lkml.org 
[lkml]   [2008]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2] x86: merge the simple bitops and move them to bitops.h
x86: merge the simple bitops and move them to bitops.h.

Some of those can be written in such a way that the same
inline assembly can be used to generate both 32 bit and
64 bit code.

For ffs and fls, x86_64 unconditionally used the cmov
instruction and i386 unconditionally used a conditional
branch over a mov instruction. In the current patch I
chose to select the version based on the availability
of the cmov instruction instead. A small detail here is
that x86_64 did not previously set CONFIG_X86_CMOV=y.

Improved comments for ffs and fls.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>

---

Hi,

Here is a new version with improved (I hope) comments for
the functions ffs and fls, suggested by Jeremy. I left
the explicit use of the -l forms in the inline assembly
of ffs and fls, because I think it is clearer that way.

Greetings,
Alexander

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 31e92fb..fb7399b 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -399,7 +399,7 @@ config X86_TSC
# generates cmov.
config X86_CMOV
def_bool y
- depends on (MK7 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7)
+ depends on (MK7 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || X86_64)

config X86_MINIMUM_CPU_FAMILY
int
diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h
index 1a23ce1..363a4ff 100644
--- a/include/asm-x86/bitops.h
+++ b/include/asm-x86/bitops.h
@@ -66,7 +66,6 @@ static inline void __set_bit(int nr, volatile void *addr)
: "Ir" (nr) : "memory");
}

-
/**
* clear_bit - Clears a bit in memory
* @nr: Bit to clear
@@ -310,6 +309,104 @@ static int test_bit(int nr, const volatile unsigned long *addr);
constant_test_bit((nr),(addr)) : \
variable_test_bit((nr),(addr)))

+/**
+ * __ffs - find first bit in word.
+ * @word: The word to search
+ *
+ * Undefined if no bit exists, so code should check against 0 first.
+ */
+static inline unsigned long __ffs(unsigned long word)
+{
+ __asm__("bsf %1,%0"
+ :"=r" (word)
+ :"rm" (word));
+ return word;
+}
+
+/**
+ * ffz - find first zero in word.
+ * @word: The word to search
+ *
+ * Undefined if no zero exists, so code should check against ~0UL first.
+ */
+static inline unsigned long ffz(unsigned long word)
+{
+ __asm__("bsf %1,%0"
+ :"=r" (word)
+ :"r" (~word));
+ return word;
+}
+
+/*
+ * __fls: find last bit set.
+ * @word: The word to search
+ *
+ * Undefined if no zero exists, so code should check against ~0UL first.
+ */
+static inline unsigned long __fls(unsigned long word)
+{
+ __asm__("bsr %1,%0"
+ :"=r" (word)
+ :"rm" (word));
+ return word;
+}
+
+#ifdef __KERNEL__
+/**
+ * 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 other bitops.
+ *
+ * ffs(value) returns 0 if value is 0 or the position of the first
+ * set bit if value is nonzero. The first (least significant) bit
+ * is at position 1.
+ */
+static inline int ffs(int x)
+{
+ int r;
+#ifdef CONFIG_X86_CMOV
+ __asm__("bsfl %1,%0\n\t"
+ "cmovzl %2,%0"
+ : "=r" (r) : "rm" (x), "r" (-1));
+#else
+ __asm__("bsfl %1,%0\n\t"
+ "jnz 1f\n\t"
+ "movl $-1,%0\n"
+ "1:" : "=r" (r) : "rm" (x));
+#endif
+ return r + 1;
+}
+
+/**
+ * fls - find last bit set
+ * @x: the word to search
+ *
+ * This is defined in a similar way as the libc and compiler builtin
+ * ffs, but returns the position of the most significant set bit.
+ *
+ * fls(value) returns 0 if value is 0 or the position of the last
+ * set bit if value is nonzero. The last (most significant) bit is
+ * at position 32.
+ */
+static inline int fls(int x)
+{
+ int r;
+#ifdef CONFIG_X86_CMOV
+ __asm__("bsrl %1,%0\n\t"
+ "cmovzl %2,%0"
+ : "=&r" (r) : "rm" (x), "rm" (-1));
+#else
+ __asm__("bsrl %1,%0\n\t"
+ "jnz 1f\n\t"
+ "movl $-1,%0\n"
+ "1:" : "=r" (r) : "rm" (x));
+#endif
+ return r + 1;
+}
+#endif /* __KERNEL__ */
+
#undef ADDR

