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From: 5114djh@hound.UUCP (D.HOUCK)
Newsgroups: net.micro.pc
Subject: Re: MS FORTRAN integer multiplying
Message-ID: <374@hound.UUCP>
Date: Fri, 13-Jan-84 10:01:43 EST
Article-I.D.: hound.374
Posted: Fri Jan 13 10:01:43 1984
Date-Received: Sat, 14-Jan-84 03:32:06 EST
Organization: Bell Labs, Holmdel NJ
Lines: 16

I have just started running MS FORTRAN (V3.13) and decided to
check it out with a simulation program I had run on other machines.
When it didn't run correctly I traced the problem to the random
number generator that I had used.  This is the standard congruential 
method that assumes 2's complement representation of 32-bit integers 
and overflows are thrown away.  However, it appears that large integer
multiplications do not work as expected.
As a simple example, the product of 2 and 1073741824(2**30)
resulted in an answer of -131072(-2**17).
The answer normally is the number with bit representation of a one 
followed by 31 zeros. Whatever you want to call that number, it's not -2**17.
   I would like to know if anyone has experienced similar problems
or if anyone knows how integer overflows are handled in MS FORTRAN.

                            David Houck
                            AT&T Bell Laboratories