; |
| 2132 | |
| 2133 | // "Symbols are scanned in their natural order for "less than 1" |
| 2134 | // probabilities. Symbols with this probability are being attributed a |
| 2135 | // single cell, starting from the end of the table. These symbols define a |
| 2136 | // full state reset, reading Accuracy_Log bits." |
| 2137 | int high_threshold = size; |
| 2138 | for (int s = 0; s < num_symbs; s++) { |
| 2139 | // Scan for low probability symbols to put at the top |
| 2140 | if (norm_freqs[s] == -1) { |
| 2141 | dtable->symbols[--high_threshold] = s; |
| 2142 | state_desc[s] = 1; |
| 2143 | } |
| 2144 | } |
| 2145 | |
| 2146 | // "All remaining symbols are sorted in their natural order. Starting from |
| 2147 | // symbol 0 and table position 0, each symbol gets attributed as many cells |
| 2148 | // as its probability. Cell allocation is spread, not linear." |
| 2149 | // Place the rest in the table |
| 2150 | const u16 step = (size >> 1) + (size >> 3) + 3; |
| 2151 | const u16 mask = size - 1; |
| 2152 | u16 pos = 0; |
| 2153 | for (int s = 0; s < num_symbs; s++) { |
| 2154 | if (norm_freqs[s] <= 0) { |
| 2155 | continue; |
| 2156 | } |
| 2157 | |
| 2158 | state_desc[s] = norm_freqs[s]; |
| 2159 | |
| 2160 | for (int i = 0; i < norm_freqs[s]; i++) { |
| 2161 | // Give `norm_freqs[s]` states to symbol s |
| 2162 | dtable->symbols[pos] = s; |
| 2163 | // "A position is skipped if already occupied, typically by a "less |
| 2164 | // than 1" probability symbol." |
| 2165 | do { |
| 2166 | pos = (pos + step) & mask; |
| 2167 | } while (pos >= |
| 2168 | high_threshold); |
| 2169 | // Note: no other collision checking is necessary as `step` is |
| 2170 | // coprime to `size`, so the cycle will visit each position exactly |
| 2171 | // once |
| 2172 | } |
| 2173 | } |
| 2174 | if (pos != 0) { |
| 2175 | CORRUPTION(); |
| 2176 | } |
| 2177 | |
| 2178 | // Now we can fill baseline and num bits |
| 2179 | for (size_t i = 0; i < size; i++) { |
| 2180 | u8 symbol = dtable->symbols[i]; |
| 2181 | u16 next_state_desc = state_desc[symbol]++; |
| 2182 | // Fills in the table appropriately, next_state_desc increases by symbol |
| 2183 | // over time, decreasing number of bits |
| 2184 | dtable->num_bits[i] = (u8)(accuracy_log - highest_set_bit(next_state_desc)); |
| 2185 | // Baseline increases until the bit threshold is passed, at which point |
| 2186 | // it resets to 0 |
| 2187 | dtable->new_state_base[i] = |
| 2188 | ((u16)next_state_desc << dtable->num_bits[i]) - size; |
| 2189 | } |
| 2190 | } |
| 2191 | |
| 2192 | /// Decode an FSE header as defined in the Zstandard format specification and |
| 2193 | /// use the decoded frequencies to initialize a decoding table. |
| 2194 | static void FSE_decode_header(FSE_dtable *const dtable, istream_t *const in, |
| 2195 | const int max_accuracy_log) { |
| 2196 | // "An FSE distribution table describes the probabilities of all symbols |
| 2197 | // from 0 to the last present one (included) on a normalized scale of 1 << |
| 2198 | // Accuracy_Log . |
| 2199 | // |
| 2200 | // It's a bitstream which is read forward, in little-endian fashion. It's |
| 2201 | // not necessary to know its exact size, since it will be discovered and |
| 2202 | // reported by the decoding process. |
| 2203 | if (max_accuracy_log > FSE_MAX_ACCURACY_LOG) { |
| 2204 | ERROR("FSE accuracy too large"); |
| 2205 | } |
| 2206 | |
| 2207 | // The bitstream starts by reporting on which scale it operates. |
| 2208 | // Accuracy_Log = low4bits + 5. Note that maximum Accuracy_Log for literal |
| 2209 | // and match lengths is 9, and for offsets is 8. Higher values are |
| 2210 | // considered errors." |
| 2211 | const int accuracy_log = 5 + IO_read_bits(in, 4); |
| 2212 | if (accuracy_log > max_accuracy_log) { |
| 2213 | ERROR("FSE accuracy too large"); |
| 2214 | } |
| 2215 | |
| 2216 | // "Then follows each symbol value, from 0 to last present one. The number |
| 2217 | // of bits used by each field is variable. It depends on : |
| 2218 | // |
| 2219 | // Remaining probabilities + 1 : example : Presuming an Accuracy_Log of 8, |
| 2220 | // and presuming 100 probabilities points have already been distributed, the |
| 2221 | // decoder may read any value from 0 to 255 - 100 + 1 == 156 (inclusive). |
