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[Gcl-devel] Re: [Maxima] Re: m68k gcl/maxima: Minor Floating point error
[Gcl-devel] Re: [Maxima] Re: m68k gcl/maxima: Minor Floating point errors
Fri, 20 Sep 2002 15:42:55 -0700
From: Camm Maguire <address@hidden>
Greetings, and thanks for pointing this out. Actually, I maintain a
few numerical packages requiring this flag on m68k to pass the
regression tests in the package (gcl/maxima, atlas, blas, lapack,...).
I suppose the sacrifice of performance is the correct approach.
Anyone actually using the 68k with a different opinion will likely
sway my mind in the other direction :). This would of course require
sidestepping integrity tests in this case, as I won't have the time to
maintain dual sets of expected results.
I actually think you have done the wise thing, but if any 68K fanatics
insist otherwise, I've just checked my venerable 68881/68882 manual.
There is a two-bit field in the FPCR Mode Control Byte that specifies
the rounding precision for any fp calculation, and setting it forces
IEEE-standard calculation. The manual warns, however, that these are
intended for emulation of machines that only support these precisions,
and that there is a significant speed cost when the single- or
double-float rounding is turned on. Also, OS's and libraries make it
nototiously difficult to manupulate FP control registers, and are even
more notoriously sloppy about preserving the values in control