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The C and C++ Include Header Files

/usr/include/x86_64-linux-gnu/fpu_control.h


$ cat -n /usr/include/x86_64-linux-gnu/fpu_control.h

     1	/* FPU control word bits.  x86 version.
     2	   Copyright (C) 1993-2024 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 */