[patch] Fix PR libfortran/95177, ctype.h functions should not be called with char arguments

[Thomas Koenig]

On 17.12.21 00:34, FX via Fortran wrote:
>> unrelated PS: I’ve been thinking aloud and benchmarking faster integer I/O for libgfortran at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98076
>> Comments are welcome on the proposed design, I think the current proposal is a low-hanging fruit (not risky, much faster).
> 
> Quick test integrating the idea into libgfortran, here are the timings to make a formatted write of 10 million integers into a string:
> 
> - very small value (1), negligible speedup (2.273s to 2.248s)
> - small value (1042), speedup of 28% (3.224s to 2.350s)
> - huge(0_8), speed up of 50% (5.914s to 2.560s)
> - huge(0_16), speed up of 83% (19.46s to 3.31s)
> 
> Conclusion: this looks quite interesting!

Yes indeed.
> I’m not sure what use cases people have for writing lots of formatted integers, but this doesn’t sound too bad.

If there is an obvoius speed-up to be had, we should go for it, for
a) the coolness value and
b) because somebody might need it :-)

> 
> Further thought: fast 64-bit itoa() implementations, under the MIT license (https://github.com/jeaiii/itoa) promise a speed-up of 2 to 10 times compared to naive implementation. That could bring us down further, but we probably cannot incorporate that, right?

Not sure about that.  We could reverse-engineer the algorithm,
if necessary (and if we are convinced that it is mathematically
correct :-)

> 
> Two questions:
> 
> 1. This is easy, am I missing something? Some reason why it was never tried before?

Round tuits seem to have been lacking :-)

> 2. Why is gfc_xtoa() in runtime/error.c? We should probably move it.

No idea, and yes.