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Commit cd85c8b4 authored by Steven Rostedt's avatar Steven Rostedt Committed by Linus Torvalds
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[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: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 79a88102

include/asm-i386/bitops.h

+24 −30
Original line number Diff line number Diff line
@@ -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.

 */