648db22b |
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, |
f535537f |
1000 | i64 *const offset, |
1001 | int lastSequence); |
648db22b |
1002 | static void decode_seq_table(FSE_dtable *const table, istream_t *const in, |
1003 | const seq_part_t type, const seq_mode_t mode); |
1004 | |
1005 | static size_t decode_sequences(frame_context_t *const ctx, istream_t *in, |
1006 | sequence_command_t **const sequences) { |
1007 | // "A compressed block is a succession of sequences . A sequence is a |
1008 | // literal copy command, followed by a match copy command. A literal copy |
1009 | // command specifies a length. It is the number of bytes to be copied (or |
1010 | // extracted) from the literal section. A match copy command specifies an |
1011 | // offset and a length. The offset gives the position to copy from, which |
1012 | // can be within a previous block." |
1013 | |
1014 | size_t num_sequences; |
1015 | |
1016 | // "Number_of_Sequences |
1017 | // |
1018 | // This is a variable size field using between 1 and 3 bytes. Let's call its |
1019 | // first byte byte0." |
1020 | u8 header = IO_read_bits(in, 8); |
f535537f |
1021 | if (header < 128) { |
648db22b |
1022 | // "Number_of_Sequences = byte0 . Uses 1 byte." |
1023 | num_sequences = header; |
1024 | } else if (header < 255) { |
1025 | // "Number_of_Sequences = ((byte0-128) << 8) + byte1 . Uses 2 bytes." |
1026 | num_sequences = ((header - 128) << 8) + IO_read_bits(in, 8); |
1027 | } else { |
1028 | // "Number_of_Sequences = byte1 + (byte2<<8) + 0x7F00 . Uses 3 bytes." |
1029 | num_sequences = IO_read_bits(in, 16) + 0x7F00; |
1030 | } |
1031 | |
f535537f |
1032 | if (num_sequences == 0) { |
1033 | // "There are no sequences. The sequence section stops there." |
1034 | *sequences = NULL; |
1035 | return 0; |
1036 | } |
1037 | |
648db22b |
1038 | *sequences = malloc(num_sequences * sizeof(sequence_command_t)); |
1039 | if (!*sequences) { |
1040 | BAD_ALLOC(); |
1041 | } |
1042 | |
1043 | decompress_sequences(ctx, in, *sequences, num_sequences); |
1044 | return num_sequences; |
1045 | } |
1046 | |
1047 | /// Decompress the FSE encoded sequence commands |
1048 | static void decompress_sequences(frame_context_t *const ctx, istream_t *in, |
1049 | sequence_command_t *const sequences, |
1050 | const size_t num_sequences) { |
1051 | // "The Sequences_Section regroup all symbols required to decode commands. |
1052 | // There are 3 symbol types : literals lengths, offsets and match lengths. |
1053 | // They are encoded together, interleaved, in a single bitstream." |
1054 | |
1055 | // "Symbol compression modes |
1056 | // |
1057 | // This is a single byte, defining the compression mode of each symbol |
1058 | // type." |
1059 | // |
1060 | // Bit number : Field name |
1061 | // 7-6 : Literals_Lengths_Mode |
1062 | // 5-4 : Offsets_Mode |
1063 | // 3-2 : Match_Lengths_Mode |
1064 | // 1-0 : Reserved |
1065 | u8 compression_modes = IO_read_bits(in, 8); |
1066 | |
1067 | if ((compression_modes & 3) != 0) { |
1068 | // Reserved bits set |
1069 | CORRUPTION(); |
1070 | } |
1071 | |
1072 | // "Following the header, up to 3 distribution tables can be described. When |
1073 | // present, they are in this order : |
1074 | // |
1075 | // Literals lengths |
1076 | // Offsets |
1077 | // Match Lengths" |
1078 | // Update the tables we have stored in the context |
1079 | decode_seq_table(&ctx->ll_dtable, in, seq_literal_length, |
1080 | (compression_modes >> 6) & 3); |
1081 | |
1082 | decode_seq_table(&ctx->of_dtable, in, seq_offset, |
1083 | (compression_modes >> 4) & 3); |
1084 | |
1085 | decode_seq_table(&ctx->ml_dtable, in, seq_match_length, |
1086 | (compression_modes >> 2) & 3); |
1087 | |
1088 | |
1089 | sequence_states_t states; |
1090 | |
1091 | // Initialize the decoding tables |
1092 | { |
1093 | states.ll_table = ctx->ll_dtable; |
1094 | states.of_table = ctx->of_dtable; |
1095 | states.ml_table = ctx->ml_dtable; |
1096 | } |
1097 | |
1098 | const size_t len = IO_istream_len(in); |
1099 | const u8 *const src = IO_get_read_ptr(in, len); |
1100 | |
1101 | // "After writing the last bit containing information, the compressor writes |
1102 | // a single 1-bit and then fills the byte with 0-7 0 bits of padding." |
1103 | const int padding = 8 - highest_set_bit(src[len - 1]); |
1104 | // The offset starts at the end because FSE streams are read backwards |
1105 | i64 bit_offset = (i64)(len * 8 - (size_t)padding); |
1106 | |
1107 | // "The bitstream starts with initial state values, each using the required |
1108 | // number of bits in their respective accuracy, decoded previously from |
1109 | // their normalized distribution. |
1110 | // |
1111 | // It starts by Literals_Length_State, followed by Offset_State, and finally |
1112 | // Match_Length_State." |
1113 | FSE_init_state(&states.ll_table, &states.ll_state, src, &bit_offset); |
1114 | FSE_init_state(&states.of_table, &states.of_state, src, &bit_offset); |
1115 | FSE_init_state(&states.ml_table, &states.ml_state, src, &bit_offset); |
1116 | |
1117 | for (size_t i = 0; i < num_sequences; i++) { |
1118 | // Decode sequences one by one |
f535537f |
1119 | sequences[i] = decode_sequence(&states, src, &bit_offset, i==num_sequences-1); |
648db22b |
1120 | } |
1121 | |
1122 | if (bit_offset != 0) { |
1123 | CORRUPTION(); |
1124 | } |
1125 | } |
1126 | |
1127 | // Decode a single sequence and update the state |
1128 | static sequence_command_t decode_sequence(sequence_states_t *const states, |
1129 | const u8 *const src, |
f535537f |
1130 | i64 *const offset, |
1131 | int lastSequence) { |
648db22b |
1132 | // "Each symbol is a code in its own context, which specifies Baseline and |
1133 | // Number_of_Bits to add. Codes are FSE compressed, and interleaved with raw |
1134 | // additional bits in the same bitstream." |
1135 | |
1136 | // Decode symbols, but don't update states |
1137 | const u8 of_code = FSE_peek_symbol(&states->of_table, states->of_state); |
1138 | const u8 ll_code = FSE_peek_symbol(&states->ll_table, states->ll_state); |
1139 | const u8 ml_code = FSE_peek_symbol(&states->ml_table, states->ml_state); |
1140 | |
1141 | // Offset doesn't need a max value as it's not decoded using a table |
1142 | if (ll_code > SEQ_MAX_CODES[seq_literal_length] || |
1143 | ml_code > SEQ_MAX_CODES[seq_match_length]) { |
1144 | CORRUPTION(); |
1145 | } |
1146 | |
1147 | // Read the interleaved bits |
1148 | sequence_command_t seq; |
1149 | // "Decoding starts by reading the Number_of_Bits required to decode Offset. |
1150 | // It then does the same for Match_Length, and then for Literals_Length." |
1151 | seq.offset = ((u32)1 << of_code) + STREAM_read_bits(src, of_code, offset); |
1152 | |
1153 | seq.match_length = |
1154 | SEQ_MATCH_LENGTH_BASELINES[ml_code] + |
1155 | STREAM_read_bits(src, SEQ_MATCH_LENGTH_EXTRA_BITS[ml_code], offset); |
1156 | |
1157 | seq.literal_length = |
