Messages in this thread | | | Date | Fri, 20 Nov 2015 09:52:29 +0100 | Subject | Re: [PATCH 2/3] lib: Introduce 2 find bit api: all_is_bit_{one,zero} | From | Geert Uytterhoeven <> |
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On Thu, Nov 19, 2015 at 3:31 AM, Jia He <hejianet@gmail.com> wrote: > --- a/lib/find_bit.c > +++ b/lib/find_bit.c > @@ -131,6 +131,56 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size) > EXPORT_SYMBOL(find_last_bit); > #endif > > +#ifndef all_bit_is_zero > +/* > + * return val: 1 means all bit is zero > + */ > +unsigned int all_bit_is_zero(const unsigned long *addr, unsigned size) > +{ > + unsigned long idx; > + unsigned long mask = size; > + > + if (unlikely(size == 0)) > + return 1; > + > + if (size > BITS_PER_LONG) { > + for (idx = 0; idx * BITS_PER_LONG < size; idx++)
Please move the multiplication (yes, a shift) out of the loop. Not all CPUs have barrel shifters.
> + if (addr[idx]) > + return 0; > + > + mask = size - (idx - 1) * BITS_PER_LONG; > + } > + > + return !(*addr & BITMAP_LAST_WORD_MASK(mask)); > +} > +EXPORT_SYMBOL(all_bit_is_zero);
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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