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Updated bde's comments wrt. i387 control word settings so that they 

describe NetBSD, rather than 386BSD 0.1.
Removed 386BSD and BDE control word constants, since we don't need and
will never use them.  However, The iBCS control word constant is kept,
since we might want to use it in the iBCS binary compatibility code.
This commit is contained in:
jtc 1994-09-22 00:37:13 +00:00
parent 97fc5017d9
commit 62db8972b1
1 changed files with 12 additions and 30 deletions
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42
sys/arch/i386/include/npx.h
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@ -34,7 +34,7 @@
* SUCH DAMAGE.
*
* from: @(#)npx.h 5.3 (Berkeley) 1/18/91
* $Id: npx.h,v 1.9 1994/01/25 19:58:30 jtc Exp $
* $Id: npx.h,v 1.10 1994/09/22 00:37:13 jtc Exp $
*/
/*
@ -89,49 +89,31 @@ struct emcsts {
/* Intel prefers long real (53 bit) precision */
#define __iBCS_NPXCW__ 0x262
/* wfj prefers temporary real (64 bit) precision */
#define __386BSD_NPXCW__ 0x362
/* */
#define __NetBSD_NPXCW__ 0x127f
/*
* bde prefers 53 bit precision and all exceptions masked.
*
* The standard control word from finit is 0x37F, giving:
*
* round to nearest
* 64-bit precision
* all exceptions masked.
*
* Now I want:
*
* affine mode for 287's (if they work at all) (1 in bitfield 1<<12)
* 53-bit precision (2 in bitfield 3<<8)
* overflow exception unmasked (0 in bitfield 1<<3)
* zero divide exception unmasked (0 in bitfield 1<<2)
* invalid-operand exception unmasked (0 in bitfield 1<<0).
* Now we want:
* affine mode (if we decide to support 287's)
* round to nearest
* 53-bit precision
* all exceptions masked.
*
* 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.
*
* The "Intel" and wfj control words have:
*
* underflow exception unmasked (0 in bitfield 1<<4)
*
* but that causes an unexpected exception in the test program 'paranoia'
* and makes denormals useless (DBL_MIN / 2 underflows). It doesn't make
* a lot of sense to trap underflow without trapping denormals.
*
* Later I will want the IEEE default of all exceptions masked. See the
* 0.0 math manpage for why this is better. The 0.1 math manpage is empty.
* The iBCS control word has underflow, overflow, zero divide, and invalid
* operation exceptions unmasked. But that causes an unexpected exception
* in the test program 'paranoia' and makes denormals useless (DBL_MIN / 2
* underflows). It doesn't make a lot of sense to trap underflow without
* trapping denormals.
*/
#define __BDE_NPXCW__ 0x1272
#define __BETTER_BDE_NPXCW__ 0x127f
#ifdef __NetBSD__
#define __INITIAL_NPXCW__ __NetBSD_NPXCW__
#else
#define __INITIAL_NPXCW__ __iBCS_NPXCW__
#endif
#endif /* !_I386_NPX_H_ */