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Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!ihnp4!stolaf!umn-cs!digi-g!mark
From: mark@digi-g.UUCP (Mark Mendel)
Newsgroups: net.bugs,net.sources
Subject: bug in some 68000 C-compilers
Message-ID: <228@digi-g.UUCP>
Date: Tue, 11-Sep-84 11:57:33 EDT
Article-I.D.: digi-g.228
Posted: Tue Sep 11 11:57:33 1984
Date-Received: Fri, 14-Sep-84 20:52:56 EDT
Organization: DigiGraphic Systems Corp., Mpls.  MN
Lines: 37

I have discovered a bug in our C compiler (Pixel Computer Inc., Version 1.2,
3/9/84).  Since this bug caused a core dump in the net.sources game PHANTASIA
and many people have been CLUTTERING that group with complaints about a core
dump, I am guessing that this bug is more wide spread.  I believe our compiler
is of Unisoft derivation.

Attached is a short program to determine if you suffer from the bug.

The bug is:  fcmp(), the compiler's floating point comparison routine, destroys
regiser d0.  This is only a problem if a floating comparison is used as PART of
an expression: previously computed sub-expressions are trashed. 
[in PHANTASIA, the routine printloc() uses such an expression as an array 
subscipt, which caused a core dump].

The fix (if you can't fix the compiler):  given an expressions like:

    ...+(x>1.0)+...

where x is a floating point variable, replace it with:

    tmpint = (x>1.0); ...+ tmpint + ...

===================== cut here =====================
#include <stdio.h>

main()
{
    double x = 1.0, y = 1.0;
    int i;

    i = (x > 0) + 2*(y>0);
    printf ("%d\n", i);
    if (i != 3)
	printf("your compiler has problems.\n");
}