Path: utzoo!attcan!uunet!wuarchive!emory!mephisto!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!csc!csc3.anu.oz!neptune!peterf
From: peterf@arp.anu.oz.au (Peter Fletcher)
Newsgroups: comp.sys.apollo
Subject: Casting bug in C compiler 68K Rev 6.7(316)
Message-ID: <1990Jul17.044917.20375@arp.anu.oz.au>
Date: 17 Jul 90 04:49:17 GMT
Organization: Automated Reasoning Project, ANU, Australia
Lines: 34

There's a frustrating little bug in the Apollo 'c' compiler
which has been there since at least before Rev 6.6.  The
following program should always output '65535', but if
compiled with no optimization, it gets the answer wrong.

>hera$ rm cbug ; make CC=/bin/cc cbug
>/bin/cc     cbug.c   -o cbug
>hera$ cbug
>65280
>hera$ rm cbug ; make CC=/bin/cc CFLAGS=-O cbug
>/bin/cc -O    cbug.c   -o cbug
>hera$ cbug
>65535
>hera$ cat cbug.c
>main()
>
>{
>    unsigned short a;
>    int off;
>    float scale;
>    unsigned short result;
>
>    a = 0;
>    off = -1;
>    scale = 1.0;
>
>    result = ((unsigned short)(((a)+off)*scale));
>
>    printf("%1u\n",result);
>}
>hera$ /com/cc -version
>C compiler 68K Rev 6.7(316)

peter fletcher