tree 58b294ef3cd90f08fa77555352de63934a881405
parent 79a8810221ee9ea96c4e5a5817afb88f22ea698c
author Steven Rostedt <[EMAIL PROTECTED]> Thu, 28 Jul 2005 16:45:06 -0400
committer Linus Torvalds <[EMAIL PROTECTED]> Thu, 28 Jul 2005 22:40:31 -0700
[PATCH] speed up on find_first_bit for i386 (let compiler do the work)
Avoid using "rep scas", just let the compiler select a sequence of
regular instructions.
Signed-off-by: Steven Rostedt <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
include/asm-i386/bitops.h | 54 ++++++++++++++++++++--------------------------
1 files changed, 24 insertions(+), 30 deletions(-)
diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
--- a/include/asm-i386/bitops.h
+++ b/include/asm-i386/bitops.h
@@ -311,6 +311,20 @@ static inline int find_first_zero_bit(co
int find_next_zero_bit(const unsigned long *addr, int size, int offset);
/**
+ * __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
@@ -320,22 +334,16 @@ int find_next_zero_bit(const unsigned lo
*/
static inline int find_first_bit(const unsigned long *addr, unsigned size)
{
- int d0, d1;
- int res;
-
- /* This looks at memory. Mark it volatile to tell gcc not to move it
around */
- __asm__ __volatile__(
- "xorl %%eax,%%eax\n\t"
- "repe; scasl\n\t"
- "jz 1f\n\t"
- "leal -4(%%edi),%%edi\n\t"
- "bsfl (%%edi),%%eax\n"
- "1:\tsubl %%ebx,%%edi\n\t"
- "shll $3,%%edi\n\t"
- "addl %%edi,%%eax"
- :"=a" (res), "=&c" (d0), "=&D" (d1)
- :"1" ((size + 31) >> 5), "2" (addr), "b" (addr) : "memory");
- return res;
+ int x = 0;
+ do {
+ if (*addr)
+ return __ffs(*addr) + x;
+ addr++;
+ if (x >= size)
+ break;
+ x += (sizeof(*addr)<<3);
+ } while (1);
+ return x;
}
/**
@@ -360,20 +368,6 @@ static inline unsigned long ffz(unsigned
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__("bsfl %1,%0"
- :"=r" (word)
- :"rm" (word));
- return word;
-}
-
/*
* fls: find last bit set.
*/
-
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