xref: /freebsd/lib/libc/quad/floatdidf.c (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This software was developed by the Computer Systems Engineering group
 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
 * contributed to Berkeley.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "quad.h"

/*
 * Convert (signed) quad to double.
 */
double
__floatdidf(quad_t x)
{
	double d;
	union uu u;
	int neg;

	/*
	 * Get an unsigned number first, by negating if necessary.
	 */
	if (x < 0)
		u.q = -x, neg = 1;
	else
		u.q = x, neg = 0;

	/*
	 * Now u.ul[H] has the factor of 2^32 (or whatever) and u.ul[L]
	 * has the units.  Ideally we could just set d, add LONG_BITS to
	 * its exponent, and then add the units, but this is portable
	 * code and does not know how to get at an exponent.  Machine-
	 * specific code may be able to do this more efficiently.
	 */
	d = (double)u.ul[H] * ((1L << (LONG_BITS - 2)) * 4.0);
	d += u.ul[L];

	return (neg ? -d : d);
}