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From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.lang.c
Subject: int divided by unsigned.
Message-ID: <13940@lanl.gov>
Date: 15 Jun 89 23:47:31 GMT
Distribution: na
Organization: Los Alamos National Laboratory
Lines: 23


#include "stdio.h"
main(){
   int a;
   unsigned b;

   a= -5;
   b=1000;
   printf("%d\n",a/=b);
}

I tried the above program on my sun workstation and it printed 4294967.
This is aparently the "correct" answer according to the proposed C
standard.  On the Cray under UNICOS, the same program prints 0.  The
"correct" answer for the Cray would have been 18446744073709551.  This
is an example of a case where deviating from the C definition produces
desireable results.  I hope Cray doesn't "fix" their C compiler.

(Note: this behaviour occurs because C requires arguments to be "promoted"
to unsigned if either is already unsigned.  The preferable rule would be
that if one argument is an int and the other is an unsigned, _both_ should
be promoted to long before the operator is applied.  Unsigned is _not_ a
promotion from int - it is a break-even semantics change.)