百度空间 | 百度首页 
 
查看文章
 
ffs/fls
2009-10-19 15:36
#if __LINUX_ARM_ARCH__ < 5

#include <asm-generic/bitops/ffz.h>
#include <asm-generic/bitops/__fls.h>
#include <asm-generic/bitops/__ffs.h>
#include <asm-generic/bitops/fls.h>
#include <asm-generic/bitops/ffs.h>

#else

static inline int constant_fls(int x)
{
int r = 32;

if (!x)
return 0;
if (!(x & 0xffff0000u)) {
x <<= 16;
r -= 16;
}
if (!(x & 0xff000000u)) {
x <<= 8;
r -= 8;
}
if (!(x & 0xf0000000u)) {
x <<= 4;
r -= 4;
}
if (!(x & 0xc0000000u)) {
x <<= 2;
r -= 2;
}
if (!(x & 0x80000000u)) {
x <<= 1;
r -= 1;
}
return r;
}

/*
* On ARMv5 and above those functions can be implemented around
* the clz instruction for much better code efficiency.
*/

static inline int fls(int x)
{
int ret;

if (__builtin_constant_p(x))
return constant_fls(x);

asm("clz\t%0, %1" : "=r" (ret) : "r" (x) : "cc");
ret = 32 - ret;
return ret;
}

#define __fls(x) (fls(x) - 1)
#define ffs(x) ({ unsigned long __t = (x); fls(__t & -__t); })
#define __ffs(x) (ffs(x) - 1)
#define ffz(x) __ffs( ~(x) )

#endif


#ifndef _ASM_GENERIC_BITOPS_FFS_H_
#define _ASM_GENERIC_BITOPS_FFS_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 = 1;

if (!x)
return 0;
if (!(x & 0xffff)) {
x >>= 16;
r += 16;
}
if (!(x & 0xff)) {
x >>= 8;
r += 8;
}
if (!(x & 0xf)) {
x >>= 4;
r += 4;
}
if (!(x & 3)) {
x >>= 2;
r += 2;
}
if (!(x & 1)) {
x >>= 1;
r += 1;
}
return r;
}

#endif /* _ASM_GENERIC_BITOPS_FFS_H_ */


类别:c语言实践 | 添加到搜藏 | 浏览() | 评论 (0)
 
最近读者:
 
网友评论:
发表评论:
姓 名:
网址或邮箱: (选填)
内 容:
验证码: 请点击后输入四位验证码,字母不区分大小写
      

     

©2009 Baidu