#ifdef CONFIG_X86_32
diff --git a/include/asm-x86/bitops_32.h b/include/asm-x86/bitops_32.h
index 570f0fa..c19fbe9 100644
--- a/include/asm-x86/bitops_32.h
+++ b/include/asm-x86/bitops_32.h
@@ -38,20 +38,6 @@ static inline int find_first_zero_bit(const unsigned long *addr, unsigned size)
}

/**
- * __ffs - find first bit in word.
- * @word: The word to search
- *
- * Undefined if no bit exists, so code should check against 0 first.
- */
-static inline unsigned long __ffs(unsigned long word)
-{
- __asm__("bsfl %1,%0"
- :"=r" (word)
- :"rm" (word));
- return word;
-}
-
-/**
* find_first_bit - find the first set bit in a memory region
* @addr: The address to start the search at
* @size: The maximum size to search
@@ -72,60 +58,10 @@ static inline unsigned find_first_bit(const unsigned long *addr, unsigned size)
return x;
}

-/**
- * ffz - find first zero in word.
- * @word: The word to search
- *
- * Undefined if no zero exists, so code should check against ~0UL first.
- */
-static inline unsigned long ffz(unsigned long word)
-{
- __asm__("bsfl %1,%0"
- :"=r" (word)
- :"r" (~word));
- return word;
-}
-
#ifdef __KERNEL__

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

-/**
- * 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)
-{
- int r;
-
- __asm__("bsfl %1,%0\n\t"
- "jnz 1f\n\t"
- "movl $-1,%0\n"
- "1:" : "=r" (r) : "rm" (x));
- return r+1;
-}
-
-/**
- * fls - find last bit set
- * @x: the word to search
- *
- * This is defined the same way as ffs().
- */
-static inline int fls(int x)
-{
- int r;
-
- __asm__("bsrl %1,%0\n\t"
- "jnz 1f\n\t"
- "movl $-1,%0\n"
- "1:" : "=r" (r) : "rm" (x));
- return r+1;
-}
-
#include <asm-generic/bitops/hweight.h>

#endif /* __KERNEL__ */
diff --git a/include/asm-x86/bitops_64.h b/include/asm-x86/bitops_64.h
index 87e1a17..866ed56 100644
--- a/include/asm-x86/bitops_64.h
+++ b/include/asm-x86/bitops_64.h
@@ -35,71 +35,11 @@ static inline void set_bit_string(unsigned long *bitmap, unsigned long i,
}
}

-/**
- * ffz - find first zero in word.
- * @word: The word to search
- *
- * Undefined if no zero exists, so code should check against ~0UL first.
- */
-static inline unsigned long ffz(unsigned long word)
-{
- __asm__("bsfq %1,%0"
- :"=r" (word)
- :"r" (~word));
- return word;
-}
-
-/**
- * __ffs - find first bit in word.
- * @word: The word to search
- *
- * Undefined if no bit exists, so code should check against 0 first.
- */
-static inline unsigned long __ffs(unsigned long word)
-{
- __asm__("bsfq %1,%0"
- :"=r" (word)
- :"rm" (word));
- return word;
-}
-
-/*
- * __fls: find last bit set.
- * @word: The word to search
- *
- * Undefined if no zero exists, so code should check against ~0UL first.
- */
-static inline unsigned long __fls(unsigned long word)
-{
- __asm__("bsrq %1,%0"
- :"=r" (word)
- :"rm" (word));
- return word;
-}
-
#ifdef __KERNEL__

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

/**
- * 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)
-{
- int r;
-
- __asm__("bsfl %1,%0\n\t"
- "cmovzl %2,%0"
- : "=r" (r) : "rm" (x), "r" (-1));
- return r+1;
-}
-
-/**
* fls64 - find last bit set in 64 bit word
* @x: the word to search
*
@@ -112,22 +52,6 @@ static inline int fls64(__u64 x)
return __fls(x) + 1;
}

-/**
- * fls - find last bit set
- * @x: the word to search
- *
- * This is defined the same way as ffs.
- */
-static inline int fls(int x)
-{
- int r;
-
- __asm__("bsrl %1,%0\n\t"
- "cmovzl %2,%0"
- : "=&r" (r) : "rm" (x), "rm" (-1));
- return r+1;
-}
-
#define ARCH_HAS_FAST_MULTIPLIER 1

#include <asm-generic/bitops/hweight.h>


\
 
 \ /
  Last update: 2008-03-14 21:41    [W:0.070 / U:14.980 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site