Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!ncar!gatech!psuvax1!psuvm.bitnet!uh2
From: UH2@PSUVM.BITNET (Lee Sailer)
Newsgroups: comp.sys.amiga.tech
Subject: C question
Message-ID: <56733UH2@PSUVM>
Date: 10 Oct 88 18:46:58 GMT
Organization: Penn State Erie, Behrend College
Lines: 33

I have stumbled onto one of those C mystery problems, using Lattice 4.01.

INT_MAX is a #define for the largest int.  In my code I have

     r1 = 1.0/(double)INT_MAX

and

     double im = INT_MAX;
     r2 = 1.0/im;

Guess what?  r1 and r2 get different values.  How come?

This only occurs with FFP.  I know it isn't as accurate ,but I didn't
expect it to be crazy.
                                                              lee

#include <limits.h>
#include <stdio.h>

main()
{
        double r1, r2, r3,  im=INT_MAX;
        int iim = INT_MAX;

        r1 = 1.0/(double)INT_MAX;
        r2 = 1.0/im;
        r3 = 1.0/(double)iim;

        printf("r1 == %g, r2 ==  %g, r3 == %g.\n", r1, r2, r3);
        return 0;
}

With FFP, r1 == r2 != r3.  With IEEE, they are equal, and have a
differnt value from either with FFP.