[PATCH 3/6] FRV: Optimise ffs()

David Howells
2006-09-13T13:03:06Z

From: David Howells <dhowells@redhat.com>

Optimise ffs(x) by using fls(x & x - 1) which we optimise to use the SCAN
instruction.

Signed-Off-By: David Howells <dhowells@redhat.com>
---

include/asm-frv/bitops.h | 33 +++++++++++++++++++++++++++++++--
1 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/include/asm-frv/bitops.h b/include/asm-frv/bitops.h
index 591eecc..1f70d47 100644
--- a/include/asm-frv/bitops.h
+++ b/include/asm-frv/bitops.h
@@ -157,8 +157,6 @@ (__builtin_constant_p(nr) ? \
__constant_test_bit((nr),(addr)) : \
__test_bit((nr),(addr)))

-#include <asm-generic/bitops/ffs.h>
-#include <asm-generic/bitops/__ffs.h>
#include <asm-generic/bitops/find.h>

/**
@@ -227,6 +225,37 @@ int fls64(u64 n)

}

+/**
+ * ffs - find first bit set
+ * @x: the word to search
+ *
+ * - return 32..1 to indicate bit 31..0 most least significant bit set
+ * - return 0 to indicate no bits set
+ */
+static inline __attribute__((const))
+int ffs(int x)
+{
+ /* Note: (x & -x) gives us a mask that is the least significant
+ * (rightmost) 1-bit of the value in x.
+ */
+ return fls(x & -x);
+}
+
+/**
+ * __ffs - find first bit set
+ * @x: the word to search
+ *
+ * - return 31..0 to indicate bit 31..0 most least significant bit set
+ * - if no bits are set in x, the result is undefined
+ */
+static inline __attribute__((const))
+int __ffs(unsigned long x)
+{
+ int bit;
+ asm("scan %1,gr0,%0" : "=r"(bit) : "r"(x & -x));
+ return 31 - bit;
+}
+
#include <asm-generic/bitops/sched.h>
#include <asm-generic/bitops/hweight.h>