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diff --git a/deps/libchdr/deps/zstd-1.5.5/contrib/seekable_format/zstd_seekable.h b/deps/libchdr/deps/zstd-1.5.5/contrib/seekable_format/zstd_seekable.h
new file mode 100644
index 00000000..a0e5e357
--- /dev/null
+++ b/deps/libchdr/deps/zstd-1.5.5/contrib/seekable_format/zstd_seekable.h
@@ -0,0 +1,226 @@
+#ifndef SEEKABLE_H
+#define SEEKABLE_H
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
+#include <stdio.h>
+#include "zstd.h"   /* ZSTDLIB_API */
+
+
+#define ZSTD_seekTableFooterSize 9
+
+#define ZSTD_SEEKABLE_MAGICNUMBER 0x8F92EAB1
+
+#define ZSTD_SEEKABLE_MAXFRAMES 0x8000000U
+
+/* Limit maximum size to avoid potential issues storing the compressed size */
+#define ZSTD_SEEKABLE_MAX_FRAME_DECOMPRESSED_SIZE 0x40000000U
+
+/*-****************************************************************************
+*  Seekable Format
+*
+*  The seekable format splits the compressed data into a series of "frames",
+*  each compressed individually so that decompression of a section in the
+*  middle of an archive only requires zstd to decompress at most a frame's
+*  worth of extra data, instead of the entire archive.
+******************************************************************************/
+
+typedef struct ZSTD_seekable_CStream_s ZSTD_seekable_CStream;
+typedef struct ZSTD_seekable_s ZSTD_seekable;
+typedef struct ZSTD_seekTable_s ZSTD_seekTable;
+
+/*-****************************************************************************
+*  Seekable compression - HowTo
+*  A ZSTD_seekable_CStream object is required to tracking streaming operation.
+*  Use ZSTD_seekable_createCStream() and ZSTD_seekable_freeCStream() to create/
+*  release resources.
+*
+*  Streaming objects are reusable to avoid allocation and deallocation,
+*  to start a new compression operation call ZSTD_seekable_initCStream() on the
+*  compressor.
+*
+*  Data streamed to the seekable compressor will automatically be split into
+*  frames of size `maxFrameSize` (provided in ZSTD_seekable_initCStream()),
+*  or if none is provided, will be cut off whenever ZSTD_seekable_endFrame() is
+*  called or when the default maximum frame size (2GB) is reached.
+*
+*  Use ZSTD_seekable_initCStream() to initialize a ZSTD_seekable_CStream object
+*  for a new compression operation.
+*  - `maxFrameSize` indicates the size at which to automatically start a new
+*            seekable frame.
+*            `maxFrameSize == 0` implies the default maximum size.
+*            Smaller frame sizes allow faster decompression of small segments,
+*            since retrieving a single byte requires decompression of
+*            the full frame where the byte belongs.
+*            In general, size the frames to roughly correspond to
+*            the access granularity (when it's known).
+*            But small sizes also reduce compression ratio.
+*            Avoid really tiny frame sizes (< 1 KB),
+*            that would hurt compression ratio considerably.
+*  - `checksumFlag` indicates whether or not the seek table should include frame
+*            checksums on the uncompressed data for verification.
+*  @return : a size hint for input to provide for compression, or an error code
+*            checkable with ZSTD_isError()
+*
+*  Use ZSTD_seekable_compressStream() repetitively to consume input stream.
+*  The function will automatically update both `pos` fields.
+*  Note that it may not consume the entire input, in which case `pos < size`,
+*  and it's up to the caller to present again remaining data.
+*  @return : a size hint, preferred nb of bytes to use as input for next
+*            function call or an error code, which can be tested using
+*            ZSTD_isError().
+*            Note 1 : it's just a hint, to help latency a little, any other
+*                     value will work fine.
+*
+*  At any time, call ZSTD_seekable_endFrame() to end the current frame and
+*  start a new one.
+*
+*  ZSTD_seekable_endStream() will end the current frame, and then write the seek
+*  table so that decompressors can efficiently find compressed frames.
+*  ZSTD_seekable_endStream() may return a number > 0 if it was unable to flush
+*  all the necessary data to `output`.  In this case, it should be called again
+*  until all remaining data is flushed out and 0 is returned.
