Question

Java的toPrecision约等于四舍五入

(123.46).toPrecision(4)    // 123.5
(123.44).toPrecision(4)    // 123.4

但是，选择舍入方向（上/下或下/下）的简单方法是什么？所以

(123.46).toPrecisionFloor(4)   // would give 123.4
(123.44).toPrecisionCeil(4)    // 123.5

Answer 1

这不是一个班轮，但我认为这符合您的要求？您可能可以整理一下。

编辑（以一种非常基本的方式）进行了更新，可以处理有效数字而不是小数

编辑2 稍微弄清代码并添加了进一步的测试

/**
 * rounds a number up or down to specified accuracy
 * @param number {numeric} number to perform operations on
 * @param precision {numeric} number of significant figures to return
 * @param direction {string} wether to round up or down
 */
function toPrecision(number, precision, direction) {
  precision -= Math.floor(number).toString().length;
  var order = Math.pow(10, precision);
  number *= order;
  var option = (direction === 'down' ? 'floor' : 'ceil');
  return (Math[option].call(null, number) / order);
}

// values to test
var test_1 = 123.567891;
var test_2 = 15000;
var test_3 = 12340000;

// define tests
var tests = {
  "a": [test_1, 3, "down"],
  "b": [test_1, 4, "up"],
  "c": [test_2, 3, "down"],
  "d": [test_2, 4, "up"],
  "e": [test_2, 1, "down"],
  "f": [test_2, 1, "up"],
  "g": [test_3, 4, "down"],
  "h": [test_3, 4, "up"]
}

// loop over tests and execute
for (var key in tests) {
  console.log("key:", key, "result: ", toPrecision.apply(null, tests[key]));
}

/*
	Test results: 
  key: a result:  123
  key: b result:  123.6
  key: c result:  15000
  key: d result:  15000
  key: e result:  10000
  key: f result:  20000
  key: g result:  12340000
  key: h result:  12340000
*/

JS Fiddle link

到精确的舍入方向

1 个答案: