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Merge pull request #415 from lz4/fasterDecodingXp

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Faster decoding xp
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Yann Collet 2017-11-01 09:58:49 -07:00 committed by GitHub
commit cc4a109b0d
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 27 additions and 9 deletions
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36
lib/lz4.c
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@ -1146,7 +1146,7 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
int partialDecoding, /* full, partial */
int targetOutputSize, /* only used if partialDecoding==partial */
int dict, /* noDict, withPrefix64k, usingExtDict */
const BYTE* const lowPrefix, /* == dst when no prefix */
const BYTE* const lowPrefix, /* always <= dst, == dst when no prefix */
const BYTE* const dictStart, /* only if dict==usingExtDict */
const size_t dictSize /* note : = 0 if noDict */
)
@ -1160,15 +1160,15 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
BYTE* oexit = op + targetOutputSize;
const BYTE* const dictEnd = (const BYTE*)dictStart + dictSize;
const unsigned dec32table[] = {0, 1, 2, 1, 4, 4, 4, 4};
const int dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
const unsigned inc32table[8] = {0, 1, 2, 1, 0, 4, 4, 4};
const int dec64table[8] = {0, 0, 0, -1, -4, 1, 2, 3};
const int safeDecode = (endOnInput==endOnInputSize);
const int checkOffset = ((safeDecode) && (dictSize < (int)(64 KB)));
/* Special cases */
if ((partialDecoding) && (oexit > oend-MFLIMIT)) oexit = oend-MFLIMIT; /* targetOutputSize too high => decode everything */
if ((partialDecoding) && (oexit > oend-MFLIMIT)) oexit = oend-MFLIMIT; /* targetOutputSize too high => just decode everything */
if ((endOnInput) && (unlikely(outputSize==0))) return ((srcSize==1) && (*ip==0)) ? 0 : -1; /* Empty output buffer */
if ((!endOnInput) && (unlikely(outputSize==0))) return (*ip==0?1:-1);
@ -1178,8 +1178,27 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
const BYTE* match;
size_t offset;
/* get literal length */
unsigned const token = *ip++;
/* shortcut for common case :
* in most circumstances, we expect to decode small matches (<= 18 bytes) separated by few literals (<= 14 bytes).
* this shortcut was tested on x86 and x64, where it improves decoding speed.
* it has not yet been benchmarked on ARM, Power, mips, etc. */
if (((ip + 14 /*maxLL*/ + 2 /*offset*/ <= iend)
& (op + 14 /*maxLL*/ + 18 /*maxML*/ <= oend))
& ((token < (15<<ML_BITS)) & ((token & ML_MASK) != 15)) ) {
size_t const ll = token >> ML_BITS;
size_t const off = LZ4_readLE16(ip+ll);
const BYTE* const matchPtr = op + ll - off; /* pointer underflow risk ? */
if ((off >= 18) /* do not deal with overlapping matches */ & (matchPtr >= lowPrefix)) {
size_t const ml = (token & ML_MASK) + MINMATCH;
memcpy(op, ip, 16); op += ll; ip += ll + 2 /*offset*/;
memcpy(op, matchPtr, 18); op += ml;
continue;
}
}
/* decode literal length */
if ((length=(token>>ML_BITS)) == RUN_MASK) {
unsigned s;
do {
@ -1257,14 +1276,13 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
/* copy match within block */
cpy = op + length;
if (unlikely(offset<8)) {
const int dec64 = dec64table[offset];
op[0] = match[0];
op[1] = match[1];
op[2] = match[2];
op[3] = match[3];
match += dec32table[offset];
match += inc32table[offset];
memcpy(op+4, match, 4);
match -= dec64;
match -= dec64table[offset];
} else { LZ4_copy8(op, match); match+=8; }
op += 8;
@ -1281,7 +1299,7 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
LZ4_copy8(op, match);
if (length>16) LZ4_wildCopy(op+8, match+8, cpy);
}
op=cpy; /* correction */
op = cpy; /* correction */
}
/* end of decoding */