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Simplify DDS Hash Table Construction

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No need to walk the chainTable; we can just keep shifting the entries in the
hashTable.
This commit is contained in:
W. Felix Handte
2020-09-10 18:51:52 -04:00
parent ad9f98ac3f
commit 9e83c782f8
1 changed files with 9 additions and 4 deletions
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lib/compress/zstd_lazy.c
+9 -4
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@@ -481,17 +481,22 @@ void ZSTD_dedicatedDictSearch_lazy_loadDictionary(ZSTD_matchState_t* ms, const B
U32 const target = (U32)(ip - ms->window.base); U32 const target = (U32)(ip - ms->window.base);
U32* const chainTable = ms->chainTable; U32* const chainTable = ms->chainTable;
U32 const chainMask = (1 << ms->cParams.chainLog) - 1; U32 const chainMask = (1 << ms->cParams.chainLog) - 1;
for (U32 idx = ms->nextToUpdate; idx < target; idx++) { U32 idx = ms->nextToUpdate;
U32 bucketSize = 1 << ZSTD_LAZY_DDSS_BUCKET_LOG;
for ( ; idx < target; idx++) {
U32 i;
U32 const h = ZSTD_hashPtr( U32 const h = ZSTD_hashPtr(
ms->window.base + idx, ms->window.base + idx,
ms->cParams.hashLog - ZSTD_LAZY_DDSS_BUCKET_LOG, ms->cParams.hashLog - ZSTD_LAZY_DDSS_BUCKET_LOG,
ms->cParams.minMatch) << ZSTD_LAZY_DDSS_BUCKET_LOG; ms->cParams.minMatch) << ZSTD_LAZY_DDSS_BUCKET_LOG;
/* Shift hash cache down 1. */
for (i = bucketSize - 1; i; i--)
ms->hashTable[h + i] = ms->hashTable[h + i - 1];
/* Insert new position. */
chainTable[idx & chainMask] = ms->hashTable[h]; chainTable[idx & chainMask] = ms->hashTable[h];
ms->hashTable[h] = idx; ms->hashTable[h] = idx;
/* Same logic as before. But now, just copy the chain into the bucket */
for (U32 i = 0; i < (1 << ZSTD_LAZY_DDSS_BUCKET_LOG) - 1; i++)
ms->hashTable[h + i + 1] = chainTable[ms->hashTable[h + i] & chainMask];
} }
ms->nextToUpdate = target; ms->nextToUpdate = target;
} }