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/* FPU control word bits. x86 version.

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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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* 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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* 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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* Mask bit is 1 means no interrupt.

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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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* 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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* IC: Infinity control

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* That is for 8087 and 80287 only.

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* The hardware default is 0x037f which we use.

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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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