157 lines
3.6 KiB
C
157 lines
3.6 KiB
C
/*
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* strtod.c
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*
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* Convert string to double
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*
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* Copyright (C) 2002 Michael Ringgaard. All rights reserved.
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* Copyright 2006-2008 H. Peter Anvin - All Rights Reserved
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the project nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <errno.h>
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#include <ctype.h>
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#include <stdlib.h>
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#include <math.h>
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static inline int is_real(double x)
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{
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const double Inf = 1.0 / 0.0;
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return (x < Inf) && (x >= -Inf);
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}
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double strtod(const char *str, char **endptr)
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{
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double number;
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int exponent;
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int negative;
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char *p = (char *)str;
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double p10;
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int n;
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int num_digits;
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int num_decimals;
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const double Inf = 1.0 / 0.0;
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// Skip leading whitespace
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while (isspace(*p))
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p++;
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// Handle optional sign
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negative = 0;
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switch (*p) {
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case '-':
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negative = 1; // Fall through to increment position
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case '+':
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p++;
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}
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number = 0.;
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exponent = 0;
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num_digits = 0;
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num_decimals = 0;
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// Process string of digits
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while (isdigit(*p)) {
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number = number * 10. + (*p - '0');
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p++;
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num_digits++;
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}
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// Process decimal part
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if (*p == '.') {
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p++;
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while (isdigit(*p)) {
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number = number * 10. + (*p - '0');
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p++;
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num_digits++;
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num_decimals++;
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}
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exponent -= num_decimals;
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}
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if (num_digits == 0) {
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errno = ERANGE;
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return 0.0;
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}
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// Correct for sign
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if (negative)
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number = -number;
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// Process an exponent string
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if (*p == 'e' || *p == 'E') {
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// Handle optional sign
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negative = 0;
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switch (*++p) {
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case '-':
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negative = 1; // Fall through to increment pos
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case '+':
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p++;
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}
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// Process string of digits
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n = 0;
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while (isdigit(*p)) {
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n = n * 10 + (*p - '0');
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p++;
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}
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if (negative)
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exponent -= n;
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else
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exponent += n;
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}
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if (exponent < __DBL_MIN_EXP__ || exponent > __DBL_MAX_EXP__) {
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errno = ERANGE;
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return Inf;
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}
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// Scale the result
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p10 = 10.;
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n = exponent;
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if (n < 0)
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n = -n;
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while (n) {
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if (n & 1) {
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if (exponent < 0)
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number /= p10;
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else
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number *= p10;
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}
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n >>= 1;
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p10 *= p10;
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}
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if (!is_real(number))
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errno = ERANGE;
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if (endptr)
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*endptr = p;
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return number;
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}
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