1/*
2 * strtod.c
3 *
4 * Convert string to double
5 *
6 * Copyright (C) 2002 Michael Ringgaard. All rights reserved.
7 * Copyright 2006-2008 H. Peter Anvin - All Rights Reserved
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the project nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    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 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
27 * 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#include <errno.h>
37#include <ctype.h>
38#include <stdlib.h>
39#include <math.h>
40
41static inline int is_real(double x)
42{
43    const double Inf = 1.0 / 0.0;
44    return (x < Inf) && (x >= -Inf);
45}
46
47double strtod(const char *str, char **endptr)
48{
49    double number;
50    int exponent;
51    int negative;
52    char *p = (char *)str;
53    double p10;
54    int n;
55    int num_digits;
56    int num_decimals;
57    const double Inf = 1.0 / 0.0;
58
59    // Skip leading whitespace
60    while (isspace(*p))
61	p++;
62
63    // Handle optional sign
64    negative = 0;
65    switch (*p) {
66    case '-':
67	negative = 1;		// Fall through to increment position
68    case '+':
69	p++;
70    }
71
72    number = 0.;
73    exponent = 0;
74    num_digits = 0;
75    num_decimals = 0;
76
77    // Process string of digits
78    while (isdigit(*p)) {
79	number = number * 10. + (*p - '0');
80	p++;
81	num_digits++;
82    }
83
84    // Process decimal part
85    if (*p == '.') {
86	p++;
87
88	while (isdigit(*p)) {
89	    number = number * 10. + (*p - '0');
90	    p++;
91	    num_digits++;
92	    num_decimals++;
93	}
94
95	exponent -= num_decimals;
96    }
97
98    if (num_digits == 0) {
99	errno = ERANGE;
100	return 0.0;
101    }
102    // Correct for sign
103    if (negative)
104	number = -number;
105
106    // Process an exponent string
107    if (*p == 'e' || *p == 'E') {
108	// Handle optional sign
109	negative = 0;
110	switch (*++p) {
111	case '-':
112	    negative = 1;	// Fall through to increment pos
113	case '+':
114	    p++;
115	}
116
117	// Process string of digits
118	n = 0;
119	while (isdigit(*p)) {
120	    n = n * 10 + (*p - '0');
121	    p++;
122	}
123
124	if (negative)
125	    exponent -= n;
126	else
127	    exponent += n;
128    }
129
130    if (exponent < __DBL_MIN_EXP__ || exponent > __DBL_MAX_EXP__) {
131	errno = ERANGE;
132	return Inf;
133    }
134    // Scale the result
135    p10 = 10.;
136    n = exponent;
137    if (n < 0)
138	n = -n;
139    while (n) {
140	if (n & 1) {
141	    if (exponent < 0)
142		number /= p10;
143	    else
144		number *= p10;
145	}
146	n >>= 1;
147	p10 *= p10;
148    }
149
150    if (!is_real(number))
151	errno = ERANGE;
152    if (endptr)
153	*endptr = p;
154
155    return number;
156}
157