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[PATCH] speed up on find_first_bit for i386 (let compiler do the work)

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Avoid using "rep scas", just let the compiler select a sequence of
regular instructions.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Steven Rostedt 2005-07-28 08:45:06 -04:00 committed by Linus Torvalds
parent 79a8810221
commit cd85c8b445
1 changed files with 24 additions and 30 deletions
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54
include/asm-i386/bitops.h
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@ -310,6 +310,20 @@ static inline int find_first_zero_bit(const unsigned long *addr, unsigned size)
*/
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
@ -320,22 +334,16 @@ int find_next_zero_bit(const unsigned long *addr, int size, int offset);
*/
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 long 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__("bsfl %1,%0"
:"=r" (word)
:"rm" (word));
return word;
}
/*
* fls: find last bit set.
*/