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| author | Kevin Ryde <user42@zip.com.au> | 2001-01-18 22:23:26 +0100 |
|---|---|---|
| committer | Kevin Ryde <user42@zip.com.au> | 2001-01-18 22:23:26 +0100 |
| commit | e92dae8cfb78de5a3ac49a8f2763f8540adbeff6 (patch) | |
| tree | 9240fd7831c37ffd9057797cc274f705dbaa782c /longlong.h | |
| parent | cc46cc009fd37e3ed95409b4b635975a89806f6a (diff) | |
| download | gmp-e92dae8cfb78de5a3ac49a8f2763f8540adbeff6.tar.gz | |
(pentium count_trailing_zeros): Use count_leading_zeros.
Diffstat (limited to 'longlong.h')
| -rw-r--r-- | longlong.h | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/longlong.h b/longlong.h index 93f708d6a..a5a9b7d60 100644 --- a/longlong.h +++ b/longlong.h @@ -538,6 +538,11 @@ extern USItype __MPN(udiv_qrnnd) _PROTO ((USItype *, USItype, USItype, USItype)) #define COUNT_LEADING_ZEROS_NEED_CLZ_TAB #define COUNT_LEADING_ZEROS_0 31 /* n==0 indistinguishable from n==1 */ +/* count_trailing_zeros for pentium is done by the generic code below using + count_leading_zeros. This should be a fixed 15 or 16 cycles, possibly + plus an L1 miss. P5 "bsfl" on the other hand takes between 18 and 42 + depending where the least significant 1 bit is. */ + #else #define count_leading_zeros(count, x) \ do { \ @@ -546,13 +551,12 @@ extern USItype __MPN(udiv_qrnnd) _PROTO ((USItype *, USItype, USItype, USItype)) __asm__ ("bsrl %1,%0" : "=r" (__cbtmp) : "rm" ((USItype)(x))); \ (count) = __cbtmp ^ 31; \ } while (0) -#endif - #define count_trailing_zeros(count, x) \ do { \ ASSERT ((x) != 0); \ __asm__ ("bsfl %1,%0" : "=r" (count) : "rm" ((USItype)(x))); \ } while (0) +#endif #ifndef UMUL_TIME #define UMUL_TIME 10 |