Re: speed up verifying UTF-8

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;
>>
>> That seems right, I'll try that and update the patch. (Forgot to attach
>> earlier anyway)
> 
> Ugh, actually that has the same issue as before. If one of the bytes is
> in one half is zero, but not in the other half, this fail to detect it.
> Sorry for the noise..

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

- Heikki