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Undo my previous commit and do it differently. Break the ffs() etc macros

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into two parts - one to do the bsfl and the other to convert the result
(base 0) to ffs()-like (base 1) in inline C.  This enables the optimizer
to be a lot smarter in certain cases, like where it knows that the argument
is non-zero and we want ffs(known non zero arg) - 1.  This appears to
produce identical code to the old inline when the argument is unknown.
This commit is contained in:
Peter Wemm 1999-08-19 14:54:40 +00:00
parent ac7cc2e469
commit 264c3d8738
2 changed files with 54 additions and 28 deletions
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41
sys/amd64/include/cpufunc.h
View File

@ -30,7 +30,7 @@
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id: cpufunc.h,v 1.88 1999/07/23 23:45:19 alc Exp $
* $Id: cpufunc.h,v 1.89 1999/08/19 00:32:48 peter Exp $
*/
/*
@ -82,40 +82,53 @@ enable_intr(void)
__asm __volatile("sti");
}
#define HAVE_INLINE_FFS
#if __GNUC__ == 2 && __GNUC_MINOR__ > 8
#define ffs(mask) __builtin_ffs(mask)
#else
#define HAVE_INLINE__BSFL
static __inline int
ffs(int mask)
__bsfl(int mask)
{
int result;
/*
* bsfl turns out to be not all that slow on 486's. It can beaten
* using a binary search to reduce to 4 bits and then a table lookup,
* but only if the code is inlined and in the cache, and the code
* is quite large so inlining it probably busts the cache.
*
*/
__asm __volatile("bsfl %0,%0" : "=r" (result) : "0" (mask));
return (result);
}
#define HAVE_INLINE_FFS
static __inline int
ffs(int mask)
{
/*
* Note that gcc-2's builtin ffs would be used if we didn't declare
* this inline or turn off the builtin. The builtin is faster but
* broken in gcc-2.4.5 and slower but working in gcc-2.5 and 2.6.
*/
__asm __volatile("testl %0,%0; je 1f; bsfl %0,%0; incl %0; 1:"
: "=r" (result) : "0" (mask));
return mask == 0 ? mask : __bsfl(mask) + 1;
}
#define HAVE_INLINE__BSRL
static __inline int
__bsrl(int mask)
{
int result;
__asm __volatile("bsrl %0,%0" : "=r" (result) : "0" (mask));
return (result);
}
#endif
#define HAVE_INLINE_FLS
static __inline int
fls(int mask)
{
int result;
__asm __volatile("testl %0,%0; je 1f; bsrl %0,%0; incl %0; 1:"
: "=r" (result) : "0" (mask));
return (result);
return mask == 0 ? mask : __bsrl(mask) + 1;
}
#if __GNUC__ < 2

41
sys/i386/include/cpufunc.h
View File

@ -30,7 +30,7 @@
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id: cpufunc.h,v 1.88 1999/07/23 23:45:19 alc Exp $
* $Id: cpufunc.h,v 1.89 1999/08/19 00:32:48 peter Exp $
*/
/*
@ -82,40 +82,53 @@ enable_intr(void)
__asm __volatile("sti");
}
#define HAVE_INLINE_FFS
#if __GNUC__ == 2 && __GNUC_MINOR__ > 8
#define ffs(mask) __builtin_ffs(mask)
#else
#define HAVE_INLINE__BSFL
static __inline int
ffs(int mask)
__bsfl(int mask)
{
int result;
/*
* bsfl turns out to be not all that slow on 486's. It can beaten
* using a binary search to reduce to 4 bits and then a table lookup,
* but only if the code is inlined and in the cache, and the code
* is quite large so inlining it probably busts the cache.
*
*/
__asm __volatile("bsfl %0,%0" : "=r" (result) : "0" (mask));
return (result);
}
#define HAVE_INLINE_FFS
static __inline int
ffs(int mask)
{
/*
* Note that gcc-2's builtin ffs would be used if we didn't declare
* this inline or turn off the builtin. The builtin is faster but
* broken in gcc-2.4.5 and slower but working in gcc-2.5 and 2.6.
*/
__asm __volatile("testl %0,%0; je 1f; bsfl %0,%0; incl %0; 1:"
: "=r" (result) : "0" (mask));
return mask == 0 ? mask : __bsfl(mask) + 1;
}
#define HAVE_INLINE__BSRL
static __inline int
__bsrl(int mask)
{
int result;
__asm __volatile("bsrl %0,%0" : "=r" (result) : "0" (mask));
return (result);
}
#endif
#define HAVE_INLINE_FLS
static __inline int
fls(int mask)
{
int result;
__asm __volatile("testl %0,%0; je 1f; bsrl %0,%0; incl %0; 1:"
: "=r" (result) : "0" (mask));
return (result);
return mask == 0 ? mask : __bsrl(mask) + 1;
}
#if __GNUC__ < 2