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Subject[PATCH V2] blackfin: optimize ffz, __ffs, ffs, __fls, and fls functions
Date
From: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>

blackfin has popcount instruction (ONES), we can do the efficient
computing (ffz, __ffs, ffs, __fls, and fls) use this instruction.

Adapted from "https://en.wikipedia.org/wiki/Find_first_set" and
arch/ia64/include/asm/bitops.h.

Changes to V1:
- Use hweight32 instead __arch_hweight32

Signed-off-by: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
---
arch/blackfin/include/asm/bitops.h | 73 +++++++++++++++++++++++++++++++++++---
1 file changed, 68 insertions(+), 5 deletions(-)

diff --git a/arch/blackfin/include/asm/bitops.h b/arch/blackfin/include/asm/bitops.h
index b298b65..602e7c0 100644
--- a/arch/blackfin/include/asm/bitops.h
+++ b/arch/blackfin/include/asm/bitops.h
@@ -9,10 +9,6 @@

#include <linux/compiler.h>

-#include <asm-generic/bitops/__ffs.h>
-#include <asm-generic/bitops/ffz.h>
-#include <asm-generic/bitops/fls.h>
-#include <asm-generic/bitops/__fls.h>
#include <asm-generic/bitops/fls64.h>
#include <asm-generic/bitops/find.h>

@@ -21,7 +17,6 @@
#endif

#include <asm-generic/bitops/sched.h>
-#include <asm-generic/bitops/ffs.h>
#include <asm-generic/bitops/const_hweight.h>
#include <asm-generic/bitops/lock.h>

@@ -137,4 +132,72 @@ static inline unsigned int __arch_hweight8(unsigned int w)
return __arch_hweight32(w & 0xff);
}

+/**
+ * ffz - find the first zero bit in a long word
+ * @x: The long word to find the bit in
+ *
+ * Returns the bit-number (0..31) of the first (least significant) zero bit.
+ * Undefined if no zero exists, so code should check against ~0UL first...
+ */
+static inline unsigned long ffz(unsigned long x)
+{
+ return hweight32(x & (~x - 1));
+}
+
+/**
+ * ffs - find first bit set
+ * @x: the word to search
+ *
+ * This is defined the same way as
+ * the libc and compiler builtin ffs routines, therefore
+ * differs in spirit from the above ffz (man ffs).
+ */
+static inline int ffs(int x)
+{
+ if (!x)
+ return 0;
+ return hweight32(x ^ ((unsigned int)x - 1));
+}
+
+/**
+ * __ffs - find first bit in word.
+ * @x: The word to search
+ *
+ * Undefined if no bit exists, so code should check against 0 first.
+ */
+static inline unsigned long __ffs(unsigned long x)
+{
+ return hweight32(~x & (x - 1));
+}
+
+/*
+ * 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)
+{
+ if (!x)
+ return 0;
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ return hweight32(x);
+}
+
+/*
+ * Find the last (most significant) bit set. Undefined for x==0.
+ * Bits are numbered from 0..31 (e.g., __fls(9) == 3).
+ */
+static inline unsigned long __fls(unsigned long x)
+{
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ return hweight32(x) - 1;
+}
+
#endif /* _BLACKFIN_BITOPS_H */
--
2.5.0

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