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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); 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 * find_first_bit - find the first set bit in a memory region
* @addr: The address to start the search at * @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) static inline int find_first_bit(const unsigned long *addr, unsigned size)
{ {
int d0, d1; int x = 0;
int res; do {
if (*addr)
/* This looks at memory. Mark it volatile to tell gcc not to move it around */ return __ffs(*addr) + x;
__asm__ __volatile__( addr++;
"xorl %%eax,%%eax\n\t" if (x >= size)
"repe; scasl\n\t" break;
"jz 1f\n\t" x += (sizeof(*addr)<<3);
"leal -4(%%edi),%%edi\n\t" } while (1);
"bsfl (%%edi),%%eax\n" return x;
"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;
} }
/** /**
@@ -360,20 +368,6 @@ static inline unsigned long ffz(unsigned long word)
return 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. * fls: find last bit set.
*/ */