1/* FPU control word bits. x86 version.
2 Copyright (C) 1993-2020 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. */
91typedef 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. */
107extern fpu_control_t __fpu_control;
108
109#endif /* fpu_control.h */
110