1158 | SEQ_LITERAL_LENGTH_BASELINES[ll_code] + |
1159 | STREAM_read_bits(src, SEQ_LITERAL_LENGTH_EXTRA_BITS[ll_code], offset); |
1160 | |
1161 | // "If it is not the last sequence in the block, the next operation is to |
1162 | // update states. Using the rules pre-calculated in the decoding tables, |
1163 | // Literals_Length_State is updated, followed by Match_Length_State, and |
1164 | // then Offset_State." |
1165 | // If the stream is complete don't read bits to update state |
f535537f |
1166 | if (!lastSequence) { |
648db22b |
1167 | FSE_update_state(&states->ll_table, &states->ll_state, src, offset); |
1168 | FSE_update_state(&states->ml_table, &states->ml_state, src, offset); |
1169 | FSE_update_state(&states->of_table, &states->of_state, src, offset); |
1170 | } |
1171 | |
1172 | return seq; |
1173 | } |
1174 | |
1175 | /// Given a sequence part and table mode, decode the FSE distribution |
1176 | /// Errors if the mode is `seq_repeat` without a pre-existing table in `table` |
1177 | static void decode_seq_table(FSE_dtable *const table, istream_t *const in, |
1178 | const seq_part_t type, const seq_mode_t mode) { |
1179 | // Constant arrays indexed by seq_part_t |
1180 | const i16 *const default_distributions[] = {SEQ_LITERAL_LENGTH_DEFAULT_DIST, |
1181 | SEQ_OFFSET_DEFAULT_DIST, |
1182 | SEQ_MATCH_LENGTH_DEFAULT_DIST}; |
1183 | const size_t default_distribution_lengths[] = {36, 29, 53}; |
1184 | const size_t default_distribution_accuracies[] = {6, 5, 6}; |
1185 | |
1186 | const size_t max_accuracies[] = {9, 8, 9}; |
1187 | |
1188 | if (mode != seq_repeat) { |
1189 | // Free old one before overwriting |
1190 | FSE_free_dtable(table); |
1191 | } |
1192 | |
1193 | switch (mode) { |
1194 | case seq_predefined: { |
1195 | // "Predefined_Mode : uses a predefined distribution table." |
1196 | const i16 *distribution = default_distributions[type]; |
1197 | const size_t symbs = default_distribution_lengths[type]; |
1198 | const size_t accuracy_log = default_distribution_accuracies[type]; |
1199 | |
1200 | FSE_init_dtable(table, distribution, symbs, accuracy_log); |
1201 | break; |
1202 | } |
1203 | case seq_rle: { |
1204 | // "RLE_Mode : it's a single code, repeated Number_of_Sequences times." |
1205 | const u8 symb = IO_get_read_ptr(in, 1)[0]; |
1206 | FSE_init_dtable_rle(table, symb); |
1207 | break; |
1208 | } |
1209 | case seq_fse: { |
1210 | // "FSE_Compressed_Mode : standard FSE compression. A distribution table |
1211 | // will be present " |
1212 | FSE_decode_header(table, in, max_accuracies[type]); |
1213 | break; |
1214 | } |
1215 | case seq_repeat: |
f535537f |
1216 | // "Repeat_Mode : reuse distribution table from previous compressed |
648db22b |
1217 | // block." |
1218 | // Nothing to do here, table will be unchanged |
1219 | if (!table->symbols) { |
1220 | // This mode is invalid if we don't already have a table |
1221 | CORRUPTION(); |
1222 | } |
1223 | break; |
1224 | default: |
1225 | // Impossible, as mode is from 0-3 |
1226 | IMPOSSIBLE(); |
1227 | break; |
1228 | } |
1229 | |
1230 | } |
1231 | /******* END SEQUENCE DECODING ************************************************/ |
1232 | |
1233 | /******* SEQUENCE EXECUTION ***************************************************/ |
1234 | static void execute_sequences(frame_context_t *const ctx, ostream_t *const out, |
1235 | const u8 *const literals, |
1236 | const size_t literals_len, |
1237 | const sequence_command_t *const sequences, |
1238 | const size_t num_sequences) { |
1239 | istream_t litstream = IO_make_istream(literals, literals_len); |
1240 | |
1241 | u64 *const offset_hist = ctx->previous_offsets; |
1242 | size_t total_output = ctx->current_total_output; |
1243 | |
1244 | for (size_t i = 0; i < num_sequences; i++) { |
1245 | const sequence_command_t seq = sequences[i]; |
1246 | { |
1247 | const u32 literals_size = copy_literals(seq.literal_length, &litstream, out); |
1248 | total_output += literals_size; |
1249 | } |
1250 | |
1251 | size_t const offset = compute_offset(seq, offset_hist); |
1252 | |
1253 | size_t const match_length = seq.match_length; |
1254 | |
1255 | execute_match_copy(ctx, offset, match_length, total_output, out); |
1256 | |
1257 | total_output += match_length; |
1258 | } |
1259 | |
1260 | // Copy any leftover literals |
1261 | { |
1262 | size_t len = IO_istream_len(&litstream); |
1263 | copy_literals(len, &litstream, out); |
1264 | total_output += len; |
1265 | } |
1266 | |
1267 | ctx->current_total_output = total_output; |
1268 | } |
1269 | |
1270 | static u32 copy_literals(const size_t literal_length, istream_t *litstream, |
1271 | ostream_t *const out) { |
1272 | // If the sequence asks for more literals than are left, the |
1273 | // sequence must be corrupted |
1274 | if (literal_length > IO_istream_len(litstream)) { |
1275 | CORRUPTION(); |
1276 | } |
1277 | |
1278 | u8 *const write_ptr = IO_get_write_ptr(out, literal_length); |
1279 | const u8 *const read_ptr = |
1280 | IO_get_read_ptr(litstream, literal_length); |
1281 | // Copy literals to output |
1282 | memcpy(write_ptr, read_ptr, literal_length); |
1283 | |
1284 | return literal_length; |
1285 | } |
1286 | |
1287 | static size_t compute_offset(sequence_command_t seq, u64 *const offset_hist) { |
1288 | size_t offset; |
1289 | // Offsets are special, we need to handle the repeat offsets |
1290 | if (seq.offset <= 3) { |
1291 | // "The first 3 values define a repeated offset and we will call |
1292 | // them Repeated_Offset1, Repeated_Offset2, and Repeated_Offset3. |
1293 | // They are sorted in recency order, with Repeated_Offset1 meaning |
1294 | // 'most recent one'". |
1295 | |
1296 | // Use 0 indexing for the array |
1297 | u32 idx = seq.offset - 1; |
1298 | if (seq.literal_length == 0) { |
1299 | // "There is an exception though, when current sequence's |
1300 | // literals length is 0. In this case, repeated offsets are |
1301 | // shifted by one, so Repeated_Offset1 becomes Repeated_Offset2, |
1302 | // Repeated_Offset2 becomes Repeated_Offset3, and |
1303 | // Repeated_Offset3 becomes Repeated_Offset1 - 1_byte." |
1304 | idx++; |
1305 | } |
1306 | |
1307 | if (idx == 0) { |
1308 | offset = offset_hist[0]; |
1309 | } else { |
1310 | // If idx == 3 then literal length was 0 and the offset was 3, |
1311 | // as per the exception listed above |
1312 | offset = idx < 3 ? offset_hist[idx] : offset_hist[0] - 1; |
1313 | |
1314 | // If idx == 1 we don't need to modify offset_hist[2], since |
1315 | // we're using the second-most recent code |
1316 | if (idx > 1) { |
1317 | offset_hist[2] = offset_hist[1]; |
1318 | } |
1319 | offset_hist[1] = offset_hist[0]; |
1320 | offset_hist[0] = offset; |
1321 | } |
1322 | } else { |
1323 | // When it's not a repeat offset: |
1324 | // "if (Offset_Value > 3) offset = Offset_Value - 3;" |
1325 | offset = seq.offset - 3; |
1326 | |
1327 | // Shift back history |
