1/* FPU control word bits.  x86 version.
  2   Copyright (C) 1993-2025 Free Software Foundation, Inc.
  3   This file is part of the GNU C Library.
  4
  5   The GNU C Library is free software; you can redistribute it and/or
  6   modify it under the terms of the GNU Lesser General Public
  7   License as published by the Free Software Foundation; either
  8   version 2.1 of the License, or (at your option) any later version.
  9
 10   The GNU C Library is distributed in the hope that it will be useful,
 11   but WITHOUT ANY WARRANTY; without even the implied warranty of
 12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 13   Lesser General Public License for more details.
 14
 15   You should have received a copy of the GNU Lesser General Public
 16   License along with the GNU C Library; if not, see
 17   <https://www.gnu.org/licenses/>.  */
 18
 19#ifndef _FPU_CONTROL_H
 20#define _FPU_CONTROL_H	1
 21
 22/* Note that this file sets on x86-64 only the x87 FPU, it does not
 23   touch the SSE unit.  */
 24
 25/* Here is the dirty part. Set up your 387 through the control word
 26 * (cw) register.
 27 *
 28 *     15-13    12  11-10  9-8     7-6     5    4    3    2    1    0
 29 * | reserved | IC | RC  | PC | reserved | PM | UM | OM | ZM | DM | IM
 30 *
 31 * IM: Invalid operation mask
 32 * DM: Denormalized operand mask
 33 * ZM: Zero-divide mask
 34 * OM: Overflow mask
 35 * UM: Underflow mask
 36 * PM: Precision (inexact result) mask
 37 *
 38 * Mask bit is 1 means no interrupt.
 39 *
 40 * PC: Precision control
 41 * 11 - round to extended precision
 42 * 10 - round to double precision
 43 * 00 - round to single precision
 44 *
 45 * RC: Rounding control
 46 * 00 - rounding to nearest
 47 * 01 - rounding down (toward - infinity)
 48 * 10 - rounding up (toward + infinity)
 49 * 11 - rounding toward zero
 50 *
 51 * IC: Infinity control
 52 * That is for 8087 and 80287 only.
 53 *
 54 * The hardware default is 0x037f which we use.
 55 */
 56
 57#include <features.h>
 58
 59/* masking of interrupts */
 60#define _FPU_MASK_IM  0x01
 61#define _FPU_MASK_DM  0x02
 62#define _FPU_MASK_ZM  0x04
 63#define _FPU_MASK_OM  0x08
 64#define _FPU_MASK_UM  0x10
 65#define _FPU_MASK_PM  0x20
 66
 67/* precision control */
 68#define _FPU_EXTENDED 0x300	/* libm requires double extended precision.  */
 69#define _FPU_DOUBLE   0x200
 70#define _FPU_SINGLE   0x0
 71
 72/* rounding control */
 73#define _FPU_RC_NEAREST 0x0    /* RECOMMENDED */
 74#define _FPU_RC_DOWN    0x400
 75#define _FPU_RC_UP      0x800
 76#define _FPU_RC_ZERO    0xC00
 77
 78#define _FPU_RESERVED 0xF0C0  /* Reserved bits in cw */
 79
 80
 81/* The fdlibm code requires strict IEEE double precision arithmetic,
 82   and no interrupts for exceptions, rounding to nearest.  */
 83
 84#define _FPU_DEFAULT  0x037f
 85
 86/* IEEE:  same as above.  */
 87#define _FPU_IEEE     0x037f
 88
 89/* Type of the control word.  */
 90typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));
 91
 92/* Macros for accessing the hardware control word.  "*&" is used to
 93   work around a bug in older versions of GCC.  __volatile__ is used
 94   to support combination of writing the control register and reading
 95   it back.  Without __volatile__, the old value may be used for reading
 96   back under compiler optimization.
 97
 98   Note that the use of these macros is not sufficient anymore with
 99   recent hardware nor on x86-64.  Some floating point operations are
100   executed in the SSE/SSE2 engines which have their own control and
101   status register.  */
102#define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw))
103#define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw))
104
105/* Default control word set at startup.  */
106extern fpu_control_t __fpu_control;
107
108#endif	/* fpu_control.h */