+******************************************************************************/
+
+/*===== Seekable compressor management =====*/
+ZSTDLIB_API ZSTD_seekable_CStream* ZSTD_seekable_createCStream(void);
+ZSTDLIB_API size_t ZSTD_seekable_freeCStream(ZSTD_seekable_CStream* zcs);
+
+/*===== Seekable compression functions =====*/
+ZSTDLIB_API size_t ZSTD_seekable_initCStream(ZSTD_seekable_CStream* zcs, int compressionLevel, int checksumFlag, unsigned maxFrameSize);
+ZSTDLIB_API size_t ZSTD_seekable_compressStream(ZSTD_seekable_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
+ZSTDLIB_API size_t ZSTD_seekable_endFrame(ZSTD_seekable_CStream* zcs, ZSTD_outBuffer* output);
+ZSTDLIB_API size_t ZSTD_seekable_endStream(ZSTD_seekable_CStream* zcs, ZSTD_outBuffer* output);
+
+/*= Raw seek table API
+ *  These functions allow for the seek table to be constructed directly.
+ *  This table can then be appended to a file of concatenated frames.
+ *  This allows the frames to be compressed independently, even in parallel,
+ *  and compiled together afterward into a seekable archive.
+ *
+ *  Use ZSTD_seekable_createFrameLog() to allocate and initialize a tracking
+ *  structure.
+ *
+ *  Call ZSTD_seekable_logFrame() once for each frame in the archive.
+ *  checksum is optional, and will not be used if checksumFlag was 0 when the
+ *  frame log was created.  If present, it should be the least significant 32
+ *  bits of the XXH64 hash of the uncompressed data.
+ *
+ *  Call ZSTD_seekable_writeSeekTable to serialize the data into a seek table.
+ *  If the entire table was written, the return value will be 0.  Otherwise,
+ *  it will be equal to the number of bytes left to write. */
+typedef struct ZSTD_frameLog_s ZSTD_frameLog;
+ZSTDLIB_API ZSTD_frameLog* ZSTD_seekable_createFrameLog(int checksumFlag);
+ZSTDLIB_API size_t ZSTD_seekable_freeFrameLog(ZSTD_frameLog* fl);
+ZSTDLIB_API size_t ZSTD_seekable_logFrame(ZSTD_frameLog* fl, unsigned compressedSize, unsigned decompressedSize, unsigned checksum);
+ZSTDLIB_API size_t ZSTD_seekable_writeSeekTable(ZSTD_frameLog* fl, ZSTD_outBuffer* output);
+
+
+/*-****************************************************************************
+*  Seekable decompression - HowTo
+*  A ZSTD_seekable object is required to tracking the seekTable.
+*
+*  Call ZSTD_seekable_init* to initialize a ZSTD_seekable object with the
+*  the seek table provided in the input.
+*  There are three modes for ZSTD_seekable_init:
+*    - ZSTD_seekable_initBuff() : An in-memory API.  The data contained in
+*      `src` should be the entire seekable file, including the seek table.
+*      `src` should be kept alive and unmodified until the ZSTD_seekable object
+*      is freed or reset.
+*    - ZSTD_seekable_initFile() : A simplified file API using stdio.  fread and
+*      fseek will be used to access the required data for building the seek
+*      table and doing decompression operations.  `src` should not be closed
+*      or modified until the ZSTD_seekable object is freed or reset.
+*    - ZSTD_seekable_initAdvanced() : A general API allowing the client to
+*      provide its own read and seek callbacks.
+*        + ZSTD_seekable_read() : read exactly `n` bytes into `buffer`.
+*                                 Premature EOF should be treated as an error.
+*        + ZSTD_seekable_seek() : seek the read head to `offset` from `origin`,
+*                                 where origin is either SEEK_SET (beginning of
+*                                 file), or SEEK_END (end of file).
+*  Both functions should return a non-negative value in case of success, and a
+*  negative value in case of failure.  If implementing using this API and
+*  stdio, be careful with files larger than 4GB and fseek.  All of these
+*  functions return an error code checkable with ZSTD_isError().
+*
+*  Call ZSTD_seekable_decompress to decompress `dstSize` bytes at decompressed
+*  offset `offset`.  ZSTD_seekable_decompress may have to decompress the entire
+*  prefix of the frame before the desired data if it has not already processed
+*  this section. If ZSTD_seekable_decompress is called multiple times for a
+*  consecutive range of data, it will efficiently retain the decompressor object
+*  and avoid redecompressing frame prefixes.  The return value is the number of
+*  bytes decompressed, or an error code checkable with ZSTD_isError().
+*
+*  The seek table access functions can be used to obtain the data contained
+*  in the seek table.  If frameIndex is larger than the value returned by
+*  ZSTD_seekable_getNumFrames(), they will return error codes checkable with
+*  ZSTD_isError().  Note that since the offset access functions return
+*  unsigned long long instead of size_t, in this case they will instead return
+*  the value ZSTD_SEEKABLE_FRAMEINDEX_TOOLARGE.