1328 | offset_hist[2] = offset_hist[1]; |
1329 | offset_hist[1] = offset_hist[0]; |
1330 | offset_hist[0] = offset; |
1331 | } |
1332 | return offset; |
1333 | } |
1334 | |
1335 | static void execute_match_copy(frame_context_t *const ctx, size_t offset, |
1336 | size_t match_length, size_t total_output, |
1337 | ostream_t *const out) { |
1338 | u8 *write_ptr = IO_get_write_ptr(out, match_length); |
1339 | if (total_output <= ctx->header.window_size) { |
1340 | // In this case offset might go back into the dictionary |
1341 | if (offset > total_output + ctx->dict_content_len) { |
1342 | // The offset goes beyond even the dictionary |
1343 | CORRUPTION(); |
1344 | } |
1345 | |
1346 | if (offset > total_output) { |
1347 | // "The rest of the dictionary is its content. The content act |
1348 | // as a "past" in front of data to compress or decompress, so it |
1349 | // can be referenced in sequence commands." |
1350 | const size_t dict_copy = |
1351 | MIN(offset - total_output, match_length); |
1352 | const size_t dict_offset = |
1353 | ctx->dict_content_len - (offset - total_output); |
1354 | |
1355 | memcpy(write_ptr, ctx->dict_content + dict_offset, dict_copy); |
1356 | write_ptr += dict_copy; |
1357 | match_length -= dict_copy; |
1358 | } |
1359 | } else if (offset > ctx->header.window_size) { |
1360 | CORRUPTION(); |
1361 | } |
1362 | |
1363 | // We must copy byte by byte because the match length might be larger |
1364 | // than the offset |
1365 | // ex: if the output so far was "abc", a command with offset=3 and |
1366 | // match_length=6 would produce "abcabcabc" as the new output |
1367 | for (size_t j = 0; j < match_length; j++) { |
1368 | *write_ptr = *(write_ptr - offset); |
1369 | write_ptr++; |
1370 | } |
1371 | } |
1372 | /******* END SEQUENCE EXECUTION ***********************************************/ |
1373 | |
1374 | /******* OUTPUT SIZE COUNTING *************************************************/ |
1375 | /// Get the decompressed size of an input stream so memory can be allocated in |
1376 | /// advance. |
1377 | /// This implementation assumes `src` points to a single ZSTD-compressed frame |
1378 | size_t ZSTD_get_decompressed_size(const void *src, const size_t src_len) { |
1379 | istream_t in = IO_make_istream(src, src_len); |
1380 | |
1381 | // get decompressed size from ZSTD frame header |
1382 | { |
1383 | const u32 magic_number = (u32)IO_read_bits(&in, 32); |
1384 | |
1385 | if (magic_number == ZSTD_MAGIC_NUMBER) { |
1386 | // ZSTD frame |
1387 | frame_header_t header; |
1388 | parse_frame_header(&header, &in); |
1389 | |
1390 | if (header.frame_content_size == 0 && !header.single_segment_flag) { |
1391 | // Content size not provided, we can't tell |
1392 | return (size_t)-1; |
1393 | } |
1394 | |
1395 | return header.frame_content_size; |
1396 | } else { |
1397 | // not a real frame or skippable frame |
1398 | ERROR("ZSTD frame magic number did not match"); |
1399 | } |
1400 | } |
1401 | } |
1402 | /******* END OUTPUT SIZE COUNTING *********************************************/ |
1403 | |
1404 | /******* DICTIONARY PARSING ***************************************************/ |
f535537f |
1405 | dictionary_t* create_dictionary(void) { |
648db22b |
1406 | dictionary_t* const dict = calloc(1, sizeof(dictionary_t)); |
1407 | if (!dict) { |
1408 | BAD_ALLOC(); |
1409 | } |
1410 | return dict; |
1411 | } |
1412 | |
1413 | /// Free an allocated dictionary |
1414 | void free_dictionary(dictionary_t *const dict) { |
1415 | HUF_free_dtable(&dict->literals_dtable); |
1416 | FSE_free_dtable(&dict->ll_dtable); |
1417 | FSE_free_dtable(&dict->of_dtable); |
1418 | FSE_free_dtable(&dict->ml_dtable); |
1419 | |
1420 | free(dict->content); |
1421 | |
1422 | memset(dict, 0, sizeof(dictionary_t)); |
1423 | |
1424 | free(dict); |
1425 | } |
1426 | |
1427 | |
1428 | #if !defined(ZDEC_NO_DICTIONARY) |
1429 | #define DICT_SIZE_ERROR() ERROR("Dictionary size cannot be less than 8 bytes") |
1430 | #define NULL_SRC() ERROR("Tried to create dictionary with pointer to null src"); |
1431 | |
1432 | static void init_dictionary_content(dictionary_t *const dict, |
1433 | istream_t *const in); |
1434 | |
1435 | void parse_dictionary(dictionary_t *const dict, const void *src, |
1436 | size_t src_len) { |
1437 | const u8 *byte_src = (const u8 *)src; |
1438 | memset(dict, 0, sizeof(dictionary_t)); |
1439 | if (src == NULL) { /* cannot initialize dictionary with null src */ |
1440 | NULL_SRC(); |
1441 | } |
1442 | if (src_len < 8) { |
1443 | DICT_SIZE_ERROR(); |
1444 | } |
1445 | |
1446 | istream_t in = IO_make_istream(byte_src, src_len); |
1447 | |
1448 | const u32 magic_number = IO_read_bits(&in, 32); |
1449 | if (magic_number != 0xEC30A437) { |
1450 | // raw content dict |
1451 | IO_rewind_bits(&in, 32); |
1452 | init_dictionary_content(dict, &in); |
1453 | return; |
1454 | } |
1455 | |
1456 | dict->dictionary_id = IO_read_bits(&in, 32); |
1457 | |
1458 | // "Entropy_Tables : following the same format as the tables in compressed |
1459 | // blocks. They are stored in following order : Huffman tables for literals, |
1460 | // FSE table for offsets, FSE table for match lengths, and FSE table for |
1461 | // literals lengths. It's finally followed by 3 offset values, populating |
1462 | // recent offsets (instead of using {1,4,8}), stored in order, 4-bytes |
1463 | // little-endian each, for a total of 12 bytes. Each recent offset must have |
1464 | // a value < dictionary size." |
1465 | decode_huf_table(&dict->literals_dtable, &in); |
1466 | decode_seq_table(&dict->of_dtable, &in, seq_offset, seq_fse); |
1467 | decode_seq_table(&dict->ml_dtable, &in, seq_match_length, seq_fse); |
1468 | decode_seq_table(&dict->ll_dtable, &in, seq_literal_length, seq_fse); |
1469 | |
1470 | // Read in the previous offset history |
1471 | dict->previous_offsets[0] = IO_read_bits(&in, 32); |
1472 | dict->previous_offsets[1] = IO_read_bits(&in, 32); |
1473 | dict->previous_offsets[2] = IO_read_bits(&in, 32); |
1474 | |
1475 | // Ensure the provided offsets aren't too large |
1476 | // "Each recent offset must have a value < dictionary size." |
1477 | for (int i = 0; i < 3; i++) { |
1478 | if (dict->previous_offsets[i] > src_len) { |
1479 | ERROR("Dictionary corrupted"); |
1480 | } |
1481 | } |
1482 | |
1483 | // "Content : The rest of the dictionary is its content. The content act as |
1484 | // a "past" in front of data to compress or decompress, so it can be |
1485 | // referenced in sequence commands." |
1486 | init_dictionary_content(dict, &in); |
1487 | } |
1488 | |
1489 | static void init_dictionary_content(dictionary_t *const dict, |
1490 | istream_t *const in) { |
1491 | // Copy in the content |
1492 | dict->content_size = IO_istream_len(in); |
1493 | dict->content = malloc(dict->content_size); |
1494 | if (!dict->content) { |
1495 | BAD_ALLOC(); |
1496 | } |
1497 | |
1498 | const u8 *const content = IO_get_read_ptr(in, dict->content_size); |
