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[IA64] fix fls()

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The ia64-version of fls() never worked as intended (the bitnumbering
was off by 1 and fls(0) was undefined).  This patch fixes the problem
by using a popcnt-based fls(), which on McKinley-derived cores is
slightly faster than both ia64_fls() and generic_fls().  The resulting
code, however, is bigger (7-8 bundles instead of about 3 bundles).
Also switch ia64_popcnt() to __builtin_popcountl() for GCC v3.4 or
newer since the compiler can predicate that and schedule it better.

Thanks to Simon Derr and Matt Mackall for tracking down this bug.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
David Mosberger-Tang 2005-04-21 11:07:59 -07:00 committed by Tony Luck
parent d8470b7c13
commit 821376bf15
2 changed files with 24 additions and 7 deletions
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21
include/asm-ia64/bitops.h
View File

@ -314,8 +314,8 @@ __ffs (unsigned long x)
#ifdef __KERNEL__
/*
* find_last_zero_bit - find the last zero bit in a 64 bit quantity
* @x: The value to search
* Return bit number of last (most-significant) bit set. Undefined
* for x==0. Bits are numbered from 0..63 (e.g., ia64_fls(9) == 3).
*/
static inline unsigned long
ia64_fls (unsigned long x)
@ -327,10 +327,23 @@ ia64_fls (unsigned long x)
return exp - 0xffff;
}
/*
* Find the last (most significant) bit set. Returns 0 for x==0 and
* bits are numbered from 1..32 (e.g., fls(9) == 4).
*/
static inline int
fls (int x)
fls (int t)
{
return ia64_fls((unsigned int) x);
unsigned long x = t & 0xffffffffu;
if (!x)
return 0;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return ia64_popcnt(x);
}
/*

10
include/asm-ia64/gcc_intrin.h
View File

@ -133,13 +133,17 @@ register unsigned long ia64_r13 asm ("r13") __attribute_used__;
ia64_intri_res; \
})
#define ia64_popcnt(x) \
({ \
#if __GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
# define ia64_popcnt(x) __builtin_popcountl(x)
#else
# define ia64_popcnt(x) \
({ \
__u64 ia64_intri_res; \
asm ("popcnt %0=%1" : "=r" (ia64_intri_res) : "r" (x)); \
\
ia64_intri_res; \
})
})
#endif
#define ia64_getf_exp(x) \
({ \