[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>
diff --git a/include/asm-ia64/bitops.h b/include/asm-ia64/bitops.h
index 925d54c..7232528 100644
--- a/include/asm-ia64/bitops.h
+++ b/include/asm-ia64/bitops.h
@@ -314,8 +314,8 @@
#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 @@
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);
}
/*
diff --git a/include/asm-ia64/gcc_intrin.h b/include/asm-ia64/gcc_intrin.h
index 7c357df..4fb4e43 100644
--- a/include/asm-ia64/gcc_intrin.h
+++ b/include/asm-ia64/gcc_intrin.h
@@ -133,13 +133,17 @@
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) \
({ \