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110 lines
3.5 KiB
C
110 lines
3.5 KiB
C
/* FPU control word bits. x86 version.
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Copyright (C) 1993-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Olaf Flebbe.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _FPU_CONTROL_H
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#define _FPU_CONTROL_H 1
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/* Note that this file sets on x86-64 only the x87 FPU, it does not
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touch the SSE unit. */
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/* Here is the dirty part. Set up your 387 through the control word
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* (cw) register.
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*
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* 15-13 12 11-10 9-8 7-6 5 4 3 2 1 0
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* | reserved | IC | RC | PC | reserved | PM | UM | OM | ZM | DM | IM
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*
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* IM: Invalid operation mask
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* DM: Denormalized operand mask
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* ZM: Zero-divide mask
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* OM: Overflow mask
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* UM: Underflow mask
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* PM: Precision (inexact result) mask
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*
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* Mask bit is 1 means no interrupt.
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*
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* PC: Precision control
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* 11 - round to extended precision
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* 10 - round to double precision
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* 00 - round to single precision
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*
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* RC: Rounding control
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* 00 - rounding to nearest
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* 01 - rounding down (toward - infinity)
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* 10 - rounding up (toward + infinity)
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* 11 - rounding toward zero
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*
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* IC: Infinity control
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* That is for 8087 and 80287 only.
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*
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* The hardware default is 0x037f which we use.
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*/
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#include <features.h>
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/* masking of interrupts */
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#define _FPU_MASK_IM 0x01
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#define _FPU_MASK_DM 0x02
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#define _FPU_MASK_ZM 0x04
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#define _FPU_MASK_OM 0x08
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#define _FPU_MASK_UM 0x10
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#define _FPU_MASK_PM 0x20
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/* precision control */
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#define _FPU_EXTENDED 0x300 /* libm requires double extended precision. */
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#define _FPU_DOUBLE 0x200
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#define _FPU_SINGLE 0x0
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/* rounding control */
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#define _FPU_RC_NEAREST 0x0 /* RECOMMENDED */
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#define _FPU_RC_DOWN 0x400
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#define _FPU_RC_UP 0x800
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#define _FPU_RC_ZERO 0xC00
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#define _FPU_RESERVED 0xF0C0 /* Reserved bits in cw */
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/* The fdlibm code requires strict IEEE double precision arithmetic,
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and no interrupts for exceptions, rounding to nearest. */
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#define _FPU_DEFAULT 0x037f
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/* IEEE: same as above. */
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#define _FPU_IEEE 0x037f
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/* Type of the control word. */
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typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__)));
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/* Macros for accessing the hardware control word. "*&" is used to
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work around a bug in older versions of GCC. __volatile__ is used
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to support combination of writing the control register and reading
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it back. Without __volatile__, the old value may be used for reading
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back under compiler optimization.
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Note that the use of these macros is not sufficient anymore with
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recent hardware nor on x86-64. Some floating point operations are
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executed in the SSE/SSE2 engines which have their own control and
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status register. */
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#define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw))
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#define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw))
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/* Default control word set at startup. */
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extern fpu_control_t __fpu_control;
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#endif /* fpu_control.h */
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