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[Gcl-devel] Re: m68k gcl/maxima: Minor Floating point errors

From: Camm Maguire
Subject: [Gcl-devel] Re: m68k gcl/maxima: Minor Floating point errors
Date: 20 Sep 2002 09:17:49 -0400


Rick Younie <address@hidden> writes:

> Camm Maguire wrote:
> > Greetings!  I have one Debian machine (m68k) which is producing very
> > small numerical discrepancies on the results of the two floating point
> > intensive tests in rtest8.mac:
> Hi,
> That rang a bell.  There's this in the gcc man page:
>        -ffloat-store
>               Do  not  store floating point variables in registers.  This pre-
>               vents undesirable excess precision on machines such as the 68000
>               where  the floating registers (of the 68881) keep more precision
>               than a double is supposed to have.
>               For most programs, the excess precision does only  good,  but  a
>               few  programs  rely  on  the precise definition of IEEE floating
>               point.  Use `-ffloat-store' for such programs.

That did it -- thanks!  As Richard Fateman observed, its quite
surprising the magnitude of the difference was so large.  Apparently
m68k has the more accurate answer, right?  In any case, I'm adding
-ffloat-store to gcl's compile flags on m68k to avoid testing

Take care,

> Rick
> -- 

Camm Maguire                                            address@hidden
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah

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