1499 | |
1500 | memcpy(dict->content, content, dict->content_size); |
1501 | } |
1502 | |
1503 | static void HUF_copy_dtable(HUF_dtable *const dst, |
1504 | const HUF_dtable *const src) { |
1505 | if (src->max_bits == 0) { |
1506 | memset(dst, 0, sizeof(HUF_dtable)); |
1507 | return; |
1508 | } |
1509 | |
1510 | const size_t size = (size_t)1 << src->max_bits; |
1511 | dst->max_bits = src->max_bits; |
1512 | |
1513 | dst->symbols = malloc(size); |
1514 | dst->num_bits = malloc(size); |
1515 | if (!dst->symbols || !dst->num_bits) { |
1516 | BAD_ALLOC(); |
1517 | } |
1518 | |
1519 | memcpy(dst->symbols, src->symbols, size); |
1520 | memcpy(dst->num_bits, src->num_bits, size); |
1521 | } |
1522 | |
1523 | static void FSE_copy_dtable(FSE_dtable *const dst, const FSE_dtable *const src) { |
1524 | if (src->accuracy_log == 0) { |
1525 | memset(dst, 0, sizeof(FSE_dtable)); |
1526 | return; |
1527 | } |
1528 | |
1529 | size_t size = (size_t)1 << src->accuracy_log; |
1530 | dst->accuracy_log = src->accuracy_log; |
1531 | |
1532 | dst->symbols = malloc(size); |
1533 | dst->num_bits = malloc(size); |
1534 | dst->new_state_base = malloc(size * sizeof(u16)); |
1535 | if (!dst->symbols || !dst->num_bits || !dst->new_state_base) { |
1536 | BAD_ALLOC(); |
1537 | } |
1538 | |
1539 | memcpy(dst->symbols, src->symbols, size); |
1540 | memcpy(dst->num_bits, src->num_bits, size); |
1541 | memcpy(dst->new_state_base, src->new_state_base, size * sizeof(u16)); |
1542 | } |
1543 | |
1544 | /// A dictionary acts as initializing values for the frame context before |
1545 | /// decompression, so we implement it by applying it's predetermined |
1546 | /// tables and content to the context before beginning decompression |
1547 | static void frame_context_apply_dict(frame_context_t *const ctx, |
1548 | const dictionary_t *const dict) { |
1549 | // If the content pointer is NULL then it must be an empty dict |
1550 | if (!dict || !dict->content) |
1551 | return; |
1552 | |
1553 | // If the requested dictionary_id is non-zero, the correct dictionary must |
1554 | // be present |
1555 | if (ctx->header.dictionary_id != 0 && |
1556 | ctx->header.dictionary_id != dict->dictionary_id) { |
1557 | ERROR("Wrong dictionary provided"); |
1558 | } |
1559 | |
1560 | // Copy the dict content to the context for references during sequence |
1561 | // execution |
1562 | ctx->dict_content = dict->content; |
1563 | ctx->dict_content_len = dict->content_size; |
1564 | |
1565 | // If it's a formatted dict copy the precomputed tables in so they can |
1566 | // be used in the table repeat modes |
1567 | if (dict->dictionary_id != 0) { |
1568 | // Deep copy the entropy tables so they can be freed independently of |
1569 | // the dictionary struct |
1570 | HUF_copy_dtable(&ctx->literals_dtable, &dict->literals_dtable); |
1571 | FSE_copy_dtable(&ctx->ll_dtable, &dict->ll_dtable); |
1572 | FSE_copy_dtable(&ctx->of_dtable, &dict->of_dtable); |
1573 | FSE_copy_dtable(&ctx->ml_dtable, &dict->ml_dtable); |
1574 | |
1575 | // Copy the repeated offsets |
1576 | memcpy(ctx->previous_offsets, dict->previous_offsets, |
1577 | sizeof(ctx->previous_offsets)); |
1578 | } |
1579 | } |
1580 | |
1581 | #else // ZDEC_NO_DICTIONARY is defined |
1582 | |
1583 | static void frame_context_apply_dict(frame_context_t *const ctx, |
1584 | const dictionary_t *const dict) { |
1585 | (void)ctx; |
1586 | if (dict && dict->content) ERROR("dictionary not supported"); |
1587 | } |
1588 | |
1589 | #endif |
1590 | /******* END DICTIONARY PARSING ***********************************************/ |
1591 | |
1592 | /******* IO STREAM OPERATIONS *************************************************/ |
1593 | |
1594 | /// Reads `num` bits from a bitstream, and updates the internal offset |
1595 | static inline u64 IO_read_bits(istream_t *const in, const int num_bits) { |
1596 | if (num_bits > 64 || num_bits <= 0) { |
1597 | ERROR("Attempt to read an invalid number of bits"); |
1598 | } |
1599 | |
1600 | const size_t bytes = (num_bits + in->bit_offset + 7) / 8; |
1601 | const size_t full_bytes = (num_bits + in->bit_offset) / 8; |
1602 | if (bytes > in->len) { |
1603 | INP_SIZE(); |
1604 | } |
1605 | |
1606 | const u64 result = read_bits_LE(in->ptr, num_bits, in->bit_offset); |
1607 | |
1608 | in->bit_offset = (num_bits + in->bit_offset) % 8; |
1609 | in->ptr += full_bytes; |
1610 | in->len -= full_bytes; |
1611 | |
1612 | return result; |
1613 | } |
1614 | |
1615 | /// If a non-zero number of bits have been read from the current byte, advance |
1616 | /// the offset to the next byte |
1617 | static inline void IO_rewind_bits(istream_t *const in, int num_bits) { |
1618 | if (num_bits < 0) { |
1619 | ERROR("Attempting to rewind stream by a negative number of bits"); |
1620 | } |
1621 | |
1622 | // move the offset back by `num_bits` bits |
1623 | const int new_offset = in->bit_offset - num_bits; |
1624 | // determine the number of whole bytes we have to rewind, rounding up to an |
1625 | // integer number (e.g. if `new_offset == -5`, `bytes == 1`) |
1626 | const i64 bytes = -(new_offset - 7) / 8; |
1627 | |
1628 | in->ptr -= bytes; |
1629 | in->len += bytes; |
1630 | // make sure the resulting `bit_offset` is positive, as mod in C does not |
1631 | // convert numbers from negative to positive (e.g. -22 % 8 == -6) |
1632 | in->bit_offset = ((new_offset % 8) + 8) % 8; |
1633 | } |
1634 | |
1635 | /// If the remaining bits in a byte will be unused, advance to the end of the |
1636 | /// byte |
1637 | static inline void IO_align_stream(istream_t *const in) { |
1638 | if (in->bit_offset != 0) { |
1639 | if (in->len == 0) { |
1640 | INP_SIZE(); |
1641 | } |
1642 | in->ptr++; |
1643 | in->len--; |
1644 | in->bit_offset = 0; |
1645 | } |
1646 | } |
1647 | |
1648 | /// Write the given byte into the output stream |
1649 | static inline void IO_write_byte(ostream_t *const out, u8 symb) { |
1650 | if (out->len == 0) { |
1651 | OUT_SIZE(); |
1652 | } |
1653 | |
1654 | out->ptr[0] = symb; |
1655 | out->ptr++; |
1656 | out->len--; |
1657 | } |
1658 | |
1659 | /// Returns the number of bytes left to be read in this stream. The stream must |
1660 | /// be byte aligned. |
1661 | static inline size_t IO_istream_len(const istream_t *const in) { |
1662 | return in->len; |
1663 | } |
1664 | |
1665 | /// Returns a pointer where `len` bytes can be read, and advances the internal |
1666 | /// state. The stream must be byte aligned. |
1667 | static inline const u8 *IO_get_read_ptr(istream_t *const in, size_t len) { |
1668 | if (len > in->len) { |
1669 | INP_SIZE(); |
1670 | } |
1671 | if (in->bit_offset != 0) { |
1672 | ERROR("Attempting to operate on a non-byte aligned stream"); |
1673 | } |
1674 | const u8 *const ptr = in->ptr; |
1675 | in->ptr += len; |
1676 | in->len -= len; |
1677 | |
1678 | return ptr; |
1679 | } |
1680 | /// Returns a pointer to write `len` bytes to, and advances the internal state |
