[Patch, Fortran] Rework of floating point number reading

Steve Kargl sgk@troutmask.apl.washington.edu
Tue Dec 30 18:21:00 GMT 2008

On Tue, Dec 30, 2008 at 06:31:08PM +0100, Daniel Kraft wrote:
> For anyone interested, I looked at glibc-2.4 (the one on my system) 's 
> implementation, which is in stdlib/strtod_l.c and around 1600 lines of 
> code; I would not want to include this one in gfortran, to be honest.
> The basic idea is to to the same as my patch does, but use a gmp natural 
> number for the *10+digit thing.  For the division, it uses a table of 
> powers of ten instead of pow and copied code from GMP because it states 
> that not a full multiprecision division is needed but instead only a few 
> digits.  So here's another suggestion: Do the calculation ourselves but 
> use GMP for it?  I think we could do a simple code, not that optimized 
> and special-case-handling as the one in glibc, but (hopefully) with the 
> same precision.  It seems (?) that strtod uses GMP anyway, so can we do 
> that, too, in libgfortran?  Or are there systems libgfortran is supposed 
> to work on even without GMP (there we could simply use floating-point 
> numbers and allow the loss of precision)?  I hesitated to do my 
> calculation with large integers in the first place because I feared slow 
> code; but if glibc does it, it can't be too bad, I guess.


You may want to check out how David Gay handles the conversion.
See g_fmt.c at http://www.netlib.org/fp/index.html


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