linux-kernel - Re: [PATCH v4 0/8] Introduce the for_each_set

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Date:   Wed, 16 May 2018 23:08:28 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     William Breathitt Gray <vilhelm.gray@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/8] Introduce the for_each_set_clump macro

On Wed, May 16, 2018 at 5:03 PM, Linus Walleij <linus.walleij@...aro.org> wrote:
> On Tue, May 15, 2018 at 6:22 PM, William Breathitt Gray
> <vilhelm.gray@...il.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