| 2222 | // Therefore, it must read log2sup(156) == 8 bits. |
| 2223 | // |
| 2224 | // Value decoded : small values use 1 less bit : example : Presuming values |
| 2225 | // from 0 to 156 (inclusive) are possible, 255-156 = 99 values are remaining |
| 2226 | // in an 8-bits field. They are used this way : first 99 values (hence from |
| 2227 | // 0 to 98) use only 7 bits, values from 99 to 156 use 8 bits. " |
| 2228 | |
| 2229 | i32 remaining = 1 << accuracy_log; |
| 2230 | i16 frequencies[FSE_MAX_SYMBS]; |
| 2231 | |
| 2232 | int symb = 0; |
| 2233 | while (remaining > 0 && symb < FSE_MAX_SYMBS) { |
| 2234 | // Log of the number of possible values we could read |
| 2235 | int bits = highest_set_bit(remaining + 1) + 1; |
| 2236 | |
| 2237 | u16 val = IO_read_bits(in, bits); |
| 2238 | |
| 2239 | // Try to mask out the lower bits to see if it qualifies for the "small |
| 2240 | // value" threshold |
| 2241 | const u16 lower_mask = ((u16)1 << (bits - 1)) - 1; |
| 2242 | const u16 threshold = ((u16)1 << bits) - 1 - (remaining + 1); |
| 2243 | |
| 2244 | if ((val & lower_mask) < threshold) { |
| 2245 | IO_rewind_bits(in, 1); |
| 2246 | val = val & lower_mask; |
| 2247 | } else if (val > lower_mask) { |
| 2248 | val = val - threshold; |
| 2249 | } |
| 2250 | |
| 2251 | // "Probability is obtained from Value decoded by following formula : |
| 2252 | // Proba = value - 1" |
| 2253 | const i16 proba = (i16)val - 1; |
| 2254 | |
| 2255 | // "It means value 0 becomes negative probability -1. -1 is a special |
| 2256 | // probability, which means "less than 1". Its effect on distribution |
| 2257 | // table is described in next paragraph. For the purpose of calculating |
| 2258 | // cumulated distribution, it counts as one." |
| 2259 | remaining -= proba < 0 ? -proba : proba; |
| 2260 | |
| 2261 | frequencies[symb] = proba; |
| 2262 | symb++; |
| 2263 | |
| 2264 | // "When a symbol has a probability of zero, it is followed by a 2-bits |
| 2265 | // repeat flag. This repeat flag tells how many probabilities of zeroes |
| 2266 | // follow the current one. It provides a number ranging from 0 to 3. If |
| 2267 | // it is a 3, another 2-bits repeat flag follows, and so on." |
| 2268 | if (proba == 0) { |
| 2269 | // Read the next two bits to see how many more 0s |
| 2270 | int repeat = IO_read_bits(in, 2); |
| 2271 | |
| 2272 | while (1) { |
| 2273 | for (int i = 0; i < repeat && symb < FSE_MAX_SYMBS; i++) { |
| 2274 | frequencies[symb++] = 0; |
| 2275 | } |
| 2276 | if (repeat == 3) { |
| 2277 | repeat = IO_read_bits(in, 2); |
| 2278 | } else { |
| 2279 | break; |
| 2280 | } |
| 2281 | } |
| 2282 | } |
| 2283 | } |
| 2284 | IO_align_stream(in); |
| 2285 | |
| 2286 | // "When last symbol reaches cumulated total of 1 << Accuracy_Log, decoding |
| 2287 | // is complete. If the last symbol makes cumulated total go above 1 << |
| 2288 | // Accuracy_Log, distribution is considered corrupted." |
| 2289 | if (remaining != 0 || symb >= FSE_MAX_SYMBS) { |
| 2290 | CORRUPTION(); |
| 2291 | } |
| 2292 | |
| 2293 | // Initialize the decoding table using the determined weights |
| 2294 | FSE_init_dtable(dtable, frequencies, symb, accuracy_log); |
| 2295 | } |
| 2296 | |
| 2297 | static void FSE_init_dtable_rle(FSE_dtable *const dtable, const u8 symb) { |
| 2298 | dtable->symbols = malloc(sizeof(u8)); |
| 2299 | dtable->num_bits = malloc(sizeof(u8)); |
| 2300 | dtable->new_state_base = malloc(sizeof(u16)); |
| 2301 | |
| 2302 | if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { |
| 2303 | BAD_ALLOC(); |
| 2304 | } |
| 2305 | |
| 2306 | // This setup will always have a state of 0, always return symbol `symb`, |
| 2307 | // and never consume any bits |
| 2308 | dtable->symbols[0] = symb; |
| 2309 | dtable->num_bits[0] = 0; |
| 2310 | dtable->new_state_base[0] = 0; |
| 2311 | dtable->accuracy_log = 0; |
| 2312 | } |
| 2313 | |
| 2314 | static void FSE_free_dtable(FSE_dtable *const dtable) { |
| 2315 | free(dtable->symbols); |
| 2316 | free(dtable->num_bits); |
| 2317 | free(dtable->new_state_base); |
| 2318 | memset(dtable, 0, sizeof(FSE_dtable)); |
| 2319 | } |
| 2320 | /******* END FSE PRIMITIVES ***************************************************/ |