+******************************************************************************/
+
+/*===== Seekable decompressor management =====*/
+ZSTDLIB_API ZSTD_seekable* ZSTD_seekable_create(void);
+ZSTDLIB_API size_t ZSTD_seekable_free(ZSTD_seekable* zs);
+
+/*===== Seekable decompression functions =====*/
+ZSTDLIB_API size_t ZSTD_seekable_initBuff(ZSTD_seekable* zs, const void* src, size_t srcSize);
+ZSTDLIB_API size_t ZSTD_seekable_initFile(ZSTD_seekable* zs, FILE* src);
+ZSTDLIB_API size_t ZSTD_seekable_decompress(ZSTD_seekable* zs, void* dst, size_t dstSize, unsigned long long offset);
+ZSTDLIB_API size_t ZSTD_seekable_decompressFrame(ZSTD_seekable* zs, void* dst, size_t dstSize, unsigned frameIndex);
+
+#define ZSTD_SEEKABLE_FRAMEINDEX_TOOLARGE (0ULL-2)
+/*===== Seekable seek table access functions =====*/
+ZSTDLIB_API unsigned ZSTD_seekable_getNumFrames(const ZSTD_seekable* zs);
+ZSTDLIB_API unsigned long long ZSTD_seekable_getFrameCompressedOffset(const ZSTD_seekable* zs, unsigned frameIndex);
+ZSTDLIB_API unsigned long long ZSTD_seekable_getFrameDecompressedOffset(const ZSTD_seekable* zs, unsigned frameIndex);
+ZSTDLIB_API size_t ZSTD_seekable_getFrameCompressedSize(const ZSTD_seekable* zs, unsigned frameIndex);
+ZSTDLIB_API size_t ZSTD_seekable_getFrameDecompressedSize(const ZSTD_seekable* zs, unsigned frameIndex);
+ZSTDLIB_API unsigned ZSTD_seekable_offsetToFrameIndex(const ZSTD_seekable* zs, unsigned long long offset);
+
+
+/*-****************************************************************************
+*  Direct exploitation of the seekTable
+*
+*  Memory constrained use cases that manage multiple archives
+*  benefit from retaining multiple archive seek tables
+*  without retaining a ZSTD_seekable instance for each.
+*
+*  Below API allow the above-mentioned use cases
+*  to initialize a ZSTD_seekable, extract its (smaller) ZSTD_seekTable,
+*  then throw the ZSTD_seekable away to save memory.
+*
+*  Standard ZSTD operations can then be used
+*  to decompress frames based on seek table offsets.
+******************************************************************************/
+
+/*===== Independent seek table management =====*/
+ZSTDLIB_API ZSTD_seekTable* ZSTD_seekTable_create_fromSeekable(const ZSTD_seekable* zs);
+ZSTDLIB_API size_t ZSTD_seekTable_free(ZSTD_seekTable* st);
+
+/*===== Direct seek table access functions =====*/
+ZSTDLIB_API unsigned ZSTD_seekTable_getNumFrames(const ZSTD_seekTable* st);
+ZSTDLIB_API unsigned long long ZSTD_seekTable_getFrameCompressedOffset(const ZSTD_seekTable* st, unsigned frameIndex);
+ZSTDLIB_API unsigned long long ZSTD_seekTable_getFrameDecompressedOffset(const ZSTD_seekTable* st, unsigned frameIndex);
+ZSTDLIB_API size_t ZSTD_seekTable_getFrameCompressedSize(const ZSTD_seekTable* st, unsigned frameIndex);
+ZSTDLIB_API size_t ZSTD_seekTable_getFrameDecompressedSize(const ZSTD_seekTable* st, unsigned frameIndex);
+ZSTDLIB_API unsigned ZSTD_seekTable_offsetToFrameIndex(const ZSTD_seekTable* st, unsigned long long offset);
+
+
+/*===== Seekable advanced I/O API =====*/
+typedef int(ZSTD_seekable_read)(void* opaque, void* buffer, size_t n);
+typedef int(ZSTD_seekable_seek)(void* opaque, long long offset, int origin);
+typedef struct {
+    void* opaque;
+    ZSTD_seekable_read* read;
+    ZSTD_seekable_seek* seek;
+} ZSTD_seekable_customFile;
+ZSTDLIB_API size_t ZSTD_seekable_initAdvanced(ZSTD_seekable* zs, ZSTD_seekable_customFile src);
+
+#if defined (__cplusplus)
+}
+#endif
+
+#endif