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bigint.c (lzb): use __builtin_clz() if available.

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This commit is contained in:
Yukihiro "Matz" Matsumoto
2022-07-11 08:01:52 +09:00
parent 3046440b5a
commit 95610a292b
1 changed files with 10 additions and 2 deletions
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mrbgems/mruby-bigint/core/bigint.c
+10 -2
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@@ -329,11 +329,19 @@ mpz_mul_int(mrb_state *mrb, mpz_t *x, mpz_t *y, mrb_int n)
/* number of leading zero bits in digit */
static int
lzb(mp_limb a)
lzb(mp_limb x)
{
#if (defined(__GNUC__) || __has_builtin(__builtin_clz))
/* subtract 2 because DIGITBITS = LONGBITS-2 */
if (sizeof(mp_limb) == sizeof(long long))
return __builtin_clzll(x)-2;
else if (sizeof(mp_limb) == sizeof(int))
return __builtin_clz(x)-2;
#endif
mp_limb i; int j=0;
for (i = ((mp_limb)1 << (DIGITBITS-1)); i && !(a&i) ; j++,i>>=1)
for (i = ((mp_limb)1 << (DIGITBITS-1)); i && !(x&i) ; j++,i>>=1)
;
return j;
}