source: bootcd/isolinux/syslinux-6.03/com32/lib/math/strtod.c @ 26ffad7

/*
 * strtod.c
 *
 * Convert string to double
 *
 * Copyright (C) 2002 Michael Ringgaard. All rights reserved.
 * Copyright 2006-2008 H. Peter Anvin - All Rights Reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <errno.h>
#include <ctype.h>
#include <stdlib.h>
#include <math.h>

static inline int is_real(double x)
{
    const double Inf = 1.0 / 0.0;
    return (x < Inf) && (x >= -Inf);
}

double strtod(const char *str, char **endptr)
{
    double number;
    int exponent;
    int negative;
    char *p = (char *)str;
    double p10;
    int n;
    int num_digits;
    int num_decimals;
    const double Inf = 1.0 / 0.0;

    // Skip leading whitespace
    while (isspace(*p))
        p++;

    // Handle optional sign
    negative = 0;
    switch (*p) {
    case '-':
        negative = 1;           // Fall through to increment position
    case '+':
        p++;
    }

    number = 0.;
    exponent = 0;
    num_digits = 0;
    num_decimals = 0;

    // Process string of digits
    while (isdigit(*p)) {
        number = number * 10. + (*p - '0');
        p++;
        num_digits++;
    }

    // Process decimal part
    if (*p == '.') {
        p++;

        while (isdigit(*p)) {
            number = number * 10. + (*p - '0');
            p++;
            num_digits++;
            num_decimals++;
        }

        exponent -= num_decimals;
    }

    if (num_digits == 0) {
        errno = ERANGE;
        return 0.0;
    }
    // Correct for sign
    if (negative)
        number = -number;

    // Process an exponent string
    if (*p == 'e' || *p == 'E') {
        // Handle optional sign
        negative = 0;
        switch (*++p) {
        case '-':
            negative = 1;       // Fall through to increment pos
        case '+':
            p++;
        }

        // Process string of digits
        n = 0;
        while (isdigit(*p)) {
            n = n * 10 + (*p - '0');
            p++;
        }

        if (negative)
            exponent -= n;
        else
            exponent += n;
    }

    if (exponent < __DBL_MIN_EXP__ || exponent > __DBL_MAX_EXP__) {
        errno = ERANGE;
        return Inf;
    }
    // Scale the result
    p10 = 10.;
    n = exponent;
    if (n < 0)
        n = -n;
    while (n) {
        if (n & 1) {
            if (exponent < 0)
                number /= p10;
            else
                number *= p10;
        }
        n >>= 1;
        p10 *= p10;
    }

    if (!is_real(number))
        errno = ERANGE;
    if (endptr)
        *endptr = p;

    return number;
}