1681 | static inline u8 *IO_get_write_ptr(ostream_t *const out, size_t len) { |
1682 | if (len > out->len) { |
1683 | OUT_SIZE(); |
1684 | } |
1685 | u8 *const ptr = out->ptr; |
1686 | out->ptr += len; |
1687 | out->len -= len; |
1688 | |
1689 | return ptr; |
1690 | } |
1691 | |
1692 | /// Advance the inner state by `len` bytes |
1693 | static inline void IO_advance_input(istream_t *const in, size_t len) { |
1694 | if (len > in->len) { |
1695 | INP_SIZE(); |
1696 | } |
1697 | if (in->bit_offset != 0) { |
1698 | ERROR("Attempting to operate on a non-byte aligned stream"); |
1699 | } |
1700 | |
1701 | in->ptr += len; |
1702 | in->len -= len; |
1703 | } |
1704 | |
1705 | /// Returns an `ostream_t` constructed from the given pointer and length |
1706 | static inline ostream_t IO_make_ostream(u8 *out, size_t len) { |
1707 | return (ostream_t) { out, len }; |
1708 | } |
1709 | |
1710 | /// Returns an `istream_t` constructed from the given pointer and length |
1711 | static inline istream_t IO_make_istream(const u8 *in, size_t len) { |
1712 | return (istream_t) { in, len, 0 }; |
1713 | } |
1714 | |
1715 | /// Returns an `istream_t` with the same base as `in`, and length `len` |
1716 | /// Then, advance `in` to account for the consumed bytes |
1717 | /// `in` must be byte aligned |
1718 | static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len) { |
1719 | // Consume `len` bytes of the parent stream |
1720 | const u8 *const ptr = IO_get_read_ptr(in, len); |
1721 | |
1722 | // Make a substream using the pointer to those `len` bytes |
1723 | return IO_make_istream(ptr, len); |
1724 | } |
1725 | /******* END IO STREAM OPERATIONS *********************************************/ |
1726 | |
1727 | /******* BITSTREAM OPERATIONS *************************************************/ |
1728 | /// Read `num` bits (up to 64) from `src + offset`, where `offset` is in bits |
1729 | static inline u64 read_bits_LE(const u8 *src, const int num_bits, |
1730 | const size_t offset) { |
1731 | if (num_bits > 64) { |
1732 | ERROR("Attempt to read an invalid number of bits"); |
1733 | } |
1734 | |
1735 | // Skip over bytes that aren't in range |
1736 | src += offset / 8; |
1737 | size_t bit_offset = offset % 8; |
1738 | u64 res = 0; |
1739 | |
1740 | int shift = 0; |
1741 | int left = num_bits; |
1742 | while (left > 0) { |
1743 | u64 mask = left >= 8 ? 0xff : (((u64)1 << left) - 1); |
1744 | // Read the next byte, shift it to account for the offset, and then mask |
1745 | // out the top part if we don't need all the bits |
1746 | res += (((u64)*src++ >> bit_offset) & mask) << shift; |
1747 | shift += 8 - bit_offset; |
1748 | left -= 8 - bit_offset; |
1749 | bit_offset = 0; |
1750 | } |
1751 | |
1752 | return res; |
1753 | } |
1754 | |
1755 | /// Read bits from the end of a HUF or FSE bitstream. `offset` is in bits, so |
1756 | /// it updates `offset` to `offset - bits`, and then reads `bits` bits from |
1757 | /// `src + offset`. If the offset becomes negative, the extra bits at the |
1758 | /// bottom are filled in with `0` bits instead of reading from before `src`. |
1759 | static inline u64 STREAM_read_bits(const u8 *const src, const int bits, |
1760 | i64 *const offset) { |
1761 | *offset = *offset - bits; |
1762 | size_t actual_off = *offset; |
1763 | size_t actual_bits = bits; |
1764 | // Don't actually read bits from before the start of src, so if `*offset < |
1765 | // 0` fix actual_off and actual_bits to reflect the quantity to read |
1766 | if (*offset < 0) { |
1767 | actual_bits += *offset; |
1768 | actual_off = 0; |
1769 | } |
1770 | u64 res = read_bits_LE(src, actual_bits, actual_off); |
1771 | |
1772 | if (*offset < 0) { |
1773 | // Fill in the bottom "overflowed" bits with 0's |
1774 | res = -*offset >= 64 ? 0 : (res << -*offset); |
1775 | } |
1776 | return res; |
1777 | } |
1778 | /******* END BITSTREAM OPERATIONS *********************************************/ |
1779 | |
1780 | /******* BIT COUNTING OPERATIONS **********************************************/ |
1781 | /// Returns `x`, where `2^x` is the largest power of 2 less than or equal to |
1782 | /// `num`, or `-1` if `num == 0`. |
1783 | static inline int highest_set_bit(const u64 num) { |
1784 | for (int i = 63; i >= 0; i--) { |
1785 | if (((u64)1 << i) <= num) { |
1786 | return i; |
1787 | } |
1788 | } |
1789 | return -1; |
1790 | } |
1791 | /******* END BIT COUNTING OPERATIONS ******************************************/ |
1792 | |
1793 | /******* HUFFMAN PRIMITIVES ***************************************************/ |
1794 | static inline u8 HUF_decode_symbol(const HUF_dtable *const dtable, |
1795 | u16 *const state, const u8 *const src, |
1796 | i64 *const offset) { |
1797 | // Look up the symbol and number of bits to read |
1798 | const u8 symb = dtable->symbols[*state]; |
1799 | const u8 bits = dtable->num_bits[*state]; |
1800 | const u16 rest = STREAM_read_bits(src, bits, offset); |
1801 | // Shift `bits` bits out of the state, keeping the low order bits that |
1802 | // weren't necessary to determine this symbol. Then add in the new bits |
1803 | // read from the stream. |
1804 | *state = ((*state << bits) + rest) & (((u16)1 << dtable->max_bits) - 1); |
1805 | |
1806 | return symb; |
1807 | } |
1808 | |
1809 | static inline void HUF_init_state(const HUF_dtable *const dtable, |
1810 | u16 *const state, const u8 *const src, |
1811 | i64 *const offset) { |
1812 | // Read in a full `dtable->max_bits` bits to initialize the state |
1813 | const u8 bits = dtable->max_bits; |
1814 | *state = STREAM_read_bits(src, bits, offset); |
1815 | } |
1816 | |
1817 | static size_t HUF_decompress_1stream(const HUF_dtable *const dtable, |
1818 | ostream_t *const out, |
1819 | istream_t *const in) { |
1820 | const size_t len = IO_istream_len(in); |
1821 | if (len == 0) { |
1822 | INP_SIZE(); |
1823 | } |
1824 | const u8 *const src = IO_get_read_ptr(in, len); |
1825 | |
1826 | // "Each bitstream must be read backward, that is starting from the end down |
1827 | // to the beginning. Therefore it's necessary to know the size of each |
1828 | // bitstream. |
1829 | // |
1830 | // It's also necessary to know exactly which bit is the latest. This is |
1831 | // detected by a final bit flag : the highest bit of latest byte is a |
1832 | // final-bit-flag. Consequently, a last byte of 0 is not possible. And the |
1833 | // final-bit-flag itself is not part of the useful bitstream. Hence, the |
1834 | // last byte contains between 0 and 7 useful bits." |
1835 | const int padding = 8 - highest_set_bit(src[len - 1]); |
1836 | |
1837 | // Offset starts at the end because HUF streams are read backwards |
1838 | i64 bit_offset = len * 8 - padding; |
1839 | u16 state; |
1840 | |
1841 | HUF_init_state(dtable, &state, src, &bit_offset); |
1842 | |
1843 | size_t symbols_written = 0; |
1844 | while (bit_offset > -dtable->max_bits) { |
