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