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floatdisf.c revision 1.1 
      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  * 3. All advertising materials mentioning features or use of this software
     18  *    must display the following acknowledgement:
     19  *	This product includes software developed by the University of
     20  *	California, Berkeley and its contributors.
     21  * 4. Neither the name of the University nor the names of its contributors
     22  *    may be used to endorse or promote products derived from this software
     23  *    without specific prior written permission.
     24  *
     25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     35  * SUCH DAMAGE.
     36  */
     37 
     38 #if defined(LIBC_SCCS) && !defined(lint)
     39 /*static char *sccsid = "from: @(#)floatdisf.c	8.1 (Berkeley) 6/4/93";*/
     40 static char *rcsid = "$Id: floatdisf.c,v 1.1 1993/09/16 06:05:59 mycroft Exp $";
     41 #endif /* LIBC_SCCS and not lint */
     42 
     43 #include "quad.h"
     44 
     45 /*
     46  * Convert (signed) quad to float.
     47  */
     48 float
     49 __floatdisf(x)
     50 	quad_t x;
     51 {
     52 	float f;
     53 	union uu u;
     54 	int neg;
     55 
     56 	/*
     57 	 * Get an unsigned number first, by negating if necessary.
     58 	 */
     59 	if (x < 0)
     60 		u.q = -x, neg = 1;
     61 	else
     62 		u.q = x, neg = 0;
     63 
     64 	/*
     65 	 * Now u.ul[H] has the factor of 2^32 (or whatever) and u.ul[L]
     66 	 * has the units.  Ideally we could just set f, add LONG_BITS to
     67 	 * its exponent, and then add the units, but this is portable
     68 	 * code and does not know how to get at an exponent.  Machine-
     69 	 * specific code may be able to do this more efficiently.
     70 	 *
     71 	 * Using double here may be excessive paranoia.
     72 	 */
     73 	f = (double)u.ul[H] * ((1 << (LONG_BITS - 2)) * 4.0);
     74 	f += u.ul[L];
     75 
     76 	return (neg ? -f : f);
     77 }
     78