The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/sys/ieee754.h

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    1 /*      $NetBSD: ieee754.h,v 1.4 2003/10/27 02:30:26 simonb Exp $       */
    2 
    3 /*
    4  * Copyright (c) 1992, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * This software was developed by the Computer Systems Engineering group
    8  * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
    9  * contributed to Berkeley.
   10  *
   11  * All advertising materials mentioning features or use of this software
   12  * must display the following acknowledgement:
   13  *      This product includes software developed by the University of
   14  *      California, Lawrence Berkeley Laboratory.
   15  *
   16  * Redistribution and use in source and binary forms, with or without
   17  * modification, are permitted provided that the following conditions
   18  * are met:
   19  * 1. Redistributions of source code must retain the above copyright
   20  *    notice, this list of conditions and the following disclaimer.
   21  * 2. Redistributions in binary form must reproduce the above copyright
   22  *    notice, this list of conditions and the following disclaimer in the
   23  *    documentation and/or other materials provided with the distribution.
   24  * 3. Neither the name of the University nor the names of its contributors
   25  *    may be used to endorse or promote products derived from this software
   26  *    without specific prior written permission.
   27  *
   28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   38  * SUCH DAMAGE.
   39  *
   40  *      @(#)ieee.h      8.1 (Berkeley) 6/11/93
   41  */
   42 
   43 /*
   44  * NOTICE: This is not a standalone file.  To use it, #include it in
   45  * your port's ieee.h header.
   46  */
   47 
   48 #include <machine/endian.h>
   49 
   50 /*
   51  * <sys/ieee754.h> defines the layout of IEEE 754 floating point types.
   52  * Only single-precision and double-precision types are defined here;
   53  * extended types, if available, are defined in the machine-dependent
   54  * header.
   55  */
   56 
   57 /*
   58  * Define the number of bits in each fraction and exponent.
   59  *
   60  *                   k           k+1
   61  * Note that  1.0 x 2  == 0.1 x 2      and that denorms are represented
   62  *
   63  *                                        (-exp_bias+1)
   64  * as fractions that look like 0.fffff x 2             .  This means that
   65  *
   66  *                       -126
   67  * the number 0.10000 x 2    , for instance, is the same as the normalized
   68  *
   69  *              -127                       -128
   70  * float 1.0 x 2    .  Thus, to represent 2    , we need one leading zero
   71  *
   72  *                                -129
   73  * in the fraction; to represent 2    , we need two, and so on.  This
   74  *
   75  *                                                   (-exp_bias-fracbits+1)
   76  * implies that the smallest denormalized number is 2
   77  *
   78  * for whichever format we are talking about: for single precision, for
   79  *
   80  *                                              -126            -149
   81  * instance, we get .00000000000000000000001 x 2    , or 1.0 x 2    , and
   82  *
   83  * -149 == -127 - 23 + 1.
   84  */
   85 #define SNG_EXPBITS     8
   86 #define SNG_FRACBITS    23
   87 
   88 #define DBL_EXPBITS     11
   89 #define DBL_FRACBITS    52
   90 
   91 struct ieee_single {
   92 #if _BYTE_ORDER == _BIG_ENDIAN
   93         u_int   sng_sign:1;
   94         u_int   sng_exp:8;
   95         u_int   sng_frac:23;
   96 #else
   97         u_int   sng_frac:23;
   98         u_int   sng_exp:8;
   99         u_int   sng_sign:1;
  100 #endif
  101 };
  102 
  103 struct ieee_double {
  104 #if _BYTE_ORDER == _BIG_ENDIAN
  105         u_int   dbl_sign:1;
  106         u_int   dbl_exp:11;
  107         u_int   dbl_frach:20;
  108         u_int   dbl_fracl;
  109 #else
  110         u_int   dbl_fracl;
  111         u_int   dbl_frach:20;
  112         u_int   dbl_exp:11;
  113         u_int   dbl_sign:1;
  114 #endif
  115 };
  116 
  117 /*
  118  * Floats whose exponent is in [1..INFNAN) (of whatever type) are
  119  * `normal'.  Floats whose exponent is INFNAN are either Inf or NaN.
  120  * Floats whose exponent is zero are either zero (iff all fraction
  121  * bits are zero) or subnormal values.
  122  *
  123  * A NaN is a `signalling NaN' if its QUIETNAN bit is clear in its
  124  * high fraction; if the bit is set, it is a `quiet NaN'.
  125  */
  126 #define SNG_EXP_INFNAN  255
  127 #define DBL_EXP_INFNAN  2047
  128 
  129 #if 0
  130 #define SNG_QUIETNAN    (1 << 22)
  131 #define DBL_QUIETNAN    (1 << 19)
  132 #endif
  133 
  134 /*
  135  * Exponent biases.
  136  */
  137 #define SNG_EXP_BIAS    127
  138 #define DBL_EXP_BIAS    1023
  139 
  140 /*
  141  * Convenience data structures.
  142  */
  143 union ieee_single_u {
  144         float                   sngu_f;
  145         struct ieee_single      sngu_sng;
  146 };
  147 
  148 union ieee_double_u {
  149         double                  dblu_d;
  150         struct ieee_double      dblu_dbl;
  151 };

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