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authorDavid Mosberger-Tang <davidm@hpl.hp.com>2005-04-21 11:07:59 -0700
committerTony Luck <tony.luck@intel.com>2005-04-21 11:07:59 -0700
commit821376bf15e692941f9235f13a14987009fd0b10 (patch)
tree2179380ee3eb38fb393719e6ce32b15e934c4a44 /include/asm-ia64/bitops.h
parentd8470b7c13e11c18cf14a7e3180f0b00e715e4f0 (diff)
[IA64] fix fls()
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>
Diffstat (limited to 'include/asm-ia64/bitops.h')
-rw-r--r--include/asm-ia64/bitops.h21
1 files changed, 17 insertions, 4 deletions
diff --git a/include/asm-ia64/bitops.h b/include/asm-ia64/bitops.h
index 925d54cee475..7232528e2d0c 100644
--- a/include/asm-ia64/bitops.h
+++ b/include/asm-ia64/bitops.h
@@ -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);
}
/*