BigDecimal#precision

static VALUE
BigDecimal_precision(VALUE self)
{
    ENTER(1);

    Real *p;
    GUARD_OBJ(p, GetVpValue(self, 1));

    /*
     * The most significant digit is frac[0], and the least significant digit is frac[Prec-1].
     * When the exponent is zero, the decimal point is located just before frac[0].
     * When the exponent is negative, the decimal point moves to leftward.
     * Conversely, when the exponent is positive, the decimal point moves to rightward.
     *
     *    | frac[0] frac[1] frac[2] . frac[3] frac[4] ... frac[Prec-1]
     *    |------------------------> exponent == 3
     */

    ssize_t ex = p->exponent;
    ssize_t precision = 0;
    if (ex < 0) {
        precision = (-ex + 1) * BASE_FIG;  /* 1 is for p->frac[0] */
        ex = 0;
    }
    else if (p->Prec > 0) {
        BDIGIT x = p->frac[0];
        for (precision = 0; x > 0; x /= 10) {
            ++precision;
        }
    }

    if (ex > (ssize_t)p->Prec) {
        precision += (ex - 1) * BASE_FIG;
    }
    else if (p->Prec > 0) {
        ssize_t n = (ssize_t)p->Prec - 1;
        while (n > 0 && p->frac[n] == 0) --n;

        precision += n * BASE_FIG;

        if (ex < (ssize_t)p->Prec) {
            BDIGIT x = p->frac[n];
            for (; x > 0 && x % 10 == 0; x /= 10) {
                --precision;
            }
        }
    }

    return SSIZET2NUM(precision);
}