lib/libc/gen/frexp.c

   1 /*-
   2  * Copyright (c) 2004 David Schultz <das@FreeBSD.ORG>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $FreeBSD: src/lib/libc/gen/frexp.c,v 1.1 2004/07/18 21:23:39 das Exp $
  27  */
  28
  29 #include <math.h>
  30
  31 #include "fpmath.h"
  32
  33 double
  34 frexp(double d, int *ex)
  35 {
  36         union IEEEd2bits u;
  37
  38         u.d = d;
  39         switch (u.bits.exp) {
  40         case 0:         /* 0 or subnormal */
  41                 if ((u.bits.manl | u.bits.manh) == 0) {
  42                         *ex = 0;
  43                 } else {
  44                         u.d *= 0x1.0p514;
  45                         *ex = u.bits.exp - 1536;
  46                         u.bits.exp = 1022;
  47                 }
  48                 break;
  49         case 2047:      /* infinity or NaN; value of *ex is unspecified */
  50                 break;
  51         default:        /* normal */
  52                 *ex = u.bits.exp - 1022;
  53                 u.bits.exp = 1022;
  54                 break;
  55         }
  56         return (u.d);
  57 }