linux-kernel - [PATCH V2] blackfin: optimize ffz, __ffs, ffs, _

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Message-Id: <1460708588-16867-1-git-send-email-zengzhaoxiu@163.com>
Date:	Fri, 15 Apr 2016 16:23:08 +0800
From:	zengzhaoxiu@....com
To:	linux-kernel@...r.kernel.org
Cc:	Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
	Steven Miao <realmz6@...il.com>,
	adi-buildroot-devel@...ts.sourceforge.net
Subject: [PATCH V2] blackfin: optimize ffz, __ffs, ffs, __fls, and fls functions

From: Zhaoxiu Zeng <zhaoxiu.zeng@...il.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@...il.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