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* src/hash.c (jhash_string): Help the compiler optimize the hash

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Invoke memcpy() with a constant length, where possible.

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This commit is contained in:
Justine Tunney 2022-11-06 12:13:21 -05:00 committed by Paul Smith
parent 6b45f89adb
commit 090d99dd2d
1 changed files with 13 additions and 7 deletions
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20
src/hash.c
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@ -361,7 +361,7 @@ round_up_2 (unsigned long n)
#define sum_get_unaligned_32(r, p) \
do { \
unsigned int val; \
memcpy(&val, (p), 4); \
memcpy (&val, (p), 4); \
r += val; \
} while(0);
@ -413,13 +413,16 @@ jhash(unsigned const char *k, int length)
#define UINTSZ sizeof (unsigned int)
#ifdef WORDS_BIGENDIAN
/* The ifs are ordered from the first byte in memory to the last. */
/* The ifs are ordered from the first byte in memory to the last.
Help the compiler optimize by using static memcpy length. */
#define sum_up_to_nul(r, p, plen, flag) \
do { \
unsigned int val = 0; \
size_t pn = (plen); \
size_t n = pn < UINTSZ ? pn : UINTSZ; \
memcpy (&val, (p), n); \
if (pn >= UINTSZ) \
memcpy (&val, (p), UINTSZ); \
else \
memcpy (&val, (p), pn); \
if ((val & 0xFF000000) == 0) \
flag = 1; \
else if ((val & 0xFF0000) == 0) \
@ -432,13 +435,16 @@ jhash(unsigned const char *k, int length)
#else
/* First detect the presence of zeroes. If there is none, we can
sum the 4 bytes directly. Otherwise, the ifs are ordered as in the
big endian case, from the first byte in memory to the last. */
big endian case, from the first byte in memory to the last.
Help the compiler optimize by using static memcpy length. */
#define sum_up_to_nul(r, p, plen, flag) \
do { \
unsigned int val = 0; \
size_t pn = (plen); \
size_t n = pn < UINTSZ ? pn : UINTSZ; \
memcpy (&val, (p), n); \
if (pn >= UINTSZ) \
memcpy (&val, (p), UINTSZ); \
else \
memcpy (&val, (p), pn); \
flag = ((val - 0x01010101) & ~val) & 0x80808080; \
if (!flag) \
r += val; \