1 /*
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright © 2022 Keith Packard
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 *
13 * 2. Redistributions in binary form must reproduce the above
14 * copyright notice, this list of conditions and the following
15 * disclaimer in the documentation and/or other materials provided
16 * with the distribution.
17 *
18 * 3. Neither the name of the copyright holder nor the names of its
19 * contributors may be used to endorse or promote products derived
20 * from this software without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
23 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
24 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
25 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
26 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
27 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
28 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
29 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
31 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
32 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
33 * OF THE POSSIBILITY OF SUCH DAMAGE.
34 */
35
36 #define _GNU_SOURCE
37 #include "dtoa_engine.h"
38 #include <_ansi.h>
39 #include <stdlib.h>
40 #include <string.h>
41 #include <math.h>
42
43 int
fcvt_r(double invalue,int ndecimal,int * decpt,int * sign,char * buf,size_t len)44 fcvt_r (double invalue,
45 int ndecimal,
46 int *decpt,
47 int *sign,
48 char *buf,
49 size_t len)
50 {
51 struct dtoa dtoa;
52 int ntrailing; /* number of zeros to add after the value */
53 int ndigit; /* numer of generated digits */
54 int dtoa_decimal = ndecimal;
55 char *digits = dtoa.digits;
56
57 if (!isfinite(invalue)) {
58 ndigit = 3;
59 ntrailing = 0;
60 *sign = invalue < 0;
61 *decpt = 0;
62 if (isnan(invalue))
63 digits = "nan";
64 else
65 digits = "inf";
66 } else {
67 /* ndecimal = digits after decimal point desired
68 * ndigit = digits actually generated
69 * dtoa.exp = exponent (position of decimal relative to first digit generated)
70 */
71 if (ndecimal < 0)
72 dtoa_decimal = 0;
73 ndigit = __dtoa_engine(invalue, &dtoa, DTOA_MAX_DIG, true, ndecimal);
74 *sign = !!(dtoa.flags & DTOA_MINUS);
75
76 /*
77 * To compute the number of zeros added after the value, there are
78 * three cases:
79 *
80 * 1. all of the generated digits are left of the decimal
81 * point (dtoa.exp >= ndigit). We need (dtoa.exp - ndigit)
82 * digits left of the decimal and ndecimal right of the
83 * decimal: (dtoa.exp - ndigit) + ndecimal
84 *
85 * 2. some of the generated digits are right
86 * of the decimal point (dtoa.exp < ndigit). We need
87 * ndecimal digits total, but we have (ndigit - dtoa.exp)
88 * already, so: ndecimal - (ndigit - dtoa.exp).
89 *
90 * 3. all of the generated digits are right of the decimal point
91 * We need fewer than ndecimal digits by the magnitude of
92 * the exponent (which is negative in this case, so:
93 * ndecimal - (-dtoa.exp - 1) - ndigit
94 *
95 * These all turn out to be the same computation. Kinda cool.
96 */
97 ntrailing = (dtoa.exp + 1 - ndigit) + dtoa_decimal;
98 /*
99 * If this value is negative, then we actually have *no* digits to
100 * generate. In this case, we return the empty string and set the
101 * exponent to the number of digits requested (as they're all
102 * zero)
103 */
104 if (ntrailing < 0) {
105 ntrailing = 0;
106 ndigit = 0;
107
108 /*
109 * Adjust exponent to reflect the desired output of ndecimal
110 * zeros
111 */
112 dtoa.exp = -(dtoa_decimal + 1);
113 }
114 *decpt = dtoa.exp + 1;
115 }
116
117 /* If we can't fit the whole value in the provided space,
118 * return an error
119 */
120 if ((size_t) (ndigit + ntrailing) >= len)
121 return -1;
122
123 /* Value */
124 memcpy(buf, digits, ndigit);
125 len -= ndigit;
126 buf += ndigit;
127
128 /* Trailing zeros */
129 memset(buf, '0', ntrailing);
130 buf += ntrailing;
131
132 /* Null terminate */
133 buf[0] = '\0';
134 return 0;
135 }
136
