Re: [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random

David Mosberger
2005-04-09T00:21:06Z

Here is a first cut for the patch. It compiles with gcc 3.3 and 3.4
and boots on Ski. Assuming nobody finds any issues, I'll make a final
patch tonight.

Thanks,

--david

=== include/asm-ia64/bitops.h 1.19 vs edited ==--- 1.19/include/asm-ia64/bitops.h 2005-03-13 15:30:06 -08:00
+++ edited/include/asm-ia64/bitops.h 2005-04-08 17:17:09 -07:00
@@ -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);
}

/*
=== include/asm-ia64/gcc_intrin.h 1.7 vs edited ==--- 1.7/include/asm-ia64/gcc_intrin.h 2004-10-05 11:27:40 -07:00
+++ edited/include/asm-ia64/gcc_intrin.h 2005-04-08 17:16:54 -07:00
@@ -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) \
({ \