groovy中默认的bigdecimal标度

5.5.1. The case of the division operator

The division operators / (and /= for division and assignment) produce
a double result if either operand is a float or double,and a
BigDecimal result otherwise (when both operands are any combination of
an integral type short,char,byte,int,long,BigInteger or
BigDecimal).

BigDecimal division is performed with the divide() method if the
division is exact (i.e. yielding a result that can be represented
within the bounds of the same precision and scale),or using a
MathContext with a precision of the maximum of the two operands’
precision plus an extra precision of 10,and a scale of the maximum of
10 and the maximum of the operands’ scale.

并在BigDecimalMath.java检查：

public Number divideImpl(Number left,Number right) {
    BigDecimal bigLeft = toBigDecimal(left);
    BigDecimal bigRight = toBigDecimal(right);
    try {
        return bigLeft.divide(bigRight);
    } catch (ArithmeticException e) {
        // set a DEFAULT precision if otherwise non-terminating
        int precision = Math.max(bigLeft.precision(),bigRight.precision()) + DIVISION_EXTRA_PRECISION;
        BigDecimal result = bigLeft.divide(bigRight,new MathContext(precision));
        int scale = Math.max(Math.max(bigLeft.scale(),bigRight.scale()),DIVISION_MIN_SCALE);
        if (result.scale() > scale) result = result.setScale(scale,BigDecimal.ROUND_HALF_UP);
        return result;
    }
}