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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_ */ |
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