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bitops: use unsigned char pointer for SIMD scan arithmetic

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Refactor redisBitposScanAVX512/AVX2 to take unsigned char *p instead of
unsigned long *l, replacing the repeated (unsigned long*)((unsigned char*)l + N)
casts with simple p += N pointer arithmetic.

At the call sites, work with the existing 'c' char pointer throughout the
SIMD phase and cast to unsigned long * only once before the scalar tail loop.
This commit is contained in:
Martin Dimitrov 2026-05-19 20:36:48 -07:00
parent 7303abecb7
commit afb8a2bbc4
1 changed files with 12 additions and 12 deletions
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24
src/bitops.c
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@ -390,17 +390,17 @@ static inline long long redisPopcountAuto(const unsigned char *p, long count) {
* ----------------------------------------------------------------------- */
#ifdef HAVE_AVX512
ATTRIBUTE_TARGET_AVX512
static unsigned long redisBitposScanAVX512(unsigned long *l,
static unsigned long redisBitposScanAVX512(unsigned char *p,
unsigned long count, int bit) {
unsigned long scanned = 0;
__m512i skip = bit ? _mm512_setzero_si512()
: _mm512_set1_epi64(-1LL);
while (count >= 64) {
__m512i data = _mm512_loadu_si512(l);
__m512i data = _mm512_loadu_si512(p);
__mmask8 eq = _mm512_cmpeq_epi64_mask(data, skip);
if (eq != 0xFF) break;
l = (unsigned long *)((unsigned char *)l + 64);
p += 64;
count -= 64;
scanned += 64;
}
@ -410,17 +410,17 @@ static unsigned long redisBitposScanAVX512(unsigned long *l,
#ifdef HAVE_AVX2
ATTRIBUTE_TARGET_AVX2
static unsigned long redisBitposScanAVX2(unsigned long *l,
static unsigned long redisBitposScanAVX2(unsigned char *p,
unsigned long count, int bit) {
unsigned long scanned = 0;
__m256i skip = bit ? _mm256_setzero_si256()
: _mm256_set1_epi8((char)0xFF);
while (count >= 32) {
__m256i data = _mm256_loadu_si256((__m256i *)l);
__m256i data = _mm256_loadu_si256((__m256i *)p);
int eq = _mm256_movemask_epi8(_mm256_cmpeq_epi8(data, skip));
if (eq != -1) break;
l = (unsigned long *)((unsigned char *)l + 32);
p += 32;
count -= 32;
scanned += 32;
}
@ -468,7 +468,6 @@ long long redisBitpos(void *s, unsigned long count, int bit) {
/* Skip bits with full word step. Use SIMD when available for the
* bulk of the scan, then fall through to scalar for the tail. */
l = (unsigned long*) c;
if (!found) {
skipval = bit ? 0 : ULONG_MAX;
@ -478,8 +477,8 @@ long long redisBitpos(void *s, unsigned long count, int bit) {
#if defined(HAVE_AVX512)
if (BITOP_USE_AVX512 && count >= 64) {
unsigned long advanced = redisBitposScanAVX512(l, count, bit);
l = (unsigned long*)((unsigned char*)l + advanced);
unsigned long advanced = redisBitposScanAVX512(c, count, bit);
c += advanced;
count -= advanced;
pos += advanced * 8;
useAVX = 1;
@ -488,8 +487,8 @@ long long redisBitpos(void *s, unsigned long count, int bit) {
#if defined(HAVE_AVX2)
if (!useAVX && BITOP_USE_AVX2 && count >= 32) {
unsigned long advanced = redisBitposScanAVX2(l, count, bit);
l = (unsigned long*)((unsigned char*)l + advanced);
unsigned long advanced = redisBitposScanAVX2(c, count, bit);
c += advanced;
count -= advanced;
pos += advanced * 8;
}
@ -497,12 +496,14 @@ long long redisBitpos(void *s, unsigned long count, int bit) {
/* Scalar word-at-a-time scan handles the tail after SIMD and
* serves as the sole scan path when SIMD is unavailable. */
l = (unsigned long *)c;
while (count >= sizeof(*l)) {
if (*l != skipval) break;
l++;
count -= sizeof(*l);
pos += sizeof(*l)*8;
}
c = (unsigned char *)l;
}
/* Load bytes into "word" considering the first byte as the most significant
@ -512,7 +513,6 @@ long long redisBitpos(void *s, unsigned long count, int bit) {
*
* Note that the loading is designed to work even when the bytes left
* (count) are less than a full word. We pad it with zero on the right. */
c = (unsigned char*)l;
for (j = 0; j < sizeof(*l); j++) {
word <<= 8;
if (count) {