On 1 May 2003, Falk Hueffner wrote:
>
> There appears to be hardware support for fls, too. This is what gcc
> generates for
Yeah, except if you want best code generation you should probably use
static inline int fls(int x)
{
int bit;
/* Only well-defined for non-zero */
asm("bsrl %1,%0":"=r" (bit):"rm" (x));
return x ? bit : 32;
}
which should generate (assuming you give "-march=xxxx" to tell gcc to use
cmov):
movl $32, %eax
bsrl %edx,%ecx
testl %edx, %edx
cmovne %ecx, %eax
which looks pretty optimal.
Linus
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This archive was generated by hypermail 2b29 : Wed Apr 30 2003 - 22:00:37 EST