1/*	$NetBSD: fixunsgen_ieee754.c,v 1.1 2011/07/09 02:30:27 matt Exp $	*/
2
3/*-
4 * Copyright (c) 1992, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 *    notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in the
18 *    documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36#include <sys/cdefs.h>
37
38#if !defined(FIXUNSNAME) && defined(LIBC_SCCS) && !defined(lint)
39__RCSID("$NetBSD: fixunsgen_ieee754.c,v 1.1 2011/07/09 02:30:27 matt Exp $");
40#endif /* LIBC_SCCS and not lint */
41
42#include <stddef.h>
43#include <stdint.h>
44#include <stdbool.h>
45#include <float.h>
46
47#ifndef FIXUNSNAME
48#define	FIXUNSNAME(n)	n##32
49#define	UINTXX_T	uint32_t
50#endif
51
52__dso_hidden UINTXX_T
53	FIXUNSNAME(__fixunsgen)(int, bool, size_t, size_t, const uint32_t *);
54
55/*
56 * Convert double to (unsigned) int.  All operations are done module 2^32.
57 */
58UINTXX_T
59FIXUNSNAME(__fixunsgen)(int exp, bool sign, size_t mant_dig, size_t fracbits,
60	const uint32_t *frac)
61{
62	UINTXX_T tmp;
63
64	/*
65	 * If it's less than 1 (negative exponent), it's going to round
66	 * to zero.  If the exponent is so large that it is a multiple of
67	 * 2^N, then x module 2^N will be 0.  (we use the fact treating a
68	 * negative value as unsigned will be greater than nonnegative value)
69	 */
70	if (__predict_false((size_t)exp >= mant_dig + sizeof(UINTXX_T)*8))
71		return 0;
72
73	/*
74	 * This is simplier than it seems.  Basically we are constructing
75	 * fixed binary representation of the floating point number tossing
76	 * away bits that wont be in the modulis we return.
77	 */
78	tmp = 1;
79	for (size_t ebits = exp;;) {
80		if (ebits <= fracbits) {
81			/*
82			 * The current fraction has more bits than we need.
83			 * Shift the current value over and insert the bits
84			 * we want.  We're done.
85			 */
86			tmp <<= ebits;
87			tmp |= *frac >> (fracbits - ebits);
88			break;
89		}
90		if (fracbits == sizeof(tmp)*4) {
91			/*
92			 * Shifts must be < sizeof(type).  If it's going to be
93			 * sizeof(type), just replace the value.
94			 */
95			tmp = *frac--;
96		} else {
97			tmp <<= fracbits;
98			tmp |= *frac--;
99		}
100		ebits -= fracbits;
101		fracbits = sizeof(frac[0]) * 4;
102	}
103
104	/*
105	 * If the input was negative, make tmp negative module 2^32.
106	 */
107	if (sign)
108		tmp = -tmp;
109
110	return tmp;
111}
112