xref: /freebsd/lib/libc/quad/fixunsdfdi.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"

#define	ONE_FOURTH	(1L << (LONG_BITS - 2))
#define	ONE_HALF	(ONE_FOURTH * 2.0)
#define	ONE		(ONE_FOURTH * 4.0)

/*
 * Convert double to (unsigned) quad.
 * Not sure what to do with negative numbers---for now, anything out
 * of range becomes UQUAD_MAX.
 */
u_quad_t
__fixunsdfdi(double x)
{
	double toppart;
	union uu t;

	if (x < 0)
		return (UQUAD_MAX);	/* ??? should be 0?  ERANGE??? */
#ifdef notdef				/* this falls afoul of a GCC bug */
	if (x >= UQUAD_MAX)
		return (UQUAD_MAX);
#else					/* so we wire in 2^64-1 instead */
	if (x >= 18446744073709551615.0)
		return (UQUAD_MAX);
#endif
	/*
	 * Get the upper part of the result.  Note that the divide
	 * may round up; we want to avoid this if possible, so we
	 * subtract `1/2' first.
	 */
	toppart = (x - ONE_HALF) / ONE;
	/*
	 * Now build a u_quad_t out of the top part.  The difference
	 * between x and this is the bottom part (this may introduce
	 * a few fuzzy bits, but what the heck).  With any luck this
	 * difference will be nonnegative: x should wind up in the
	 * range [0..ULONG_MAX].  For paranoia, we assume [LONG_MIN..
	 * 2*ULONG_MAX] instead.
	 */
	t.ul[H] = (unsigned long)toppart;
	t.ul[L] = 0;
	x -= (double)t.uq;
	if (x < 0) {
		t.ul[H]--;
		x += (double)ULONG_MAX;
	}
	if (x > (double)ULONG_MAX) {
		t.ul[H]++;
		x -= (double)ULONG_MAX;
	}
	t.ul[L] = (u_long)x;
	return (t.uq);
}