Re: Undefined result vs. int's holding undefined values.

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Article #4600

#4600

From: Henry Spencer
Date: Tue, 09 Jan 1996 19:50

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> Does an appropriate "SAFE TEST" exist
>for multiple.  Has anyone actually seen a real production program where every
>calculation was protected against overflow/underflow.

Safe tests exist for all the arithmetic operations, although you have to
be careful and clever.  See the paper "On Legality Assertions in Euclid",
by Dave Wortman in the July 1979 IEEE Transactions on Software Engineering,
for a fairly complete discussion of the matter.

A program in which overflow/underflow can occur is a buggy program.  In
most cases, the nature of the program is such that the calculations
can be shown not to overflow/underflow.  Where this is not so, checks
are necessary for a reliable program.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

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Path: arc1-ca.pugleaf.net!info.physics.utoronto.ca!utzoo!spenford!henry
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Undefined result vs. int's holding undefined values.
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Date: Tue, 9 Jan 1996 19:50:08 GMT
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