[PATCH 7/12] generic ffs()

Akinobu Mita
2006-01-26T03:35:16Z

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

HAVE_ARCH_FFS_BITOPS is defined when the architecture has its own
version of these functions.

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
@@ -418,13 +418,45 @@

#endif /* HAVE_ARCH_SCHED_BITOPS */

+#ifndef HAVE_ARCH_FFS_BITOPS
+
/*
* ffs: find first bit set. This is defined the same way as
* the libc and compiler builtin ffs routines, therefore
* differs in spirit from the above ffz (man ffs).
*/

-#define ffs(x) generic_ffs(x)
+static inline int ffs(int x)
+{
+ int r = 1;
+
+ if (!x)
+ return 0;
+ if (!(x & 0xffff)) {
+ x >>= 16;
+ r += 16;
+ }
+ if (!(x & 0xff)) {
+ x >>= 8;
+ r += 8;
+ }
+ if (!(x & 0xf)) {
+ x >>= 4;
+ r += 4;
+ }
+ if (!(x & 3)) {
+ x >>= 2;
+ r += 2;
+ }
+ if (!(x & 1)) {
+ x >>= 1;
+ r += 1;
+ }
+ return r;
+}
+
+#endif /* HAVE_ARCH_FFS_BITOPS */
+

/*
* hweightN: returns the hamming weight (i.e. the number