Re: speed up verifying UTF-8

On Thu, Jun 3, 2021 at 3:22 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>
> On 03/06/2021 22:16, Heikki Linnakangas wrote:
> > On 03/06/2021 22:10, John Naylor wrote:
> >> On Thu, Jun 3, 2021 at 3:08 PM Heikki Linnakangas <hlinnaka@iki.fi
> >> <mailto:hlinnaka@iki.fi>> wrote:
> >>   >                 x1 = half1 + UINT64CONST(0x7f7f7f7f7f7f7f7f);
> >>   >                 x2 = half2 + UINT64CONST(0x7f7f7f7f7f7f7f7f);
> >>   >
> >>   >                 /* then check that the high bit is set in each byte. */
> >>   >                 x = (x1 | x2);
> >>   >                 x &= UINT64CONST(0x8080808080808080);
> >>   >                 if (x != UINT64CONST(0x8080808080808080))
> >>   >                         return 0;

> If you replace (x1 | x2) with (x1 & x2) above, I think it's correct.

After looking at it again with fresh eyes, I agree this is correct. I modified the regression tests to pad the input bytes with ascii so that the code path that works on 16-bytes at a time is tested. I use both UTF-8 input tables for some of the additional tests. There is a de facto requirement that the descriptions are unique across both of the input tables. That could be done more elegantly, but I wanted to keep things simple for now.