1845 | // Iterate over the stream, decoding one symbol at a time |
1846 | IO_write_byte(out, HUF_decode_symbol(dtable, &state, src, &bit_offset)); |
1847 | symbols_written++; |
1848 | } |
1849 | // "The process continues up to reading the required number of symbols per |
1850 | // stream. If a bitstream is not entirely and exactly consumed, hence |
1851 | // reaching exactly its beginning position with all bits consumed, the |
1852 | // decoding process is considered faulty." |
1853 | |
1854 | // When all symbols have been decoded, the final state value shouldn't have |
1855 | // any data from the stream, so it should have "read" dtable->max_bits from |
1856 | // before the start of `src` |
1857 | // Therefore `offset`, the edge to start reading new bits at, should be |
1858 | // dtable->max_bits before the start of the stream |
1859 | if (bit_offset != -dtable->max_bits) { |
1860 | CORRUPTION(); |
1861 | } |
1862 | |
1863 | return symbols_written; |
1864 | } |
1865 | |
1866 | static size_t HUF_decompress_4stream(const HUF_dtable *const dtable, |
1867 | ostream_t *const out, istream_t *const in) { |
1868 | // "Compressed size is provided explicitly : in the 4-streams variant, |
1869 | // bitstreams are preceded by 3 unsigned little-endian 16-bits values. Each |
1870 | // value represents the compressed size of one stream, in order. The last |
1871 | // stream size is deducted from total compressed size and from previously |
1872 | // decoded stream sizes" |
1873 | const size_t csize1 = IO_read_bits(in, 16); |
1874 | const size_t csize2 = IO_read_bits(in, 16); |
1875 | const size_t csize3 = IO_read_bits(in, 16); |
1876 | |
1877 | istream_t in1 = IO_make_sub_istream(in, csize1); |
1878 | istream_t in2 = IO_make_sub_istream(in, csize2); |
1879 | istream_t in3 = IO_make_sub_istream(in, csize3); |
1880 | istream_t in4 = IO_make_sub_istream(in, IO_istream_len(in)); |
1881 | |
1882 | size_t total_output = 0; |
1883 | // Decode each stream independently for simplicity |
1884 | // If we wanted to we could decode all 4 at the same time for speed, |
1885 | // utilizing more execution units |
1886 | total_output += HUF_decompress_1stream(dtable, out, &in1); |
1887 | total_output += HUF_decompress_1stream(dtable, out, &in2); |
1888 | total_output += HUF_decompress_1stream(dtable, out, &in3); |
1889 | total_output += HUF_decompress_1stream(dtable, out, &in4); |
1890 | |
1891 | return total_output; |
1892 | } |
1893 | |
1894 | /// Initializes a Huffman table using canonical Huffman codes |
1895 | /// For more explanation on canonical Huffman codes see |
1896 | /// https://www.cs.scranton.edu/~mccloske/courses/cmps340/huff_canonical_dec2015.html |
1897 | /// Codes within a level are allocated in symbol order (i.e. smaller symbols get |
1898 | /// earlier codes) |
1899 | static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, |
1900 | const int num_symbs) { |
1901 | memset(table, 0, sizeof(HUF_dtable)); |
1902 | if (num_symbs > HUF_MAX_SYMBS) { |
1903 | ERROR("Too many symbols for Huffman"); |
1904 | } |
1905 | |
1906 | u8 max_bits = 0; |
1907 | u16 rank_count[HUF_MAX_BITS + 1]; |
1908 | memset(rank_count, 0, sizeof(rank_count)); |
1909 | |
1910 | // Count the number of symbols for each number of bits, and determine the |
1911 | // depth of the tree |
1912 | for (int i = 0; i < num_symbs; i++) { |
1913 | if (bits[i] > HUF_MAX_BITS) { |
1914 | ERROR("Huffman table depth too large"); |
1915 | } |
1916 | max_bits = MAX(max_bits, bits[i]); |
1917 | rank_count[bits[i]]++; |
1918 | } |
1919 | |
1920 | const size_t table_size = 1 << max_bits; |
1921 | table->max_bits = max_bits; |
1922 | table->symbols = malloc(table_size); |
1923 | table->num_bits = malloc(table_size); |
1924 | |
1925 | if (!table->symbols || !table->num_bits) { |
1926 | free(table->symbols); |
1927 | free(table->num_bits); |
1928 | BAD_ALLOC(); |
1929 | } |
1930 | |
1931 | // "Symbols are sorted by Weight. Within same Weight, symbols keep natural |
1932 | // order. Symbols with a Weight of zero are removed. Then, starting from |
1933 | // lowest weight, prefix codes are distributed in order." |
1934 | |
1935 | u32 rank_idx[HUF_MAX_BITS + 1]; |
1936 | // Initialize the starting codes for each rank (number of bits) |
1937 | rank_idx[max_bits] = 0; |
1938 | for (int i = max_bits; i >= 1; i--) { |
1939 | rank_idx[i - 1] = rank_idx[i] + rank_count[i] * (1 << (max_bits - i)); |
1940 | // The entire range takes the same number of bits so we can memset it |
1941 | memset(&table->num_bits[rank_idx[i]], i, rank_idx[i - 1] - rank_idx[i]); |
1942 | } |
1943 | |
1944 | if (rank_idx[0] != table_size) { |
1945 | CORRUPTION(); |
1946 | } |
1947 | |
1948 | // Allocate codes and fill in the table |
1949 | for (int i = 0; i < num_symbs; i++) { |
1950 | if (bits[i] != 0) { |
1951 | // Allocate a code for this symbol and set its range in the table |
1952 | const u16 code = rank_idx[bits[i]]; |
1953 | // Since the code doesn't care about the bottom `max_bits - bits[i]` |
1954 | // bits of state, it gets a range that spans all possible values of |
1955 | // the lower bits |
1956 | const u16 len = 1 << (max_bits - bits[i]); |
1957 | memset(&table->symbols[code], i, len); |
1958 | rank_idx[bits[i]] += len; |
1959 | } |
1960 | } |
1961 | } |
1962 | |
1963 | static void HUF_init_dtable_usingweights(HUF_dtable *const table, |
1964 | const u8 *const weights, |
1965 | const int num_symbs) { |
1966 | // +1 because the last weight is not transmitted in the header |
1967 | if (num_symbs + 1 > HUF_MAX_SYMBS) { |
1968 | ERROR("Too many symbols for Huffman"); |
1969 | } |
1970 | |
1971 | u8 bits[HUF_MAX_SYMBS]; |
1972 | |
1973 | u64 weight_sum = 0; |
1974 | for (int i = 0; i < num_symbs; i++) { |
1975 | // Weights are in the same range as bit count |
1976 | if (weights[i] > HUF_MAX_BITS) { |
1977 | CORRUPTION(); |
1978 | } |
1979 | weight_sum += weights[i] > 0 ? (u64)1 << (weights[i] - 1) : 0; |
1980 | } |
1981 | |
1982 | // Find the first power of 2 larger than the sum |
1983 | const int max_bits = highest_set_bit(weight_sum) + 1; |
1984 | const u64 left_over = ((u64)1 << max_bits) - weight_sum; |
1985 | // If the left over isn't a power of 2, the weights are invalid |
1986 | if (left_over & (left_over - 1)) { |
1987 | CORRUPTION(); |
1988 | } |
1989 | |
1990 | // left_over is used to find the last weight as it's not transmitted |
1991 | // by inverting 2^(weight - 1) we can determine the value of last_weight |
1992 | const int last_weight = highest_set_bit(left_over) + 1; |
1993 | |
1994 | for (int i = 0; i < num_symbs; i++) { |
1995 | // "Number_of_Bits = Number_of_Bits ? Max_Number_of_Bits + 1 - Weight : 0" |
1996 | bits[i] = weights[i] > 0 ? (max_bits + 1 - weights[i]) : 0; |
1997 | } |
1998 | bits[num_symbs] = |
1999 | max_bits + 1 - last_weight; // Last weight is always non-zero |
2000 | |
2001 | HUF_init_dtable(table, bits, num_symbs + 1); |
