[PATCH 4/12] generic fls() and fls64()

Akinobu Mita
2006-01-26T03:32:36Z

This patch introduces the C-language equivalent of the function:
int fls(int x);
int fls64(__u64 x);

HAVE_ARCH_FLS_BITOPS is defined when the architecture has its own
fls().
HAVE_ARCH_FLS64_BITOPS is defined when the architecture has its own
fls64()

This code largely copied from:
include/linux/bitops.h

Index: 2.6-git/include/asm-generic/bitops.h
=================================--- 2.6-git.orig/include/asm-generic/bitops.h 2006-01-25 19:14:10.000000000 +0900
+++ 2.6-git/include/asm-generic/bitops.h 2006-01-25 19:14:10.000000000 +0900
@@ -237,12 +237,54 @@

#endif /* HAVE_ARCH_FFZ_BITOPS */

+#ifndef HAVE_ARCH_FLS_BITOPS
+
/*
* fls: find last bit set.
*/

-#define fls(x) generic_fls(x)
-#define fls64(x) generic_fls64(x)
+static __inline__ int fls(int x)
+{
+ int r = 32;
+
+ if (!x)
+ return 0;
+ if (!(x & 0xffff0000u)) {
+ x <<= 16;
+ r -= 16;
+ }
+ if (!(x & 0xff000000u)) {
+ x <<= 8;
+ r -= 8;
+ }
+ if (!(x & 0xf0000000u)) {
+ x <<= 4;
+ r -= 4;
+ }
+ if (!(x & 0xc0000000u)) {
+ x <<= 2;
+ r -= 2;
+ }
+ if (!(x & 0x80000000u)) {
+ x <<= 1;
+ r -= 1;
+ }
+ return r;
+}
+
+#endif /* HAVE_ARCH_FLS_BITOPS */
+
+#ifndef HAVE_ARCH_FLS64_BITOPS
+
+static inline int fls64(__u64 x)
+{
+ __u32 h = x >> 32;
+ if (h)
+ return fls(x) + 32;
+ return fls(x);
+}
+
+#endif /* HAVE_ARCH_FLS64_BITOPS */

#ifdef __KERNEL__