glibc (2.38)
1 /* FPU control word bits. x86 version.
2 Copyright (C) 1993-2023 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. */
90 typedef 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. */
106 extern fpu_control_t __fpu_control;
107
108 #endif /* fpu_control.h */
Browse
Usage
Versions