[virtio-dev] Re: [PATCH v19 3/7] xbitmap: add more operations

[Wei Wang <wei.w.wang@intel.com>]

On 12/15/2017 12:29 AM, Tetsuo Handa wrote:
> Wei Wang wrote:
>> I used the example of xb_clear_bit_range(), and xb_find_next_bit() is
>> the same fundamentally. Please let me know if anywhere still looks fuzzy.
> I don't think it is the same for xb_find_next_bit() with set == 0.
>
> +		if (radix_tree_exception(bmap)) {
> +			unsigned long tmp = (unsigned long)bmap;
> +			unsigned long ebit = bit + 2;
> +
> +			if (ebit >= BITS_PER_LONG)
> +				continue;
> +			if (set)
> +				ret = find_next_bit(&tmp, BITS_PER_LONG, ebit);
> +			else
> +				ret = find_next_zero_bit(&tmp, BITS_PER_LONG,
> +							 ebit);
> +			if (ret < BITS_PER_LONG)
> +				return ret - 2 + IDA_BITMAP_BITS * index;
>
> What I'm saying is that find_next_zero_bit() will not be called if you do
> "if (ebit >= BITS_PER_LONG) continue;" before calling find_next_zero_bit().
>
> When scanning "0000000000000000000000000000000000000000000000000000000000000001",
> "bit < BITS_PER_LONG - 2" case finds "0" in this word but
> "bit >= BITS_PER_LONG - 2" case finds "0" in next word or segment.
>
> I can't understand why this is correct behavior. It is too much puzzling.
>

OK, I'll post out a version without the exceptional path.

Best,
Wei


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