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Groups > comp.lang.c++ > #82817
| From | Bonita Montero <Bonita.Montero@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: Can anyone improve this ? |
| Date | 2022-01-18 09:18 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <ss5t4r$efe$1@dont-email.me> (permalink) |
| References | <srjdtm$d9c$1@dont-email.me> <86ee56rzbz.fsf@linuxsc.com> |
Am 17.01.2022 um 19:28 schrieb Tim Rentsch:
> Bonita Montero <Bonita.Montero@gmail.com> writes:
>
>> I had an idea how to write a fast UTF-8 strlen, here it is:
>>
>> size_t utf8Strlen( char const *str )
>> {
>> struct encode_t { size_t lenIncr, strIncr; };
>> static encode_t const encodes[] =
>> {
>> { 1, 1 },
>> { 0, 0 },
>> { 1, 2 },
>> { 1, 3 },
>> { 1, 4 },
>> { 0, 0 },
>> { 0, 0 },
>> { 0, 0 },
>> { 0, 0 }
>> };
>> size_t len = 0;
>> for( unsigned char c; (c = *str); )
>> {
>> encode_t const &enc =
>> encodes[(size_t)countl_zero<unsigned char>( ~c )];
>> if( !enc.lenIncr ) [[unlikely]]
>> return -1;
>> len += enc.lenIncr;
>> for( char const *cpEnd = str + enc.strIncr; ++str != cpEnd; )
>> if( ((unsigned char)*str & 0x0C0) != 0x080 ) [[unlikely]]
>> return -1;
>> }
>> return len;
>> }
>>
>> Has anyone further ideas to improve this ?
>
> Just for fun -
>
> size_t
> utf8_units_two( const char *s ){
> size_t r = -1;
> unsigned char c;
>
> next:
> switch( r++, c = *s++, c >> 3 ){
> cases(16,17,18,19,20,21,22,23,31): return -1;
>
> cases(30): if( c = *s++, c >> 6 != 2 ) return -1;
> cases(28,29): if( c = *s++, c >> 6 != 2 ) return -1;
> cases(24,25,26,27): if( c = *s++, c >> 6 != 2 ) return -1;
> cases(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15): goto next;
>
> cases(0): if( c != 0 ) goto next;
> }
>
> return r;
> }
That's not C or C++ and it does have a lot of branch-mispredictions.
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Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-11 09:08 +0100
Re: Can anyone improve this ? Juha Nieminen <nospam@thanks.invalid> - 2022-01-11 09:50 +0000
Re: Can anyone improve this ? Juha Nieminen <nospam@thanks.invalid> - 2022-01-11 11:07 +0000
Re: Can anyone improve this ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-11 11:08 +0000
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-11 18:28 +0100
Re: Can anyone improve this ? Christian Gollwitzer <auriocus@gmx.de> - 2022-01-11 18:41 +0100
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-11 19:36 +0100
Re: Can anyone improve this ? Öö Tiib <ootiib@hot.ee> - 2022-01-11 21:54 -0800
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-11 21:51 +0100
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-12 14:19 +0100
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-12 14:20 +0100
Re: Can anyone improve this ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-12 14:14 +0000
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-12 17:20 +0100
Re: Can anyone improve this ? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-01-12 08:38 -0800
Re: Can anyone improve this ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-01-12 16:55 +0000
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-16 12:09 -0800
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-16 12:12 -0800
Re: Can anyone improve this ? Öö Tiib <ootiib@hot.ee> - 2022-01-16 13:00 -0800
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 10:13 -0800
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 10:28 -0800
Re: Can anyone improve this ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-01-17 21:51 +0100
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 16:16 -0800
Re: Can anyone improve this ? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-17 22:43 -0800
Re: Can anyone improve this ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-01-18 12:09 +0100
Re: Can anyone improve this ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-18 09:18 +0100
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