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Extend Dictionary Matches Backwards

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W. Felix Handte
2018-06-13 14:58:36 -04:00
parent d53a04211c
commit b82063b266
1 changed files with 11 additions and 3 deletions
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lib/compress/zstd_lazy.c
+8
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@@ -685,9 +685,17 @@ size_t ZSTD_compressBlock_lazy_generic(
*/ */
/* catch up */ /* catch up */
if (offset) { if (offset) {
if (dictMode == ZSTD_noDict) {
while ( ((start > anchor) & (start - (offset-ZSTD_REP_MOVE) > prefixLowest)) while ( ((start > anchor) & (start - (offset-ZSTD_REP_MOVE) > prefixLowest))
&& (start[-1] == (start-(offset-ZSTD_REP_MOVE))[-1]) ) /* only search for offset within prefix */ && (start[-1] == (start-(offset-ZSTD_REP_MOVE))[-1]) ) /* only search for offset within prefix */
{ start--; matchLength++; } { start--; matchLength++; }
}
if (dictMode == ZSTD_dictMatchState) {
U32 const matchIndex = (U32)((start-base) - (offset - ZSTD_REP_MOVE));
const BYTE* match = (matchIndex < prefixLowestIndex) ? dictBase + matchIndex - dictIndexDelta : base + matchIndex;
const BYTE* const mStart = (matchIndex < prefixLowestIndex) ? dictLowest : prefixLowest;
while ((start>anchor) && (match>mStart) && (start[-1] == match[-1])) { start--; match--; matchLength++; } /* catch up */
}
offset_2 = offset_1; offset_1 = (U32)(offset - ZSTD_REP_MOVE); offset_2 = offset_1; offset_1 = (U32)(offset - ZSTD_REP_MOVE);
} }
/* store sequence */ /* store sequence */