lib/libc/compat/gen/compat_frexp_ieee754.c

   1 /* $NetBSD: compat_frexp_ieee754.c,v 1.5 2010/04/23 19:04:54 drochner 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  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions and the following disclaimer.
  16  * 2. Redistributions in binary form must reproduce the above copyright
  17  *    notice, this list of conditions and the following disclaimer in the
  18  *    documentation and/or other materials provided with the distribution.
  19  * 3. Neither the name of the University nor the names of its contributors
  20  *    may be used to endorse or promote products derived from this software
  21  *    without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  *
  35  * from: Header: frexp.c,v 1.1 91/07/07 04:45:01 torek Exp
  36  */
  37
  38 #include <sys/cdefs.h>
  39 #if defined(LIBC_SCCS) && !defined(lint)
  40 #if 0
  41 static char sccsid[] = "@(#)frexp.c     8.1 (Berkeley) 6/4/93";
  42 #else
  43 __RCSID("$NetBSD: compat_frexp_ieee754.c,v 1.5 2010/04/23 19:04:54 drochner Exp $");
  44 #endif
  45 #endif /* LIBC_SCCS and not lint */
  46
  47 #include <sys/types.h>
  48 #include <machine/ieee.h>
  49
  50 double frexp(double, int *);
  51
  52 /*
  53  * Split the given value into a fraction in the range [0.5, 1.0) and
  54  * an exponent, such that frac * (2^exp) == value.  If value is 0,
  55  * return 0.
  56  */
  57 double
  58 frexp(double value, int *eptr)
  59 {
  60         union ieee_double_u u;
  61
  62         if (value) {
  63                 /*
  64                  * Fractions in [0.5..1.0) have an exponent of 2^-1.
  65                  * Leave Inf and NaN alone, however.
  66                  */
  67                 u.dblu_d = value;
  68                 if (u.dblu_dbl.dbl_exp != DBL_EXP_INFNAN) {
  69                         *eptr = 0;
  70                         if (u.dblu_dbl.dbl_exp == 0) {
  71                                 /* denormal, scale out of mantissa */
  72                                 *eptr = -DBL_FRACBITS;
  73                                 u.dblu_d *= 4.50359962737049600000e+15;
  74                         }
  75                         *eptr += u.dblu_dbl.dbl_exp - (DBL_EXP_BIAS - 1);
  76                         u.dblu_dbl.dbl_exp = DBL_EXP_BIAS - 1;
  77                 }
  78                 return (u.dblu_d);
  79         } else {
  80                 *eptr = 0;
  81                 return (value);
  82         }
  83 }