Function step_round

src/backend/common/graphics_common.cpp:187–240

dir -> true = round up, false = round down

// dir -> true = round up, false = round down
double step_round(const double in, const bool dir) {
    if (in == 0) { return 0; }

    static const double LOG2 = log10(2);
    static const double LOG4 = log10(4);
    static const double LOG6 = log10(6);
    static const double LOG8 = log10(8);

    // log_in is of the form "s abc.xyz", where
    // s is either + or -; + indicates abs(in) >= 1 and - indicates 0 < abs(in)
    // < 1 (log10(1) is +0)
    const double sign   = in < 0 ? -1 : 1;
    const double log_in = std::log10(std::fabs(in));
    const double mag    = std::pow(10, std::floor(log_in)) *
                       sign;  // Number of digits either left or right of 0
    const double dec = std::log10(in / mag);  // log of the fraction

    // This means in is of the for 10^n
    if (dec == 0) { return in; }

    // For negative numbers, -ve round down = +ve round up and vice versa
    bool op_dir = in > 0 ? dir : !dir;

    double mult = 1;

    // Round up
    if (op_dir) {
        if (dec <= LOG2) {
            mult = 2;
        } else if (dec <= LOG4) {
            mult = 4;
        } else if (dec <= LOG6) {
            mult = 6;
        } else if (dec <= LOG8) {
            mult = 8;
        } else {
            mult = 10;
        }
    } else {  // Round down
        if (dec < LOG2) {
            mult = 1;
        } else if (dec < LOG4) {
            mult = 2;
        } else if (dec < LOG6) {
            mult = 4;
        } else if (dec < LOG8) {
            mult = 6;
        } else {
            mult = 8;
        }
    }

    return mag * mult;
}

ForgeModule& forgePlugin() { return detail::forgeManager().plugin(); }