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

From: Raymond Toy
Subject: [Gcl-devel] Re: [Maxima] Re: m68k gcl/maxima: Minor Floating point errors
Date: 30 Sep 2002 10:54:46 -0400
User-agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.5 (brussels sprouts)

>>>>> "Camm" == Camm Maguire <address@hidden> writes:

    Camm> Greetings!
    Camm> 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.

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

But does gcl on x86 also do a -ffloat-store?  x86 also keeps extra
precision, so I would have expected similar issues on x86.


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