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