Function tryParseDouble

core/3d/ObjLoader.cpp:136–259

Tries to parse a floating point number located at s. s_end should be a location in the string where reading should absolutely stop. For example at the end of the string, to prevent buffer overflows. Parses the following EBNF grammar: sign = "+" | "-" ; END = ? anything not in digit ? digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ; integer = [sign] , digit , {digit} ;

//  - parse failure.
//
static bool tryParseDouble(const char* s, const char* s_end, double* result)
{
    if (s >= s_end)
    {
        return false;
    }

    double mantissa = 0.0;
    // This exponent is base 2 rather than 10.
    // However the exponent we parse is supposed to be one of ten,
    // thus we must take care to convert the exponent/and or the
    // mantissa to a * 2^E, where a is the mantissa and E is the
    // exponent.
    // To get the final double we will use ldexp, it requires the
    // exponent to be in base 2.
    int exponent = 0;

    // NOTE: THESE MUST BE DECLARED HERE SINCE WE ARE NOT ALLOWED
    // TO JUMP OVER DEFINITIONS.
    char sign        = '+';
    char exp_sign    = '+';
    char const* curr = s;

    // How many characters were read in a loop.
    int read = 0;
    // Tells whether a loop terminated due to reaching s_end.
    bool end_not_reached = false;

    /*
     BEGIN PARSING.
     */

    // Find out what sign we've got.
    if (*curr == '+' || *curr == '-')
    {
        sign = *curr;
        curr++;
    }
    else if (isdigit(*curr))
    { /* Pass through. */
    }
    else
    {
        goto fail;
    }

    // Read the integer part.
    while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
    {
        mantissa *= 10;
        mantissa += static_cast<int>(*curr - 0x30);
        curr++;
        read++;
    }

    // We must make sure we actually got something.
    if (read == 0)
        goto fail;