2002 | } |
2003 | |
2004 | static void HUF_free_dtable(HUF_dtable *const dtable) { |
2005 | free(dtable->symbols); |
2006 | free(dtable->num_bits); |
2007 | memset(dtable, 0, sizeof(HUF_dtable)); |
2008 | } |
2009 | /******* END HUFFMAN PRIMITIVES ***********************************************/ |
2010 | |
2011 | /******* FSE PRIMITIVES *******************************************************/ |
2012 | /// For more description of FSE see |
2013 | /// https://github.com/Cyan4973/FiniteStateEntropy/ |
2014 | |
2015 | /// Allow a symbol to be decoded without updating state |
2016 | static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, |
2017 | const u16 state) { |
2018 | return dtable->symbols[state]; |
2019 | } |
2020 | |
2021 | /// Consumes bits from the input and uses the current state to determine the |
2022 | /// next state |
2023 | static inline void FSE_update_state(const FSE_dtable *const dtable, |
2024 | u16 *const state, const u8 *const src, |
2025 | i64 *const offset) { |
2026 | const u8 bits = dtable->num_bits[*state]; |
2027 | const u16 rest = STREAM_read_bits(src, bits, offset); |
2028 | *state = dtable->new_state_base[*state] + rest; |
2029 | } |
2030 | |
2031 | /// Decodes a single FSE symbol and updates the offset |
2032 | static inline u8 FSE_decode_symbol(const FSE_dtable *const dtable, |
2033 | u16 *const state, const u8 *const src, |
2034 | i64 *const offset) { |
2035 | const u8 symb = FSE_peek_symbol(dtable, *state); |
2036 | FSE_update_state(dtable, state, src, offset); |
2037 | return symb; |
2038 | } |
2039 | |
2040 | static inline void FSE_init_state(const FSE_dtable *const dtable, |
2041 | u16 *const state, const u8 *const src, |
2042 | i64 *const offset) { |
2043 | // Read in a full `accuracy_log` bits to initialize the state |
2044 | const u8 bits = dtable->accuracy_log; |
2045 | *state = STREAM_read_bits(src, bits, offset); |
2046 | } |
2047 | |
2048 | static size_t FSE_decompress_interleaved2(const FSE_dtable *const dtable, |
2049 | ostream_t *const out, |
2050 | istream_t *const in) { |
2051 | const size_t len = IO_istream_len(in); |
2052 | if (len == 0) { |
2053 | INP_SIZE(); |
2054 | } |
2055 | const u8 *const src = IO_get_read_ptr(in, len); |
2056 | |
2057 | // "Each bitstream must be read backward, that is starting from the end down |
2058 | // to the beginning. Therefore it's necessary to know the size of each |
2059 | // bitstream. |
2060 | // |
2061 | // It's also necessary to know exactly which bit is the latest. This is |
2062 | // detected by a final bit flag : the highest bit of latest byte is a |
2063 | // final-bit-flag. Consequently, a last byte of 0 is not possible. And the |
2064 | // final-bit-flag itself is not part of the useful bitstream. Hence, the |
2065 | // last byte contains between 0 and 7 useful bits." |
2066 | const int padding = 8 - highest_set_bit(src[len - 1]); |
2067 | i64 offset = len * 8 - padding; |
2068 | |
2069 | u16 state1, state2; |
2070 | // "The first state (State1) encodes the even indexed symbols, and the |
2071 | // second (State2) encodes the odd indexes. State1 is initialized first, and |
2072 | // then State2, and they take turns decoding a single symbol and updating |
2073 | // their state." |
2074 | FSE_init_state(dtable, &state1, src, &offset); |
2075 | FSE_init_state(dtable, &state2, src, &offset); |
2076 | |
2077 | // Decode until we overflow the stream |
2078 | // Since we decode in reverse order, overflowing the stream is offset going |
2079 | // negative |
2080 | size_t symbols_written = 0; |
2081 | while (1) { |
2082 | // "The number of symbols to decode is determined by tracking bitStream |
2083 | // overflow condition: If updating state after decoding a symbol would |
2084 | // require more bits than remain in the stream, it is assumed the extra |
2085 | // bits are 0. Then, the symbols for each of the final states are |
2086 | // decoded and the process is complete." |
2087 | IO_write_byte(out, FSE_decode_symbol(dtable, &state1, src, &offset)); |
2088 | symbols_written++; |
2089 | if (offset < 0) { |
2090 | // There's still a symbol to decode in state2 |
2091 | IO_write_byte(out, FSE_peek_symbol(dtable, state2)); |
2092 | symbols_written++; |
2093 | break; |
2094 | } |
2095 | |
2096 | IO_write_byte(out, FSE_decode_symbol(dtable, &state2, src, &offset)); |
2097 | symbols_written++; |
2098 | if (offset < 0) { |
2099 | // There's still a symbol to decode in state1 |
2100 | IO_write_byte(out, FSE_peek_symbol(dtable, state1)); |
2101 | symbols_written++; |
2102 | break; |
2103 | } |
2104 | } |
2105 | |
2106 | return symbols_written; |
2107 | } |
2108 | |
2109 | static void FSE_init_dtable(FSE_dtable *const dtable, |
2110 | const i16 *const norm_freqs, const int num_symbs, |
2111 | const int accuracy_log) { |
2112 | if (accuracy_log > FSE_MAX_ACCURACY_LOG) { |
2113 | ERROR("FSE accuracy too large"); |
2114 | } |
2115 | if (num_symbs > FSE_MAX_SYMBS) { |
2116 | ERROR("Too many symbols for FSE"); |
2117 | } |
2118 | |
2119 | dtable->accuracy_log = accuracy_log; |
2120 | |
2121 | const size_t size = (size_t)1 << accuracy_log; |
2122 | dtable->symbols = malloc(size * sizeof(u8)); |
2123 | dtable->num_bits = malloc(size * sizeof(u8)); |
2124 | dtable->new_state_base = malloc(size * sizeof(u16)); |
2125 | |
2126 | if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { |
2127 | BAD_ALLOC(); |
2128 | } |
2129 | |
2130 | // Used to determine how many bits need to be read for each state, |
2131 | // and where the destination range should start |
2132 | // Needs to be u16 because max value is 2 * max number of symbols, |
2133 | // which can be larger than a byte can store |
2134 | u16 state_desc[FSE_MAX_SYMBS]; |
2135 | |
2136 | // "Symbols are scanned in their natural order for "less than 1" |
2137 | // probabilities. Symbols with this probability are being attributed a |
2138 | // single cell, starting from the end of the table. These symbols define a |
2139 | // full state reset, reading Accuracy_Log bits." |
2140 | int high_threshold = size; |
2141 | for (int s = 0; s < num_symbs; s++) { |
2142 | // Scan for low probability symbols to put at the top |
2143 | if (norm_freqs[s] == -1) { |
2144 | dtable->symbols[--high_threshold] = s; |
2145 | state_desc[s] = 1; |
2146 | } |
2147 | } |
2148 | |
2149 | // "All remaining symbols are sorted in their natural order. Starting from |
2150 | // symbol 0 and table position 0, each symbol gets attributed as many cells |
2151 | // as its probability. Cell allocation is spread, not linear." |
2152 | // Place the rest in the table |
2153 | const u16 step = (size >> 1) + (size >> 3) + 3; |
2154 | const u16 mask = size - 1; |
2155 | u16 pos = 0; |
2156 | for (int s = 0; s < num_symbs; s++) { |
2157 | if (norm_freqs[s] <= 0) { |
2158 | continue; |
2159 | } |
2160 | |
2161 | state_desc[s] = norm_freqs[s]; |
2162 | |
2163 | for (int i = 0; i < norm_freqs[s]; i++) { |
