Messages in this thread |  | | Date | Tue, 2 Oct 2018 11:21:42 +0300 | From | Andy Shevchenko <> | Subject | Re: [RESEND PATCH v4 1/8] bitops: Introduce the for_each_set_clump macro |
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On Tue, Oct 02, 2018 at 09:42:48AM +0200, Rasmus Villemoes wrote: > On 2018-10-02 03:13, William Breathitt Gray wrote:
> The cover letter says > > The clump_size argument can be an arbitrary number of bits and is not > required to be a multiple of 2. > > by which I assume you mean "power of 2", but either way, the above code > does not seem to take into account the case where bits_offset + > clump_size straddles a word boundary, so it wouldn't work for a > clump_size that does not divide BITS_PER_LONG.
E.g. 3 bits in a clump? Hmm...
Why would we need that? I mean some real use case?
> May I suggest another approach:
You may, of course, but see above and my comments below.
> unsigned long bitmap_get_value(const unsigned long *bitmap, unsigned > start, unsigned width): Get the value of bitmap[start:start+width] for > 1<=width<=BITS_PER_LONG (it's up to the caller to ensure this is within > the defined region). That can almost be an inline > > bitmap_get_value(const unsigned long *bitmap, unsigned start, unsigned > width) > { > unsigned idx = BIT_WORD(start); > unsigned offset = start % BITS_PER_LONG; > unsigned long lower = bitmap[idx] >> offset; > unsigned long upper = offset <= BITS_PER_LONG - width ? 0 : > bitmap[idx+1] << (BITS_PER_LONG - offset); > return (lower | upper) & GENMASK(width-1, 0) > } > > Then you can implement the for_each_set_clump by a (IMO) more readable > > for (i = 0, start = 0; i < num_ports; i++, start += gpio_reg_size) { > word_mask = bitmap_get_value(mask, start, gpio_reg_size); > if (!word_mask) > continue; > ... > }
I would rather go with two prototypes to get()/set() a clump in the bitmap in a way when it's aligned and BITS_PER_LONG % clump_size == 0.
unsigned long bitmap_get_clump(unsigned long *src, unsigned int start, unsigned int clump_size) { unsigned int index = BIT_WORD(start); unsigned int offset = start % BITS_PER_LONG;
/* These just for spelling the restrictions */ WARN_ON(BITS_PER_LONG % clump_size); WARN_ON(offset % clump_size);
/* TODO: take care of clump_size == 64 */ return (bitmap[index] >> offset) & GENMASK(clump_size - 1, 0); }
Something similar with set with additional parameter unsigned long value which has MSB cleared till we reach [clump_size - 1 : 0].
-- With Best Regards, Andy Shevchenko
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