Current File : //usr/include/x86_64-linux-gnu/fpu_control.h
/* FPU control word bits. x86 version.
Copyright (C) 1993-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _FPU_CONTROL_H
#define _FPU_CONTROL_H 1
/* Note that this file sets on x86-64 only the x87 FPU, it does not
touch the SSE unit. */
/* Here is the dirty part. Set 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 which we use.
*/
#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 /* libm requires double extended precision. */
#define _FPU_DOUBLE 0x200
#define _FPU_SINGLE 0x0
/* 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 0x037f
/* IEEE: same as above. */
#define _FPU_IEEE 0x037f
/* Type of the control word. */
typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));
/* Macros for accessing the hardware control word. "*&" is used to
work around a bug in older versions of GCC. __volatile__ is used
to support combination of writing the control register and reading
it back. Without __volatile__, the old value may be used for reading
back under compiler optimization.
Note that the use of these macros is not sufficient anymore with
recent hardware nor on x86-64. Some floating point operations are
executed in the SSE/SSE2 engines which have their own control and
status register. */
#define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw))
#define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw))
/* Default control word set at startup. */
extern fpu_control_t __fpu_control;
#endif /* fpu_control.h */
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