glibc/sysdeps/i386/fpu_control.h

/* FPU control word bits.  i387 version.
Copyright (C) 1993, 1995, 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Olaf Flebbe.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#ifndef _FPU_CONTROL_H
#define _FPU_CONTROL_H

/* Here is the dirty part. Settup up your 387 through the control word
 * (cw) register.
 *
 *     15-13    12  11-10  9-8     7-6     5    4    3    2    1    0
 * | reserved | IC | RC  | PC | reserved | PM | UM | OM | ZM | DM | IM
 *
 * IM: Invalid operation mask
 * DM: Denormalized operand mask
 * ZM: Zero-divide mask
 * OM: Overflow mask
 * UM: Underflow mask
 * PM: Precision (inexact result) mask
 *
 * Mask bit is 1 means no interrupt.
 *
 * PC: Precision control
 * 11 - round to extended precision
 * 10 - round to double precision
 * 00 - round to single precision
 *
 * RC: Rounding control
 * 00 - rounding to nearest
 * 01 - rounding down (toward - infinity)
 * 10 - rounding up (toward + infinity)
 * 11 - rounding toward zero
 *
 * IC: Infinity control
 * That is for 8087 and 80287 only.
 *
 * The hardware default is 0x037f. I choose 0x1372.
 */

#include <features.h>

/* masking of interrupts */
#define _FPU_MASK_IM  0x01
#define _FPU_MASK_DM  0x02
#define _FPU_MASK_ZM  0x04
#define _FPU_MASK_OM  0x08
#define _FPU_MASK_UM  0x10
#define _FPU_MASK_PM  0x20

/* precision control */
#define _FPU_EXTENDED 0x300
#define _FPU_DOUBLE   0x200	/* fdlibm requires double precision */
#define _FPU_SINGLE   0x0     /* DO NOT USE */

/* rounding control */
#define _FPU_RC_NEAREST 0x0    /* RECOMMENDED */
#define _FPU_RC_DOWN    0x400
#define _FPU_RC_UP      0x800
#define _FPU_RC_ZERO    0xC00

#define _FPU_RESERVED 0xF0C0  /* Reserved bits in cw */


/* The fdlibm code requires strict IEEE double precision arithmetic,
   and no interrupts for exceptions, rounding to nearest.  */

#define _FPU_DEFAULT  0x127f

/* IEEE:  same as above, but exceptions */
#define _FPU_IEEE     0x127f

/* Type of the control word.  */
typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));

/* Macros for accessing the hardware control word.  */
#define _FPU_GETCW(cw) __asm__ ("fnstcw %0" : "=m" (cw))
#define _FPU_SETCW(cw) __asm__ ("fldcw %0" : : "m" (cw))

/* Default control word set at startup.  */
extern fpu_control_t __fpu_control;

__BEGIN_DECLS

/* Called at startup.  It can be used to manipulate fpu control register.  */
extern void __setfpucw __P ((fpu_control_t));

__END_DECLS

#endif	/* fpu_control.h */