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Code Issues Releases 1 Activity

slightly improved ratio at -22

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merging of repcode search into btsearch introduced a small compression ratio regressio at max level :
1.3.2 : 52728769
after repMerge patch : 52760789 (+32020)

A few minor changes have produced this difference.
They can be hard to spot.

This patch buys back about half of the difference,
by no longer inserting position at hc3 when a long match is found there.
It feels strangely counter-intuitive, but works :
after this patch : 52742555 (-18234)
This commit is contained in:
Yann Collet
2017-11-19 13:39:12 -08:00
parent 99435dbbab
commit 42c1e64270
3 changed files with 16 additions and 13 deletions
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10
lib/compress/zstd_opt.c
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@ -263,7 +263,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
U32 const windowLow = zc->lowLimit;
U32* smallerPtr = bt + 2*(current&btMask);
U32* largerPtr = bt + 2*(current&btMask) + 1;
U32 matchEndIdx = current+8; /* farthest referenced position of any match => detects repetitive patterns */
U32 matchEndIdx = current+8+1; /* farthest referenced position of any match => detects repetitive patterns */
U32 dummy32; /* to be nullified at the end */
U32 mnum = 0;
@ -328,8 +328,9 @@ U32 ZSTD_insertBtAndGetAllMatches (
matches[0].off = (current - matchIndex3) + ZSTD_REP_MOVE;
matches[0].len = (U32)mlen;
mnum = 1;
if ( (mlen > sufficient_len)
| (ip+mlen == iLimit) ) { /* best possible */
if ( (mlen > sufficient_len) |
(ip+mlen == iLimit) ) { /* best possible length */
zc->nextToUpdate = current+1; /* skip insertion */
return 1;
} } } }
@ -387,7 +388,8 @@ U32 ZSTD_insertBtAndGetAllMatches (
*smallerPtr = *largerPtr = 0;
zc->nextToUpdate = (matchEndIdx > current + 8) ? matchEndIdx - 8 : current+1; /* skip repetitive patterns */
assert(matchEndIdx > current+8);
zc->nextToUpdate = matchEndIdx - 8; /* skip repetitive patterns */
return mnum;
}