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Remove long range matcher immediate repcode check 

The compression ratio gets about 0.01% worse on the files I tested, but the
code is much simpler.
dev
Nick Terrell 2018-02-21 19:30:05 -08:00
parent af866b3a58
commit 7e2bf4ebad
1 changed files with 0 additions and 70 deletions
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70
lib/compress/zstd_ldm.c
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@ -514,14 +514,7 @@ size_t ZSTD_ldm_blockCompress(rawSeq const* sequences, size_t nbSeq,
{ {
ZSTD_blockCompressor const blockCompressor = ZSTD_blockCompressor const blockCompressor =
ZSTD_selectBlockCompressor(cParams->strategy, extDict); ZSTD_selectBlockCompressor(cParams->strategy, extDict);
int const doImmediateRepCheck = cParams->strategy < ZSTD_btopt;
/* Prefix and extDict parameters */
U32 const dictLimit = ms->dictLimit;
U32 const lowestIndex = extDict ? ms->lowLimit : dictLimit;
BYTE const* const base = ms->base; BYTE const* const base = ms->base;
BYTE const* const dictBase = extDict ? ms->dictBase : NULL;
BYTE const* const dictEnd = extDict ? dictBase + dictLimit : NULL;
BYTE const* const lowPrefixPtr = base + dictLimit;
/* Input bounds */ /* Input bounds */
BYTE const* const istart = (BYTE const*)src; BYTE const* const istart = (BYTE const*)src;
BYTE const* const iend = istart + srcSize; BYTE const* const iend = istart + srcSize;
@ -558,69 +551,6 @@ size_t ZSTD_ldm_blockCompress(rawSeq const* sequences, size_t nbSeq,
sequence.matchLength - MINMATCH); sequence.matchLength - MINMATCH);
ip += sequence.matchLength; ip += sequence.matchLength;
} }
/* Check immediate repcode */
if (doImmediateRepCheck) {
rawSeq* nextSeq = (seq + 1 < *nbSeq) ? &sequences[seq + 1] : NULL;
/* Allow repcodes up to the next predefined sequence */
BYTE const* const repCheckEnd = nextSeq
? ip + nextSeq->litLength
: iend;
BYTE const* const repCheckLimit = repCheckEnd - HASH_READ_SIZE;
assert(repCheckEnd <= iend);
if (extDict) {
while (ip < repCheckLimit) {
U32 const current = (U32)(ip-base);
U32 const repIndex = current - rep[1];
const BYTE* repMatch = repIndex < dictLimit ?
dictBase + repIndex : base + repIndex;
if ( (((U32)((dictLimit-1) - repIndex) >= 3) &
(repIndex > lowestIndex)) /* intentional overflow */
&& (MEM_read32(repMatch) == MEM_read32(ip)) ) {
const BYTE* const repEnd = repIndex < dictLimit ?
dictEnd : repCheckEnd;
size_t const rLength = ZSTD_count_2segments(
ip+4, repMatch+4, repCheckEnd, repEnd,
lowPrefixPtr) + 4;
/* Swap rep[1] <=> rep[0] */
U32 const tmpOffset = rep[1];
rep[1] = rep[0];
rep[0] = tmpOffset;
ZSTD_storeSeq(seqStore, 0, ip, 0, rLength-MINMATCH);
ip += rLength;
if (nextSeq) {
assert(nextSeq->litLength >= rLength);
nextSeq->litLength -= rLength;
}
continue;
}
break;
}
} else {
while ( (ip < repCheckLimit)
&& ( (rep[1] > 0) && (rep[1] <= (U32)(ip - lowPrefixPtr))
&& (MEM_read32(ip) == MEM_read32(ip - rep[1])) )) {
size_t const rLength = ZSTD_count(ip+4, ip+4-rep[1],
repCheckEnd) + 4;
/* Swap rep[1] <=> rep[0] */
{
U32 const tmpOff = rep[1];
rep[1] = rep[0];
rep[0] = tmpOff;
}
ZSTD_storeSeq(seqStore, 0, ip, 0, rLength-MINMATCH);
ip += rLength;
if (nextSeq) {
assert(nextSeq->litLength >= rLength);
nextSeq->litLength -= rLength;
}
}
}
}
} }
ZSTD_ldm_limitTableUpdate(ms, ip); ZSTD_ldm_limitTableUpdate(ms, ip);
ZSTD_ldm_fillFastTables(ms, cParams, ip); ZSTD_ldm_fillFastTables(ms, cParams, ip);