sysdeps/i386/fpu_control.h

   1 /* FPU control word bits.  i387 version.
   2    Copyright (C) 1993,1995-1998,2000,2001,2003 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 Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    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 which we use.
  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     /* libm requires double extended precision.  */
  68 #define _FPU_DOUBLE   0x200
  69 #define _FPU_SINGLE   0x0
  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  0x037f
  84
  85 /* IEEE:  same as above.  */
  86 #define _FPU_IEEE     0x037f
  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
  93    Note that the use of these macros is no sufficient anymore with
  94    recent hardware.  Some floating point operations are executed in
  95    the SSE/SSE2 engines which have their own control and status register.  */
  96 #define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw))
  97 #define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw))
  98
  99 /* Default control word set at startup.  */
 100 extern fpu_control_t __fpu_control;
 101
 102 #endif  /* fpu_control.h */