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updated double_fast complementary insertion 

in a way which is more favorable to compression ratio,
though very slightly slower (~-1%).

More details in the PR.
dev
Yann Collet 2019-07-11 15:25:22 -07:00
parent b01c1c679f
commit d1327738c2
1 changed files with 35 additions and 11 deletions
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46
lib/compress/zstd_double_fast.c
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@ -254,11 +254,23 @@ _match_stored:
anchor = ip;
if (ip <= ilimit) {
/* Fill Table */
hashLong[ZSTD_hashPtr(base+current+2, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(base+current+2, hBitsS, mls)] = current+2; /* here because current+2 could be > iend-8 */
hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(ip-2, hBitsS, mls)] = (U32)(ip-2-base);
/* Complementary insertion */
/* done after iLimit test, as candidates could be > iend-8 */
{ U32 const indexToInsert = current+2;
hashLong[ZSTD_hashPtr(base+indexToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(base+indexToInsert, hBitsS, mls)] =
indexToInsert;
}
{ const BYTE* const ipToInsert = ip - 2;
hashLong[ZSTD_hashPtr(ipToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(ipToInsert, hBitsS, mls)] =
(U32)(ipToInsert-base);
}
{ const BYTE* const ipToInsert = ip - 1;
hashLong[ZSTD_hashPtr(ipToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(ipToInsert, hBitsS, mls)] =
(U32)(ipToInsert-base);
}
/* check immediate repcode */
if (dictMode == ZSTD_dictMatchState) {
@ -452,16 +464,28 @@ static size_t ZSTD_compressBlock_doubleFast_extDict_generic(
continue;
} }
/* found a match : store it */
/* move to next sequence start */
ip += mLength;
anchor = ip;
if (ip <= ilimit) {
/* Fill Table */
hashSmall[ZSTD_hashPtr(base+current+2, hBitsS, mls)] = current+2;
hashLong[ZSTD_hashPtr(base+current+2, hBitsL, 8)] = current+2;
hashSmall[ZSTD_hashPtr(ip-2, hBitsS, mls)] = (U32)(ip-2-base);
hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] = (U32)(ip-2-base);
/* Complementary insertion */
/* done after iLimit test, as candidates could be > iend-8 */
{ U32 const indexToInsert = current+2;
hashLong[ZSTD_hashPtr(base+indexToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(base+indexToInsert, hBitsS, mls)] =
indexToInsert;
}
{ const BYTE* const ipToInsert = ip - 2;
hashLong[ZSTD_hashPtr(ipToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(ipToInsert, hBitsS, mls)] =
(U32)(ipToInsert-base);
}
{ const BYTE* const ipToInsert = ip - 1;
hashLong[ZSTD_hashPtr(ipToInsert, hBitsL, 8)] =
hashSmall[ZSTD_hashPtr(ipToInsert, hBitsS, mls)] =
(U32)(ipToInsert-base);
}
/* check immediate repcode */
while (ip <= ilimit) {
U32 const current2 = (U32)(ip-base);