cast(int) getting an unexpected number

Lars T. Kyllingstad public at kyllingen.NOSPAMnet
Wed Nov 4 09:04:48 PST 2009


Michal Minich wrote:
> Hello rmcguire,
> 
>> why is this not a compiler bug?
>> because:
>> import std.stdio;
>> void main() {
>> float f=0.01;
>> writefln("%0.2f->%d",f,cast(int)(f*100f));
>> writefln("%0.2f->%d",f,cast(int)(.01*100f));
>> writefln("%0.2f->%f",f,(f*100f));
>> }
>> results in:
>> 0.01->0
>> 0.01->1
>> 0.01->1.000000
>> I would say something is dodgy.
>>
>> -Rory
>>
> 
> I think this may be case of:
> At comple time floating point computations may be done at a higher 
> precision than run time.


Yes, if you do this:

   float f = 0.01;
   float g = f * 100f;
   real r  = f * 100f;
   writeln("%s, %s, %s", f, cast(int) g, cast(int) r);

you get:

   0.01, 0, 1

I believe just writing cast(int)(f*100f) is more or less the same as the 
'real' case above.

-Lars


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