sysdeps/x86/fpu_control.h

   1 /* FPU control word bits.  x86 version.
   2    Copyright (C) 1993-2021 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, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #ifndef _FPU_CONTROL_H
  21 #define _FPU_CONTROL_H  1
  22
  23 /* Note that this file sets on x86-64 only the x87 FPU, it does not
  24    touch the SSE unit.  */
  25
  26 /* Here is the dirty part. Set up your 387 through the control word
  27  * (cw) register.
  28  *
  29  *     15-13    12  11-10  9-8     7-6     5    4    3    2    1    0
  30  * | reserved | IC | RC  | PC | reserved | PM | UM | OM | ZM | DM | IM
  31  *
  32  * IM: Invalid operation mask
  33  * DM: Denormalized operand mask
  34  * ZM: Zero-divide mask
  35  * OM: Overflow mask
  36  * UM: Underflow mask
  37  * PM: Precision (inexact result) mask
  38  *
  39  * Mask bit is 1 means no interrupt.
  40  *
  41  * PC: Precision control
  42  * 11 - round to extended precision
  43  * 10 - round to double precision
  44  * 00 - round to single precision
  45  *
  46  * RC: Rounding control
  47  * 00 - rounding to nearest
  48  * 01 - rounding down (toward - infinity)
  49  * 10 - rounding up (toward + infinity)
  50  * 11 - rounding toward zero
  51  *
  52  * IC: Infinity control
  53  * That is for 8087 and 80287 only.
  54  *
  55  * The hardware default is 0x037f which we use.
  56  */
  57
  58 #include <features.h>
  59
  60 /* masking of interrupts */
  61 #define _FPU_MASK_IM  0x01
  62 #define _FPU_MASK_DM  0x02
  63 #define _FPU_MASK_ZM  0x04
  64 #define _FPU_MASK_OM  0x08
  65 #define _FPU_MASK_UM  0x10
  66 #define _FPU_MASK_PM  0x20
  67
  68 /* precision control */
  69 #define _FPU_EXTENDED 0x300     /* libm requires double extended precision.  */
  70 #define _FPU_DOUBLE   0x200
  71 #define _FPU_SINGLE   0x0
  72
  73 /* rounding control */
  74 #define _FPU_RC_NEAREST 0x0    /* RECOMMENDED */
  75 #define _FPU_RC_DOWN    0x400
  76 #define _FPU_RC_UP      0x800
  77 #define _FPU_RC_ZERO    0xC00
  78
  79 #define _FPU_RESERVED 0xF0C0  /* Reserved bits in cw */
  80
  81
  82 /* The fdlibm code requires strict IEEE double precision arithmetic,
  83    and no interrupts for exceptions, rounding to nearest.  */
  84
  85 #define _FPU_DEFAULT  0x037f
  86
  87 /* IEEE:  same as above.  */
  88 #define _FPU_IEEE     0x037f
  89
  90 /* Type of the control word.  */
  91 typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));
  92
  93 /* Macros for accessing the hardware control word.  "*&" is used to
  94    work around a bug in older versions of GCC.  __volatile__ is used
  95    to support combination of writing the control register and reading
  96    it back.  Without __volatile__, the old value may be used for reading
  97    back under compiler optimization.
  98
  99    Note that the use of these macros is not sufficient anymore with
 100    recent hardware nor on x86-64.  Some floating point operations are
 101    executed in the SSE/SSE2 engines which have their own control and
 102    status register.  */
 103 #define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw))
 104 #define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw))
 105
 106 /* Default control word set at startup.  */
 107 extern fpu_control_t __fpu_control;
 108
 109 #endif  /* fpu_control.h */