[PATCH 7/12] generic ffs()

From: Akinobu Mita <mita_at_miraclelinux.com>
Date: 2006-01-26 14:35:16
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
-
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Received on Thu Jan 26 14:35:45 2006

This archive was generated by hypermail 2.1.8 : 2006-01-26 14:35:52 EST