[libvirt] [PATCH 2/4] fixup? util: Optimize virBitmapUnion()

[Ján Tomko]

On Mon, Jun 03, 2019 at 05:04:51PM +0200, Andrea Bolognani wrote:
>On Mon, 2019-06-03 at 16:43 +0200, Ján Tomko wrote:
>> On Mon, Jun 03, 2019 at 04:31:51PM +0200, Andrea Bolognani wrote:
>> > On Mon, 2019-06-03 at 14:10 +0200, Ján Tomko wrote:
>> > > if (b->nbits &&
>> > >     a->nbits < b->nbits &&
>> > >     virBitmapExpand(a, b->nbits -1) < 0) {
>> >
>> > Yeah, you're right, we need to account for the zero-indexing of bits.
>> > I mean, it's not like the resulting bitmap would be incorrect either
>> > way, but we might end up allocating more memory than it's actually
>> > required.
>>
>> Actually I do think it would be incorrect. The bitmap size is as
>> important as its values - e.g. if the resulting bitmap had 4 set bits,
>> a size of 4 vs 5 would alter the result of virBitmapIsAllSet.
>
>Oh, right, that's something that I hadn't considered. This is pretty
>much exactly why I didn't trust my implementation to be correct O:-)
>
>> > The first check seems unnecessary, though: the only case in which the
>> > argument to virBitmapExpand() would be incorrect is b->nbits == 0,
>> > but we know that both a->nbits and b->nbits are >= 0 and we also just
>> > verified that a->nbits < b->nbits, so b->nbits must be >= 1 and the
>> > argument to virBitmapExpand() will always be correct. Or am I missing
>> > something?
>>
>> Right, it will work unless someone changes nbits from size_t to double.
>
>So ACK to drop the first check while adopting your version of that
>hunk?
>

ACK indeed.

Or you can choose to apply my R-b tags, unlike someone ;)

Jano
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