浮点数的舍入误差

/**
 * @param n Number to be rounded.
 * @param precision Decimal places.
 * @return Rounded Number
 */
function roundDecimal(n:Number, precision:Number):Number {
    var factor:int = Math.pow(10, precision);
    return (Math.round(n * factor) / factor);
}

例子：

trace(0.9 - 1); // -0.09999999999999998

trace(roundDecimal(0.9 - 1, 1));     // -0.1
trace(roundDecimal(0.9 - 1, 2));     // -0.1

trace(roundDecimal(0.9 - 1.123, 1)); // -0.2
trace(roundDecimal(0.9 - 1.123, 2)); // -0.22
trace(roundDecimal(0.9 - 1.123, 3)); // -0.223