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mdbx: микро-оптимизация cmp_reverse().

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Леонид Юрьев (Leonid Yuriev)
2022-12-31 01:30:52 +03:00
parent bcddeaba9f
commit 8519fde741
2 changed files with 86 additions and 8 deletions
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54
src/core.c
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@@ -11894,16 +11894,54 @@ tail3le(const uint8_t *p, size_t l) {
/* Compare two items in reverse byte order */
__hot static int cmp_reverse(const MDBX_val *a, const MDBX_val *b) {
const size_t shortest = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
if (likely(shortest)) {
size_t left = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
if (likely(left)) {
const uint8_t *pa = ptr_disp(a->iov_base, a->iov_len);
const uint8_t *pb = ptr_disp(b->iov_base, b->iov_len);
const uint8_t *const end = pa - shortest;
do {
int diff = *--pa - *--pb;
if (likely(diff))
return diff;
} while (pa != end);
while (left >= sizeof(size_t)) {
pa -= sizeof(size_t);
pb -= sizeof(size_t);
left -= sizeof(size_t);
STATIC_ASSERT(sizeof(size_t) == 4 || sizeof(size_t) == 8);
if (sizeof(size_t) == 4) {
uint32_t xa = unaligned_peek_u32(1, pa);
uint32_t xb = unaligned_peek_u32(1, pb);
#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
xa = osal_bswap32(xa);
xb = osal_bswap32(xb);
#endif /* __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__ */
if (xa != xb)
return (xa < xb) ? -1 : 1;
} else {
uint64_t xa = unaligned_peek_u64(1, pa);
uint64_t xb = unaligned_peek_u64(1, pb);
#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
xa = osal_bswap64(xa);
xb = osal_bswap64(xb);
#endif /* __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__ */
if (xa != xb)
return (xa < xb) ? -1 : 1;
}
}
if (sizeof(size_t) == 8 && left >= 4) {
pa -= 4;
pb -= 4;
left -= 4;
uint32_t xa = unaligned_peek_u32(1, pa);
uint32_t xb = unaligned_peek_u32(1, pb);
#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
xa = osal_bswap32(xa);
xb = osal_bswap32(xb);
#endif /* __BYTE_ORDER__ != __ORDER_BIG_ENDIAN__ */
if (xa != xb)
return (xa < xb) ? -1 : 1;
}
if (left) {
unsigned xa = tail3le(pa - left, left);
unsigned xb = tail3le(pb - left, left);
if (xa != xb)
return (xa < xb) ? -1 : 1;
}
}
return CMP2INT(a->iov_len, b->iov_len);
}