_hdtoa.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2004-2008 David Schultz <das@FreeBSD.ORG>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <sys/cdefs.h>
30__FBSDID("$FreeBSD: stable/11/lib/libc/gdtoa/_hdtoa.c 330897 2018-03-14 03:19:51Z eadler $");
31
32#include <float.h>
33#include <limits.h>
34#include <math.h>
35
36#include "../stdio/floatio.h"
37#include "fpmath.h"
38#include "gdtoaimp.h"
39
40/* Strings values used by dtoa() */
41#define	INFSTR	"Infinity"
42#define	NANSTR	"NaN"
43
44#define	DBL_ADJ	(DBL_MAX_EXP - 2)
45#define	SIGFIGS	((DBL_MANT_DIG + 3) / 4 + 1)
46
47static const float one[] = { 1.0f, -1.0f };
48
49/*
50 * This procedure converts a double-precision number in IEEE format
51 * into a string of hexadecimal digits and an exponent of 2.  Its
52 * behavior is bug-for-bug compatible with dtoa() in mode 2, with the
53 * following exceptions:
54 *
55 * - An ndigits < 0 causes it to use as many digits as necessary to
56 *   represent the number exactly.
57 * - The additional xdigs argument should point to either the string
58 *   "0123456789ABCDEF" or the string "0123456789abcdef", depending on
59 *   which case is desired.
60 * - This routine does not repeat dtoa's mistake of setting decpt
61 *   to 9999 in the case of an infinity or NaN.  INT_MAX is used
62 *   for this purpose instead.
63 *
64 * Note that the C99 standard does not specify what the leading digit
65 * should be for non-zero numbers.  For instance, 0x1.3p3 is the same
66 * as 0x2.6p2 is the same as 0x4.cp3.  This implementation always makes
67 * the leading digit a 1. This ensures that the exponent printed is the
68 * actual base-2 exponent, i.e., ilogb(d).
69 *
70 * Inputs:	d, xdigs, ndigits
71 * Outputs:	decpt, sign, rve
72 */
73char *
74__hdtoa(double d, const char *xdigs, int ndigits, int *decpt, int *sign,
75    char **rve)
76{
77	union IEEEd2bits u;
78	char *s, *s0;
79	int bufsize;
80	uint32_t manh, manl;
81
82	u.d = d;
83	*sign = u.bits.sign;
84
85	switch (fpclassify(d)) {
86	case FP_NORMAL:
87		*decpt = u.bits.exp - DBL_ADJ;
88		break;
89	case FP_ZERO:
90		*decpt = 1;
91		return (nrv_alloc("0", rve, 1));
92	case FP_SUBNORMAL:
93		u.d *= 0x1p514;
94		*decpt = u.bits.exp - (514 + DBL_ADJ);
95		break;
96	case FP_INFINITE:
97		*decpt = INT_MAX;
98		return (nrv_alloc(INFSTR, rve, sizeof(INFSTR) - 1));
99	default:	/* FP_NAN or unrecognized */
100		*decpt = INT_MAX;
101		return (nrv_alloc(NANSTR, rve, sizeof(NANSTR) - 1));
102	}
103
104	/* FP_NORMAL or FP_SUBNORMAL */
105
106	if (ndigits == 0)		/* dtoa() compatibility */
107		ndigits = 1;
108
109	/*
110	 * If ndigits < 0, we are expected to auto-size, so we allocate
111	 * enough space for all the digits.
112	 */
113	bufsize = (ndigits > 0) ? ndigits : SIGFIGS;
114	s0 = rv_alloc(bufsize);
115
116	/* Round to the desired number of digits. */
117	if (SIGFIGS > ndigits && ndigits > 0) {
118		float redux = one[u.bits.sign];
119		int offset = 4 * ndigits + DBL_MAX_EXP - 4 - DBL_MANT_DIG;
120		u.bits.exp = offset;
121		u.d += redux;
122		u.d -= redux;
123		*decpt += u.bits.exp - offset;
124	}
125
126	manh = u.bits.manh;
127	manl = u.bits.manl;
128	*s0 = '1';
129	for (s = s0 + 1; s < s0 + bufsize; s++) {
130		*s = xdigs[(manh >> (DBL_MANH_SIZE - 4)) & 0xf];
131		manh = (manh << 4) | (manl >> (DBL_MANL_SIZE - 4));
132		manl <<= 4;
133	}
134
135	/* If ndigits < 0, we are expected to auto-size the precision. */
136	if (ndigits < 0) {
137		for (ndigits = SIGFIGS; s0[ndigits - 1] == '0'; ndigits--)
138			;
139	}
140
141	s = s0 + ndigits;
142	*s = '\0';
143	if (rve != NULL)
144		*rve = s;
145	return (s0);
146}
147