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Support decompression of compressed blocks of size ZSTD_BLOCKSIZE_MAX exactly

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This commit is contained in:
Yann Collet 2022-12-22 12:40:27 -08:00
parent f5ea3a196f
commit ea2895cef4
2 changed files with 14 additions and 2 deletions
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4
lib/compress/zstd_compress.c
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@ -2770,6 +2770,10 @@ ZSTD_entropyCompressSeqStore(
if (cSize >= maxCSize) return 0; /* block not compressed */
}
DEBUGLOG(5, "ZSTD_entropyCompressSeqStore() cSize: %zu", cSize);
/* libzstd decoder before > v1.5.4 is not compatible with compressed blocks of size ZSTD_BLOCKSIZE_MAX exactly.
* This restriction is indirectly already fulfilled by respecting ZSTD_minGain() condition above.
*/
assert(cSize < ZSTD_BLOCKSIZE_MAX);
return cSize;
}

12
lib/decompress/zstd_decompress_block.c
View File

@ -2010,12 +2010,20 @@ ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx,
* Offsets are long if they are larger than 2^STREAM_ACCUMULATOR_MIN.
* We don't expect that to be the case in 64-bit mode.
* In block mode, window size is not known, so we have to be conservative.
* (note: but it could be evaluated from current-lowLimit)
* (note: it could possibly be evaluated from current-lowLimit)
*/
ZSTD_longOffset_e const isLongOffset = (ZSTD_longOffset_e)(MEM_32bits() && (!frame || (dctx->fParams.windowSize > (1ULL << STREAM_ACCUMULATOR_MIN))));
DEBUGLOG(5, "ZSTD_decompressBlock_internal (size : %u)", (U32)srcSize);
RETURN_ERROR_IF(srcSize >= ZSTD_BLOCKSIZE_MAX, srcSize_wrong, "");
/* Note : the wording of the specification
* allows compressed block to be sized exactly ZSTD_BLOCKSIZE_MAX.
* This generally does not happen, as it makes little sense,
* since an uncompressed block would feature same size and have no decompression cost.
* Also, note that decoder from reference libzstd before < v1.5.4
* would consider this edge case as an error.
* As a consequence, avoid generating compressed blocks of size ZSTD_BLOCKSIZE_MAX
* for broader compatibility with the deployed ecosystem of zstd decoders */
RETURN_ERROR_IF(srcSize > ZSTD_BLOCKSIZE_MAX, srcSize_wrong, "");
/* Decode literals section */
{ size_t const litCSize = ZSTD_decodeLiteralsBlock(dctx, src, srcSize, dst, dstCapacity, streaming);