Messages in this thread | | | Date | Fri, 22 Mar 2019 20:22:44 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v10 01/10] bitops: Introduce the for_each_set_clump8 macro |
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On Thu, Mar 14, 2019 at 09:30:02PM +0900, William Breathitt Gray wrote: > This macro iterates for each 8-bit group of bits (clump) with set bits, > within a bitmap memory region. For each iteration, "start" is set to the > bit offset of the found clump, while the respective clump value is > stored to the location pointed by "clump". Additionally, the > bitmap_get_value8 and bitmap_set_value8 functions are introduced to > respectively get and set an 8-bit value in a bitmap memory region.
> +void bitmap_set_value8(unsigned long *const bitmap, const unsigned int size, > + const unsigned long value, const unsigned int start) > +{ > + const size_t index = BIT_WORD(start); > + const unsigned int offset = start % BITS_PER_LONG; > + const unsigned int low_width = (offset + 8 > BITS_PER_LONG) ? > + BITS_PER_LONG - offset : 8;
> + const unsigned long low_mask = GENMASK(offset + low_width - 1, offset);
I think
unsigned long low_mask = GENMASK(low_width - 1, 0) << offset;
will generate better code.
> + const unsigned int high_width = 8 - low_width; > + const unsigned long high_mask = GENMASK(high_width - 1, 0); > + > + /* set lower portion */ > + bitmap[index] &= ~low_mask; > + bitmap[index] |= value << offset; > + > + /* set higher portion if space available in bitmap */ > + if (high_width && start + 8 <= size) { > + bitmap[index + 1] &= ~high_mask; > + bitmap[index + 1] |= value >> low_width; > + } > +} > +EXPORT_SYMBOL(bitmap_set_value8);
-- With Best Regards, Andy Shevchenko
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