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Add some comments about what the control words do.

This commit is contained in:
mycroft 1998-01-24 14:00:36 +00:00
parent a963fe5864
commit d664bf39b8
1 changed files with 14 additions and 7 deletions
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21
sys/arch/i386/include/npx.h
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@ -1,4 +1,4 @@
/* $NetBSD: npx.h,v 1.12 1998/01/24 13:19:57 mycroft Exp $ */
/* $NetBSD: npx.h,v 1.13 1998/01/24 14:00:36 mycroft Exp $ */
/*-
* Copyright (c) 1990 The Regents of the University of California.
@ -88,14 +88,21 @@ struct emcsts {
long em_dl; /* memory mapped D low register when swtched */
};
/*
* The i387 defaults to Intel extended precision mode and round to nearest,
* with all exceptions masked.
*/
#define __INITIAL_NPXCW__ 0x037f
/* Intel prefers long real (53 bit) precision. */
#define __iBCS2_NPXCW__ 0x0262
/* NetBSD uses double precision with IEEE rounding and (lack of) exceptions. */
/* NetBSD uses IEEE double precision. */
#define __NetBSD_NPXCW__ 0x127f
#define __FreeBSD_NPXCW__ 0x1272 /* XXX */
#define __Linux_NPXCW__ 0x037f /* XXX */
#define __SVR4_NPXCW__ 0x0262 /* XXX */
/* FreeBSD leaves some exceptions unmasked as well. */
#define __FreeBSD_NPXCW__ 0x1272
/* iBCS2 goes a bit further and leaves the underflow exception unmasked. */
#define __iBCS2_NPXCW__ 0x0262
/* Linux just uses the default control word. */
#define __Linux_NPXCW__ 0x037f
/* SVR4 uses the same control word as iBCS2. */
#define __SVR4_NPXCW__ 0x0262
/*
* The standard control word from finit is 0x37F, giving: