Dominique Pelle wrote:
> >> After the patch, starting nerdtree in VIM's src is ~35% faster (1.7s vs
> >> 2.6s) and the CRT's locale handling functions no longer appear in the
> >> profile (and I warmed the file cache to remove disk reading from the
> >> times). In general this should help speed up longer running VIML scripts.
> >
> > Yeah, we've had problems with library functions before.
> >
> > I think using a table is often slower than simple compares, because a
> > table lookup has to access memory, while a compare is local inside the
> > CPU. Especially for ASCII_ISLOWER and ASCII_ISUPPER, it's just two
> > compares. Changing VIM_ISDIGIT() this way is likely to make it slower.
> > ASCII_ISALNUM() requires six compares, perhaps a table is faster then?
>
>
> You can half the number of comparisons when doing range checking.
> Instead of doing 2 comparisons...
>
> if (c >= '0' && c <= '9')
>
> You can do it in one comparison with this trick:
>
> if ((unsigned)c - '0' < 10)
>
> And that can be faster than tables lookup because table access
> thrashes the L1 cache.
Nice trick. Especially because "c" is only used once, thus side effects
are OK.
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