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 1.7 2007/02/02 23:08:22 christos 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 #ifndef _SYS_IEEE754_H_
   43 #define _SYS_IEEE754_H_
   44 
   45 /*
   46  * NOTICE: This is not a standalone file.  To use it, #include it in
   47  * your port's ieee.h header.
   48  */
   49 
   50 #include <machine/endian.h>
   51 
   52 /*
   53  * <sys/ieee754.h> defines the layout of IEEE 754 floating point types.
   54  * Only single-precision and double-precision types are defined here;
   55  * extended types, if available, are defined in the machine-dependent
   56  * header.
   57  */
   58 
   59 /*
   60  * Define the number of bits in each fraction and exponent.
   61  *
   62  *                   k           k+1
   63  * Note that  1.0 x 2  == 0.1 x 2      and that denorms are represented
   64  *
   65  *                                        (-exp_bias+1)
   66  * as fractions that look like 0.fffff x 2             .  This means that
   67  *
   68  *                       -126
   69  * the number 0.10000 x 2    , for instance, is the same as the normalized
   70  *
   71  *              -127                       -128
   72  * float 1.0 x 2    .  Thus, to represent 2    , we need one leading zero
   73  *
   74  *                                -129
   75  * in the fraction; to represent 2    , we need two, and so on.  This
   76  *
   77  *                                                   (-exp_bias-fracbits+1)
   78  * implies that the smallest denormalized number is 2
   79  *
   80  * for whichever format we are talking about: for single precision, for
   81  *
   82  *                                              -126            -149
   83  * instance, we get .00000000000000000000001 x 2    , or 1.0 x 2    , and
   84  *
   85  * -149 == -127 - 23 + 1.
   86  */
   87 #define SNG_EXPBITS     8
   88 #define SNG_FRACBITS    23
   89 
   90 struct ieee_single {
   91 #if _BYTE_ORDER == _BIG_ENDIAN
   92         u_int   sng_sign:1;
   93         u_int   sng_exp:SNG_EXPBITS;
   94         u_int   sng_frac:SNG_FRACBITS;
   95 #else
   96         u_int   sng_frac:SNG_FRACBITS;
   97         u_int   sng_exp:SNG_EXPBITS;
   98         u_int   sng_sign:1;
   99 #endif
  100 };
  101 
  102 #define DBL_EXPBITS     11
  103 #define DBL_FRACHBITS   20
  104 #define DBL_FRACLBITS   32
  105 #define DBL_FRACBITS    (DBL_FRACHBITS + DBL_FRACLBITS)
  106 
  107 struct ieee_double {
  108 #if _BYTE_ORDER == _BIG_ENDIAN
  109         u_int   dbl_sign:1;
  110         u_int   dbl_exp:DBL_EXPBITS;
  111         u_int   dbl_frach:DBL_FRACHBITS;
  112         u_int   dbl_fracl:DBL_FRACLBITS;
  113 #else
  114         u_int   dbl_fracl:DBL_FRACLBITS;
  115         u_int   dbl_frach:DBL_FRACHBITS;
  116         u_int   dbl_exp:DBL_EXPBITS;
  117         u_int   dbl_sign:1;
  118 #endif
  119 };
  120 
  121 /*
  122  * Floats whose exponent is in [1..INFNAN) (of whatever type) are
  123  * `normal'.  Floats whose exponent is INFNAN are either Inf or NaN.
  124  * Floats whose exponent is zero are either zero (iff all fraction
  125  * bits are zero) or subnormal values.
  126  *
  127  * At least one `signalling NaN' and one `quiet NaN' value must be
  128  * implemented.  It is left to the architecture to specify how to
  129  * distinguish between these.
  130  */
  131 #define SNG_EXP_INFNAN  255
  132 #define DBL_EXP_INFNAN  2047
  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 };
  152 #endif /* _SYS_IEEE754_H_ */

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