[GRASS-dev] Overflow warning in r.mapcalc calculation

[Paulo van Breugel]

Thanks Markus,

That is certainly a good suggestion. The problem however remains I think 
with the part

round(C / 0.0001)

If C/0.0001 > 2^31, i.e., larger then the maximum possible integer, 
there will be an error.

The white spaces, is that for another reason then being clearer?

Cheers,

Paulo


On 05/17/2013 10:57 PM, Markus Metz wrote:
> On Fri, May 17, 2013 at 5:13 PM, Paulo van Breugel
> <p.vanbreugel at gmail.com> wrote:
>> Hi Glynn and Rainer
>>
>> Happy to see this exchange of ideas. It would be great if this could be
>> implemented. Do you think it is useful I make a feature request on the bug
>> tracker (with link to this email thread) so the idea doesn't get lost?
> Instead of
>
> r.mapcalc "A = if(B==0,
> (round(C/0.0001)-1175699902)/(3007966667-1175699902) *100.0, 1)"
> --overwrite
>
> try
>
> r.mapcalc "A = if(B==0,
> (round(C/0.0001)-1175699902.0)/(3007966667.0-1175699902.0) *100.0, 1)"
> --overwrite
>
> or better with whitespaces
>
> r.mapcalc "A = if(B == 0, (round(C / 0.0001) - 1175699902.0) /
> (3007966667.0 - 1175699902.0) * 100.0, 1)" --overwrite
>
> adding .0 to numbers forces all calculations to be done with  floating
> point double precision
>
> Markus M
>
>>
>>
>>
>> On Fri, May 17, 2013 at 4:38 PM, Glynn Clements <glynn at gclements.plus.com>
>> wrote:
>>>
>>> Rainer M. Krug wrote:
>>>
>>>>> One option is to modify round() to take a second argument (defaulting
>>>>> to 1), and have it return the first argument rounded to the nearest
>>>>> multiple of the second. The return type would be that of the second
>>>>> argument, i.e. round(x,1) rounds to the nearest integer and returns an
>>>>> integer, round(x,1.0) rounds to the nearest integer and returns a
>>>>> float, round(x,1e-3) would round to 3 decimal places (i.e. the nearest
>>>>> multiple of 0.001), etc.
>>>> Sounds like a sensible approach without adding to many new
>>>> functions. But I would actually split the two, i.e. have two more
>>>> arguments, where one specifies the type,
>>>> and the other one the number of decimals to round to, i.e.
>>>>
>>>> round(x, 0, "I") would be the default, rounding to whole number and
>>>> return an integer
>>> That interface isn't possible. r.mapcalc doesn't have a string type,
>>> and there's no way that a function's return type can depend upon the
>>> value of a parameter.
>>>
>>> --
>>> Glynn Clements <glynn at gclements.plus.com>
>>> _______________________________________________
>>> grass-dev mailing list
>>> grass-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-dev
>>
>>
>> _______________________________________________
>> grass-dev mailing list
>> grass-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-dev

-- 

Paulo van Breugel
Department of Geosciences and Natural Resource Management
Section of Forest, Nature and Biomass
University of Copenhagen

Rolighedsvej 23
1958 Frederiksberg C
Phone: +45 353-31646
Phone: +31 6 12189147
e-mail: pvb at life.ku.dk
e-mail: p.vanbreugel at gmail.com

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