Messages in this thread | | | Date | Fri, 14 Mar 2008 16:30:37 -0700 | From | Randy Dunlap <> | Subject | Re: [PATCH v2] x86: merge the simple bitops and move them to bitops.h |
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On Fri, 14 Mar 2008 21:35:26 +0100 Alexander van Heukelum wrote:
> x86: merge the simple bitops and move them to bitops.h. > > > Improved comments for ffs and fls.
There is still room for some comment improvements IMO. See below.
> Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm> > > --- > > diff --git a/include/asm-x86/bitops.h b/include/asm-x86/bitops.h > index 1a23ce1..363a4ff 100644 > --- a/include/asm-x86/bitops.h > +++ b/include/asm-x86/bitops.h > @@ -310,6 +309,104 @@ static int test_bit(int nr, const volatile unsigned long *addr); > constant_test_bit((nr),(addr)) : \ > variable_test_bit((nr),(addr))) > > +/** > + * __ffs - find first bit in word.
find first bit set in word
[The "first bit in word" could have any value in {0, 1}, so the return value would depend on which end you considered "first". ;]
> + * @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__("bsf %1,%0" > + :"=r" (word) > + :"rm" (word)); > + return word; > +} > + > +/** > + * ffz - find first zero in word.
find first zero bit in word
> + * @word: The word to search > + * > + * Undefined if no zero exists, so code should check against ~0UL first. > + */ > +static inline unsigned long ffz(unsigned long word) > +{ > + __asm__("bsf %1,%0" > + :"=r" (word) > + :"r" (~word)); > + return word; > +} > + > +/* > + * __fls: find last bit set.
__fls - find last bit set in word
> + * @word: The word to search > + * > + * Undefined if no zero exists, so code should check against ~0UL first. > + */ > +static inline unsigned long __fls(unsigned long word) > +{ > + __asm__("bsr %1,%0" > + :"=r" (word) > + :"rm" (word)); > + return word; > +} > + > +#ifdef __KERNEL__ > +/** > + * ffs - find first bit set
in word
> + * @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 other bitops. > + * > + * ffs(value) returns 0 if value is 0 or the position of the first > + * set bit if value is nonzero. The first (least significant) bit > + * is at position 1. > + */ > +static inline int ffs(int x) > +{ > + int r; > +#ifdef CONFIG_X86_CMOV > + __asm__("bsfl %1,%0\n\t" > + "cmovzl %2,%0" > + : "=r" (r) : "rm" (x), "r" (-1)); > +#else > + __asm__("bsfl %1,%0\n\t" > + "jnz 1f\n\t" > + "movl $-1,%0\n" > + "1:" : "=r" (r) : "rm" (x)); > +#endif > + return r + 1; > +} > + > +/** > + * fls - find last bit set
in word
> + * @x: the word to search > + * > + * This is defined in a similar way as the libc and compiler builtin > + * ffs, but returns the position of the most significant set bit. > + * > + * fls(value) returns 0 if value is 0 or the position of the last > + * set bit if value is nonzero. The last (most significant) bit is > + * at position 32. > + */ > +static inline int fls(int x) > +{ > + int r; > +#ifdef CONFIG_X86_CMOV > + __asm__("bsrl %1,%0\n\t" > + "cmovzl %2,%0" > + : "=&r" (r) : "rm" (x), "rm" (-1)); > +#else > + __asm__("bsrl %1,%0\n\t" > + "jnz 1f\n\t" > + "movl $-1,%0\n" > + "1:" : "=r" (r) : "rm" (x)); > +#endif > + return r + 1; > +} > +#endif /* __KERNEL__ */
--- ~Randy
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