[GRASS-dev] scientific notation in r.mapcalc ?

[Glynn Clements]

Markus Neteler wrote:

> > I just stumbled upon this while running a large model, and noticed that I
> > couldn't easily find an answer:
> >
> > IIUC r.mapcalc does not support scientific notation of floating point
> > numbers (i.e. 2.540000e-05 instead of 0.0000254). Is that correct ?
> >
> > How difficult would it be to implement the support of such notation ?
> 
> We just stumbled over the same issue... would be nice to have.

It works here:

	$ r.mapcalc "foo = 2.540000e-05"
	$ r.info -r foo
	min=2.54e-05
	max=2.54e-05

        $ g.version -gr
        version=7.3.svn
        date=2016
        revision=r70088
        build_date=2017-06-16
        build_platform=x86_64-pc-linux-gnu
        build_off_t_size=8
        libgis_revision=70829 
        libgis_date="2017-04-04 08:43:02 +0100 (Tue, 04 Apr 2017) "

mapcalc.l specifically recognises exponential notation:

        I		[0-9]+
        
        E		[eE][-+]?[0-9]+
        
        %%
        
        {I}"."{I}?{E}?	|
        "."{I}{E}?	{
        			yylval.fval = atof(yytext);
        			return DOUBLE;
        		}

atof() is specified as:

       7.20.1.1  The atof function

	...

       [#2]  The  atof function converts the initial portion of the
       string pointed to by nptr to double representation.   Except
       for the behavior on error, it is equivalent to

               strtod(nptr, (char **)NULL)

and strtod() as

       7.20.1.3  The strtod, strtof, and strtold functions

	...

       [#3] The  expected  form  of  the  subject  sequence  is  an
       optional plus or minus sign, then one of the following:

         -- a   nonempty  sequence  of  decimal  digits  optionally
            containing a decimal-point character, then an  optional
            exponent part as defined in 6.4.4.2;

I note that any locale-specific varations are supposed to be in
addition to the format used by the "C" locale, so even if LC_NUMERIC
gets set (and it shouldn't), that shouldn't affect it.

Is this issue a wxGUI thing?

-- 
Glynn Clements <glynn at gclements.plus.com>