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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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10
include/asm-ia64/gcc_intrin.h
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@@ -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) \
({ \