Messages in this thread | | | Date | Thu, 21 Jan 2021 12:34:41 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH 5/6] lib: add fast path for find_next_*_bit() |
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On Wed, Jan 20, 2021 at 04:06:29PM -0800, Yury Norov wrote: > Similarly to bitmap functions, find_next_*_bit() users will benefit > if we'll handle a case of bitmaps that fit into a single word. In the > very best case, the compiler may replace a function call with a > single ffs or ffz instruction.
> + if (small_const_nbits(size)) { > + unsigned long val; > + > + if (unlikely(offset >= size)) > + return size;
> + val = *addr & BITMAP_FIRST_WORD_MASK(offset) > + & BITMAP_LAST_WORD_MASK(size);
Seems like a new helper can be introduced (BITS or BITMAP namespace depending on the decision):
#define _OFFSET_SIZE_MASK(o,s) \ (BITMAP_FIRST_WORD_MASK(o) & BITMAP_LAST_WORD_MASK(s))
val = *addr & BITMAP_OFFSET_SIZE_MASK(offset, size);
And so on below.
> + return val ? __ffs(val) : size; > + }
-- With Best Regards, Andy Shevchenko
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