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fixed LZ4HC_countPattern()

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- works with byte values other than `0`
- works for any repetitive pattern of length 1, 2 or 4 (but not 3!)
- works for little and big endian systems
- preserve speed of previous implementation
This commit is contained in:
Yann Collet 2017-11-07 10:53:29 -08:00
parent aa99163752
commit a004c1fbee
1 changed files with 19 additions and 5 deletions
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24
lib/lz4hc.c
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@ -130,20 +130,34 @@ static int LZ4HC_countBack(const BYTE* const ip, const BYTE* const match,
return back;
}
static unsigned LZ4HC_countPattern(const BYTE* ip, const BYTE* const iEnd, reg_t pattern)
/* LZ4HC_countPattern() :
* pattern32 must be a sample of repetitive pattern of length 1, 2 or 4 (but not 3!) */
static unsigned LZ4HC_countPattern(const BYTE* ip, const BYTE* const iEnd, U32 const pattern32)
{
const BYTE* const iStart = ip;
reg_t const pattern = (sizeof(pattern)==8) ? (reg_t)pattern32 + (((reg_t)pattern32) << 32) : pattern32;
while (likely(ip<iEnd-(sizeof(pattern)-1))) {
while (likely(ip < iEnd-(sizeof(pattern)-1))) {
reg_t const diff = LZ4_read_ARCH(ip) ^ pattern;
if (!diff) { ip+=sizeof(pattern); continue; }
ip += LZ4_NbCommonBytes(diff);
return (unsigned)(ip - iStart);
}
if ((sizeof(pattern)==8) && (ip<(iEnd-3)) && (LZ4_read32(ip)==(U32)pattern)) { ip+=4; }
if ((ip<(iEnd-1)) && (LZ4_read16(ip)==(U16)pattern)) { ip+=2; }
if ((ip<iEnd) && (*ip == (BYTE)pattern)) ip++;
if (LZ4_isLittleEndian()) {
reg_t patternByte = pattern;
while ((ip<iEnd) && (*ip == (BYTE)patternByte)) {
ip++; patternByte >>= 8;
}
} else { /* big endian */
U32 bitOffset = (sizeof(pattern)*8) - 8;
while (ip < iEnd) {
BYTE const byte = (BYTE)(pattern >> bitOffset);
if (*ip != byte) break;
ip ++; bitOffset -= 8;
}
}
return (unsigned)(ip - iStart);
}