Re: BUG #17774: Assert triggered on brin_minmax_multi.c

> On Thu, Feb 09, 2023 at 05:18:47PM +0100, Tomas Vondra wrote:
>
> I believe the bug is pretty trivial - the code applies the netmask
> incorrectly, so that with 127.0.0.1/0 it ends with 0.0.0.1, and because
> it assumes 0.0.0.1 < 0.0.0.0 it ends with negative delta.
>
> In particular, the issue is that the code does this:
>
>     lena = ip_bits(ipa);     -- 0
>     len = ip_addrsize(ipa);  -- 4
>
>     for (for (i = 0; i < len; i++)
>     {
>       nbits = lena - (i * 8);
>       ...
>       mask = (0xFF << (8 - nbits));
>       ...
>     }
>
> But for 127.0.0.1/0 we get lena=0, so for i>0 nbits gets negative, and
> the shift is probably going to do something silly (not sure what
> exactly, but AFAICS it's undefined behavior).
>
> Attached is a fixup that resolves this failure for me. I need to look a
> bit closer if there are some other issues (e.g. with the float rounding
> errors, etc.).

Thanks, the fix looks good and solves the issue. With the patch applied
after a quick round of testing I haven't found any failures so far,
whether due to float arithmetic or something else.