Re: Fun with floating point

[Meta via Digitalmars-d-learn]

On Saturday, 7 February 2015 at 16:06:14 UTC, Kenny wrote:
Hi, D community!
I have this program:

import std.stdio;
import std.conv;

int main(string[] argv)
{
      float eps = 1.0f;
      float f = 0.0f;
      while (f + eps != f)
          f += 1.0f;

      writeln("eps = " ~ to!string(eps) ~ ", max_f = " ~
to!string(f));
      return 0;
}

According to the languge specification what result would you
expect from its execution?

When running similar C++ program (VS 2013) the loop terminates
and I get t = 2^24 = 16777216.

Does D language specifies that loop will be terminated for this
program or  ?

I compiled with DMD and it hungs.
Details about assembly generated by DMD can be found here:
http://stackoverflow.com/questions/28380651/floating-point-maxing-out-loop-doesnt-terminate-in-d-works-in-c

Thanks.

A point of advice that Walter gives for situations like these is 
to ensure that your algorithm has a minimum required precision to 
work correctly but not a maximum. As Peter Alexander mentioned, 
DMD performs intermediate calculations at higher precision than 
GDC/LDC and thus your algorithm breaks.