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SubjectRe: [PATCH v4 0/8] Introduce the for_each_set_clump macro
On Wed, May 16, 2018 at 5:03 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Tue, May 15, 2018 at 6:22 PM, William Breathitt Gray
> <vilhelm.gray@gmail.com> wrote:
>
>> For example, suppose you would like to iterate over a 16-bit integer 4
>> bits at a time, skipping over 4-bit groups with no set bit, where XXXX
>> represents the current 4-bit group:
>>
>> Example: 1011 1110 0000 1111
>> First loop: 1011 1110 0000 XXXX
>> Second loop: 1011 XXXX 0000 1111
>> Third loop: XXXX 1110 0000 1111
>>
>> Each iteration of the loop returns the next 4-bit group that has at
>> least one set bit.
>>
>> The for_each_set_clump macro has six parameters:
>>
>> * clump: set to current clump index for the iteration
>> * index: set to current bitmap word index for the iteration
>> * offset: bits offset of the found clump in the bitmap word
>> * bits: bitmap to search within
>> * size: bitmap size in number of clumps
>> * clump_size: clump size in number of bits
>>
>> The clump_size argument can be an arbitrary number of bits and is not
>> required to be a multiple of 2.
>
> I must say I'm impressed. Very nice arithmetics going on there.
>
> If I can get some ACK for the bitops patch I'd be happy to merge
> it all through the GPIO tree. The users are pretty clear cut.

Give me also some time to go through proposed API, I think it might
have needed more alignment with existing find_* and for_* helpers.

> BTW: if I could, I would pull out Donald Knuth's "The Art of Computer
> Programming vol 4A" chapter 7.1.3 "Bitwise Tricks and Techniques"
> to see what he has to say about the subject, but I don't have
> that book as it turns out.

I can also add the Standford collection of bit algos here:

https://graphics.stanford.edu/~seander/bithacks.html

--
With Best Regards,
Andy Shevchenko

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