Re: [Win32, C, and way OT] C floats, doubles, and their equivalence


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Re: [Win32, C, and way OT] C floats, doubles, and their equivalence

by creamygoodness (Curate)

on Jul 18, 2009 at 16:32 UTC ( #781353=note: print w/replies, xml )

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in reply to [Win32, C, and way OT] C floats, doubles, and their equivalence

Seems like the conversion glitch could be happening at several places.

Maybe the initial assignment of float foo needs a cast. MSVC warns about loss of precision in such cases -- maybe it's serious. :)

float foo = (float)nv;
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As a workaround, perhaps you could truncate the initial assignment of the double:

double nv = (float)(2.0 / 3);
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Lastly, maybe something is awry in the conversions that are being done during the comparison -- like it's ignoring your cast. It's a stab in the dark, but maybe a hack like this would get it to pay attention:

static __inline int
compare_truncated_double_to_float(double d, float f)
{
    float truncted_double = (float)d;
    if (f == truncated_double) { return 1; }
    else                       { return 0; }
}
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PS: This is relevant to the work I do ensuring Windows compatibility for my XS distros.

--
Marvin Humphrey

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Re^2: [Win32, C, and way OT] C floats, doubles, and their equivalence
by syphilis (Archbishop) on Jul 19, 2009 at 00:12 UTC

It's a stab in the dark ...

#include <stdio.h>

int main(void) {

   double nv = 2.0 / 3;
   float foo = 2.0 / 3;
   float truncated = (float)nv;

   if(foo == truncated) printf("True ");
   else printf("False ");

   if(foo == (float)nv) printf("True\n");
   else printf("False\n");

   return 0;
}
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PS: This is relevant to the work I do ensuring Windows compatibility for my XS distros

#if defined _MSC_VER && _MSC_VER < 1400

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