sysdeps/i386/fpu_control.h

   1 /* FPU control word bits.  i387 version.
   2    Copyright (C) 1993, 1995, 1996, 1997, 1998 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Olaf Flebbe.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #ifndef _FPU_CONTROL_H
  22 #define _FPU_CONTROL_H  1
  23
  24 /* Here is the dirty part. Set up your 387 through the control word
  25  * (cw) register.
  26  *
  27  *     15-13    12  11-10  9-8     7-6     5    4    3    2    1    0
  28  * | reserved | IC | RC  | PC | reserved | PM | UM | OM | ZM | DM | IM
  29  *
  30  * IM: Invalid operation mask
  31  * DM: Denormalized operand mask
  32  * ZM: Zero-divide mask
  33  * OM: Overflow mask
  34  * UM: Underflow mask
  35  * PM: Precision (inexact result) mask
  36  *
  37  * Mask bit is 1 means no interrupt.
  38  *
  39  * PC: Precision control
  40  * 11 - round to extended precision
  41  * 10 - round to double precision
  42  * 00 - round to single precision
  43  *
  44  * RC: Rounding control
  45  * 00 - rounding to nearest
  46  * 01 - rounding down (toward - infinity)
  47  * 10 - rounding up (toward + infinity)
  48  * 11 - rounding toward zero
  49  *
  50  * IC: Infinity control
  51  * That is for 8087 and 80287 only.
  52  *
  53  * The hardware default is 0x037f. I choose 0x1372.
  54  */
  55
  56 #include <features.h>
  57
  58 /* masking of interrupts */
  59 #define _FPU_MASK_IM  0x01
  60 #define _FPU_MASK_DM  0x02
  61 #define _FPU_MASK_ZM  0x04
  62 #define _FPU_MASK_OM  0x08
  63 #define _FPU_MASK_UM  0x10
  64 #define _FPU_MASK_PM  0x20
  65
  66 /* precision control */
  67 #define _FPU_EXTENDED 0x300
  68 #define _FPU_DOUBLE   0x200     /* fdlibm requires double precision */
  69 #define _FPU_SINGLE   0x0     /* DO NOT USE */
  70
  71 /* rounding control */
  72 #define _FPU_RC_NEAREST 0x0    /* RECOMMENDED */
  73 #define _FPU_RC_DOWN    0x400
  74 #define _FPU_RC_UP      0x800
  75 #define _FPU_RC_ZERO    0xC00
  76
  77 #define _FPU_RESERVED 0xF0C0  /* Reserved bits in cw */
  78
  79
  80 /* The fdlibm code requires strict IEEE double precision arithmetic,
  81    and no interrupts for exceptions, rounding to nearest.  */
  82
  83 #define _FPU_DEFAULT  0x137f
  84
  85 /* IEEE:  same as above.  */
  86 #define _FPU_IEEE     0x137f
  87
  88 /* Type of the control word.  */
  89 typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));
  90
  91 /* Macros for accessing the hardware control word.  */
  92 #define _FPU_GETCW(cw) __asm__ ("fnstcw %0" : "=m" (*&cw))
  93 #define _FPU_SETCW(cw) __asm__ ("fldcw %0" : : "m" (*&cw))
  94
  95 /* Default control word set at startup.  */
  96 extern fpu_control_t __fpu_control;
  97
  98 #endif  /* fpu_control.h */