I've noticed that we change the default setting for floating point
precision from extended precision (64-bit) to double precision (53-bit).
The comment in npx.h says:
/*
* The hardware default control word for i387's and later coprocessors is
* 0x37F, giving:
*
* round to nearest
* 64-bit precision
* all exceptions masked.
*
* We modify the affine mode bit and precision bits in this to give:
*
* affine mode for 287's (if they work at all) (1 in bitfield 1<<12)
* 53-bit precision (2 in bitfield 3<<8)
*
* 64-bit precision often gives bad results with high level languages
* because it makes the results of calculations depend on whether
* intermediate values are stored in memory or in FPU registers.
*/
#define __INITIAL_NPXCW__ 0x127F
Oddly, this causes problems with GNAT (Ada is a high level language)
because it wants/expects 64-bit extended precision. It seems as if
GNAT for linux-i386 also uses 64-bit extended precision. The only
other GNAT i386 platform that doesn't use 64-bit precision is NT.
So is the above comment still valid?
--
Dan Eischen
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