2164 | // Give `norm_freqs[s]` states to symbol s |
2165 | dtable->symbols[pos] = s; |
2166 | // "A position is skipped if already occupied, typically by a "less |
2167 | // than 1" probability symbol." |
2168 | do { |
2169 | pos = (pos + step) & mask; |
2170 | } while (pos >= |
2171 | high_threshold); |
2172 | // Note: no other collision checking is necessary as `step` is |
2173 | // coprime to `size`, so the cycle will visit each position exactly |
2174 | // once |
2175 | } |
2176 | } |
2177 | if (pos != 0) { |
2178 | CORRUPTION(); |
2179 | } |
2180 | |
2181 | // Now we can fill baseline and num bits |
2182 | for (size_t i = 0; i < size; i++) { |
2183 | u8 symbol = dtable->symbols[i]; |
2184 | u16 next_state_desc = state_desc[symbol]++; |
2185 | // Fills in the table appropriately, next_state_desc increases by symbol |
2186 | // over time, decreasing number of bits |
2187 | dtable->num_bits[i] = (u8)(accuracy_log - highest_set_bit(next_state_desc)); |
2188 | // Baseline increases until the bit threshold is passed, at which point |
2189 | // it resets to 0 |
2190 | dtable->new_state_base[i] = |
2191 | ((u16)next_state_desc << dtable->num_bits[i]) - size; |
2192 | } |
2193 | } |
2194 | |
2195 | /// Decode an FSE header as defined in the Zstandard format specification and |
2196 | /// use the decoded frequencies to initialize a decoding table. |
2197 | static void FSE_decode_header(FSE_dtable *const dtable, istream_t *const in, |
2198 | const int max_accuracy_log) { |
2199 | // "An FSE distribution table describes the probabilities of all symbols |
2200 | // from 0 to the last present one (included) on a normalized scale of 1 << |
2201 | // Accuracy_Log . |
2202 | // |
2203 | // It's a bitstream which is read forward, in little-endian fashion. It's |
2204 | // not necessary to know its exact size, since it will be discovered and |
2205 | // reported by the decoding process. |
2206 | if (max_accuracy_log > FSE_MAX_ACCURACY_LOG) { |
2207 | ERROR("FSE accuracy too large"); |
2208 | } |
2209 | |
2210 | // The bitstream starts by reporting on which scale it operates. |
2211 | // Accuracy_Log = low4bits + 5. Note that maximum Accuracy_Log for literal |
2212 | // and match lengths is 9, and for offsets is 8. Higher values are |
2213 | // considered errors." |
2214 | const int accuracy_log = 5 + IO_read_bits(in, 4); |
2215 | if (accuracy_log > max_accuracy_log) { |
2216 | ERROR("FSE accuracy too large"); |
2217 | } |
2218 | |
2219 | // "Then follows each symbol value, from 0 to last present one. The number |
2220 | // of bits used by each field is variable. It depends on : |
2221 | // |
2222 | // Remaining probabilities + 1 : example : Presuming an Accuracy_Log of 8, |
2223 | // and presuming 100 probabilities points have already been distributed, the |
2224 | // decoder may read any value from 0 to 255 - 100 + 1 == 156 (inclusive). |
2225 | // Therefore, it must read log2sup(156) == 8 bits. |
2226 | // |
2227 | // Value decoded : small values use 1 less bit : example : Presuming values |
2228 | // from 0 to 156 (inclusive) are possible, 255-156 = 99 values are remaining |
2229 | // in an 8-bits field. They are used this way : first 99 values (hence from |
2230 | // 0 to 98) use only 7 bits, values from 99 to 156 use 8 bits. " |
2231 | |
2232 | i32 remaining = 1 << accuracy_log; |
2233 | i16 frequencies[FSE_MAX_SYMBS]; |
2234 | |
2235 | int symb = 0; |
2236 | while (remaining > 0 && symb < FSE_MAX_SYMBS) { |
2237 | // Log of the number of possible values we could read |
2238 | int bits = highest_set_bit(remaining + 1) + 1; |
2239 | |
2240 | u16 val = IO_read_bits(in, bits); |
2241 | |
2242 | // Try to mask out the lower bits to see if it qualifies for the "small |
2243 | // value" threshold |
2244 | const u16 lower_mask = ((u16)1 << (bits - 1)) - 1; |
2245 | const u16 threshold = ((u16)1 << bits) - 1 - (remaining + 1); |
2246 | |
2247 | if ((val & lower_mask) < threshold) { |
2248 | IO_rewind_bits(in, 1); |
2249 | val = val & lower_mask; |
2250 | } else if (val > lower_mask) { |
2251 | val = val - threshold; |
2252 | } |
2253 | |
2254 | // "Probability is obtained from Value decoded by following formula : |
2255 | // Proba = value - 1" |
2256 | const i16 proba = (i16)val - 1; |
2257 | |
2258 | // "It means value 0 becomes negative probability -1. -1 is a special |
2259 | // probability, which means "less than 1". Its effect on distribution |
2260 | // table is described in next paragraph. For the purpose of calculating |
2261 | // cumulated distribution, it counts as one." |
2262 | remaining -= proba < 0 ? -proba : proba; |
2263 | |
2264 | frequencies[symb] = proba; |
2265 | symb++; |
2266 | |
2267 | // "When a symbol has a probability of zero, it is followed by a 2-bits |
2268 | // repeat flag. This repeat flag tells how many probabilities of zeroes |
2269 | // follow the current one. It provides a number ranging from 0 to 3. If |
2270 | // it is a 3, another 2-bits repeat flag follows, and so on." |
2271 | if (proba == 0) { |
2272 | // Read the next two bits to see how many more 0s |
2273 | int repeat = IO_read_bits(in, 2); |
2274 | |
2275 | while (1) { |
2276 | for (int i = 0; i < repeat && symb < FSE_MAX_SYMBS; i++) { |
2277 | frequencies[symb++] = 0; |
2278 | } |
2279 | if (repeat == 3) { |
2280 | repeat = IO_read_bits(in, 2); |
2281 | } else { |
2282 | break; |
2283 | } |
2284 | } |
2285 | } |
2286 | } |
2287 | IO_align_stream(in); |
2288 | |
2289 | // "When last symbol reaches cumulated total of 1 << Accuracy_Log, decoding |
2290 | // is complete. If the last symbol makes cumulated total go above 1 << |
2291 | // Accuracy_Log, distribution is considered corrupted." |
2292 | if (remaining != 0 || symb >= FSE_MAX_SYMBS) { |
2293 | CORRUPTION(); |
2294 | } |
2295 | |
2296 | // Initialize the decoding table using the determined weights |
2297 | FSE_init_dtable(dtable, frequencies, symb, accuracy_log); |
2298 | } |
2299 | |
2300 | static void FSE_init_dtable_rle(FSE_dtable *const dtable, const u8 symb) { |
2301 | dtable->symbols = malloc(sizeof(u8)); |
2302 | dtable->num_bits = malloc(sizeof(u8)); |
2303 | dtable->new_state_base = malloc(sizeof(u16)); |
2304 | |
2305 | if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { |
2306 | BAD_ALLOC(); |
2307 | } |
2308 | |
2309 | // This setup will always have a state of 0, always return symbol `symb`, |
2310 | // and never consume any bits |
2311 | dtable->symbols[0] = symb; |
2312 | dtable->num_bits[0] = 0; |
2313 | dtable->new_state_base[0] = 0; |
2314 | dtable->accuracy_log = 0; |
2315 | } |
2316 | |
2317 | static void FSE_free_dtable(FSE_dtable *const dtable) { |
2318 | free(dtable->symbols); |
2319 | free(dtable->num_bits); |
2320 | free(dtable->new_state_base); |
2321 | memset(dtable, 0, sizeof(FSE_dtable)); |
2322 | } |
2323 | /******* END FSE PRIMITIVES ***************************************************/ |