1 /* FPU control word bits. x86 version. 2 Copyright (C) 1993-2012 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 <http://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. */ 91 typedef 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. */ 107 extern fpu_control_t __fpu_control; 108 109 #endif /* fpu_control.h */ 110