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

[Wei Wang]

On 12/14/2017 11:47 AM, Wei Wang wrote:
> On 12/13/2017 10:16 PM, Tetsuo Handa wrote:
>
>
> > >                           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_start;
> > >                   } else if (bitmap) {
> > >                           if (set)
> > >                                   ret = find_next_bit(bitmap->bitmap,
> > > IDA_BITMAP_BITS, bit);
> > >                           else
> > >                                   ret = 
> > > find_next_zero_bit(bitmap->bitmap,
> > > IDA_BITMAP_BITS, bit);
> > "bit" may not be 0 for the first round and "bit" is always 0 afterwords.
> > But where is the guaranteed that "end" is a multiple of 
> > IDA_BITMAP_BITS ?
> > Please explain why it is correct to use IDA_BITMAP_BITS unconditionally
> > for the last round.
>
> There missed something here, it will be:
>
> nbits = min(end - ida_start + 1, IDA_BITMAP_BITS - bit);


captured a bug here, should be:
nbits = min(end - ida_start + 1, (unsigned long)IDA_BITMAP_BITS);


> if (set)
>     ret = find_next_bit(bitmap->bitmap, nbits, bit);
> else
>     ret = find_next_zero_bit(bitmap->bitmap,
>                                            nbits, bit);
> if (ret < nbits)
>     return ret + ida_start;

Best,
Wei