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minor refactor zstd_fast

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make hot variables more local
This commit is contained in:
Yann Collet
2024-10-07 11:22:40 -07:00
parent e8fce38954
commit 1e7fa242f4
2 changed files with 36 additions and 39 deletions
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lib/compress/zstd_compress_internal.h
+3 -1
View File
@@ -560,7 +560,9 @@ MEM_STATIC int ZSTD_cParam_withinBounds(ZSTD_cParameter cParam, int value)
/* ZSTD_selectAddr:
* @return a >= b ? trueAddr : falseAddr,
* tries to force branchless codegen. */
MEM_STATIC const BYTE* ZSTD_selectAddr(U32 a, U32 b, const BYTE* trueAddr, const BYTE* falseAddr) {
MEM_STATIC const BYTE*
ZSTD_selectAddr(U32 a, U32 b, const BYTE* trueAddr, const BYTE* falseAddr)
{
#if defined(__GNUC__) && defined(__x86_64__)
__asm__ (
"cmp %1, %2\n"
lib/compress/zstd_fast.c
+9 -14
View File
@@ -166,7 +166,6 @@ size_t ZSTD_compressBlock_fast_noDict_generic(
* we load from here instead of from tables, if the index is invalid.
* Used to avoid unpredictable branches. */
const BYTE dummy[] = {0x12,0x34,0x56,0x78,0x9a,0xbc,0xde,0xf0,0xe2,0xb4};
const BYTE *mvalAddr;
const BYTE* anchor = istart;
const BYTE* ip0 = istart;
@@ -182,7 +181,6 @@ size_t ZSTD_compressBlock_fast_noDict_generic(
size_t hash0; /* hash for ip0 */
size_t hash1; /* hash for ip1 */
U32 idx; /* match idx for ip0 */
U32 mval; /* src value at match idx */
U32 offcode;
const BYTE* match0;
@@ -255,23 +253,22 @@ _start: /* Requires: ip0 */
* However expression below complies into conditional move. Since
* match is unlikely and we only *branch* on idxl0 > prefixLowestIndex
* if there is a match, all branches become predictable. */
mvalAddr = base + idx;
mvalAddr = ZSTD_selectAddr(idx, prefixStartIndex, mvalAddr, &dummy[0]);
{ const BYTE* mvalAddr = ZSTD_selectAddr(idx, prefixStartIndex, base + idx, &dummy[0]);
/* load match for ip[0] */
mval = MEM_read32(mvalAddr);
U32 const mval = MEM_read32(mvalAddr);
/* check match at ip[0] */
if (MEM_read32(ip0) == mval && idx >= prefixStartIndex) {
/* found a match! */
/* First write next hash table entry; we've already calculated it.
* This write is known to be safe because the ip1 == ip0 + 1, so
* we know we will resume searching after ip1 */
/* Write next hash table entry (it's already calculated).
* This write is known to be safe because the ip1 == ip0 + 1,
* so searching will resume after ip1 */
hashTable[hash1] = (U32)(ip1 - base);
goto _offset;
}
}
/* lookup ip[1] */
idx = hashTable[hash1];
@@ -289,12 +286,9 @@ _start: /* Requires: ip0 */
current0 = (U32)(ip0 - base);
hashTable[hash0] = current0;
mvalAddr = base + idx;
mvalAddr = ZSTD_selectAddr(idx, prefixStartIndex, mvalAddr, &dummy[0]);
{ const BYTE* mvalAddr = ZSTD_selectAddr(idx, prefixStartIndex, base + idx, &dummy[0]);
/* load match for ip[0] */
mval = MEM_read32(mvalAddr);
U32 const mval = MEM_read32(mvalAddr);
/* check match at ip[0] */
if (MEM_read32(ip0) == mval && idx >= prefixStartIndex) {
@@ -316,6 +310,7 @@ _start: /* Requires: ip0 */
goto _offset;
}
}
/* lookup ip[1] */
idx = hashTable[hash1];