lib/libc/quad/floatdidf.c

   1 /*-
   2  * Copyright (c) 1992, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This software was developed by the Computer Systems Engineering group
   6  * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
   7  * contributed to Berkeley.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * @(#)floatdidf.c      8.1 (Berkeley) 6/4/93
  34  * $FreeBSD: src/lib/libc/quad/floatdidf.c,v 1.3 2007/01/09 00:28:03 imp Exp $
  35  */
  36
  37 #include "quad.h"
  38
  39 /*
  40  * Convert (signed) quad to double.
  41  */
  42 double
  43 __floatdidf(quad_t x)
  44 {
  45         double d;
  46         union uu u;
  47         int neg;
  48
  49         /*
  50          * Get an unsigned number first, by negating if necessary.
  51          */
  52         if (x < 0)
  53                 u.q = -x, neg = 1;
  54         else
  55                 u.q = x, neg = 0;
  56
  57         /*
  58          * Now u.ul[H] has the factor of 2^32 (or whatever) and u.ul[L]
  59          * has the units.  Ideally we could just set d, add LONG_BITS to
  60          * its exponent, and then add the units, but this is portable
  61          * code and does not know how to get at an exponent.  Machine-
  62          * specific code may be able to do this more efficiently.
  63          */
  64         d = (double)u.ul[H] * ((1 << (LONG_BITS - 2)) * 4.0);
  65         d += u.ul[L];
  66
  67         return (neg ? -d : d);
  68 }