Re: Low-order uncertainty in 87 math processing

William D Clinger <will@ccs.neu.edu>
27 Sep 1997 01:10:53 -0400

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Related articles
Low-order uncertainty in 87 math processing solmaker@olympus.net (1997-09-24)
Re: Low-order uncertainty in 87 math processing dlmoore@ix.netcom.com (David L Moore) (1997-09-24)
Re: Low-order uncertainty in 87 math processing will@ccs.neu.edu (William D Clinger) (1997-09-27)
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From: William D Clinger <will@ccs.neu.edu>
Newsgroups: comp.compilers
Date: 27 Sep 1997 01:10:53 -0400
Organization: Northeastern University
References: 97-09-092 97-09-102
Keywords: errors, arithmetic

> x:=y;
> [code not changing x or y]
> q:=x-y;
> [ why is q not zero]


David L Moore's suggestion (that the compiler's choice between
memory and floating point registers can affect precision) would
explain why q is not always zero, and John's suggestion (that
the precision control flags are being changed) would then explain
why the problem sometimes goes away until reboot.


Will
--

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