153 lines
4.5 KiB
JavaScript
153 lines
4.5 KiB
JavaScript
/**
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* @desc 解决浮动运算问题，避免小数点后产生多位数和计算精度损失。
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*
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* 问题示例：2.3 + 2.4 = 4.699999999999999，1.0 - 0.9 = 0.09999999999999998
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*/
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/**
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* Correct the given number to specifying significant digits.
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*
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* @param num The input number
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* @param precision An integer specifying the number of significant digits
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*
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* @example strip(0.09999999999999998) === 0.1 // true
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*/
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function strip(num, precision) {
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if (precision === void 0) { precision = 15; }
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return +parseFloat(Number(num).toPrecision(precision));
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}
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/**
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* Return digits length of a number.
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*
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* @param num The input number
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*/
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function digitLength(num) {
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// Get digit length of e
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var eSplit = num.toString().split(/[eE]/);
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var len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0);
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return len > 0 ? len : 0;
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}
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/**
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* Convert the given number to integer, support scientific notation.
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* The number will be scale up if it is decimal.
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*
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* @param num The input number
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*/
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function float2Fixed(num) {
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if (num.toString().indexOf('e') === -1) {
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return Number(num.toString().replace('.', ''));
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}
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var dLen = digitLength(num);
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return dLen > 0 ? strip(Number(num) * Math.pow(10, dLen)) : Number(num);
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}
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/**
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* Log a warning if the given number is out of bounds.
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*
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* @param num The input number
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*/
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function checkBoundary(num) {
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if (_boundaryCheckingState) {
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if (num > Number.MAX_SAFE_INTEGER || num < Number.MIN_SAFE_INTEGER) {
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console.warn(num + " is beyond boundary when transfer to integer, the results may not be accurate");
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}
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}
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}
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/**
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* Create an operation to support rest params.
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*
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* @param operation The original operation
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*/
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function createOperation(operation) {
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return function () {
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var nums = [];
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for (var _i = 0; _i < arguments.length; _i++) {
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nums[_i] = arguments[_i];
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}
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var first = nums[0], others = nums.slice(1);
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return others.reduce(function (prev, next) { return operation(prev, next); }, first);
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};
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}
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/**
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* Accurate multiplication.
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*
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* @param nums The numbers to multiply
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*/
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var times = createOperation(function (num1, num2) {
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var num1Changed = float2Fixed(num1);
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var num2Changed = float2Fixed(num2);
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var baseNum = digitLength(num1) + digitLength(num2);
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var leftValue = num1Changed * num2Changed;
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checkBoundary(leftValue);
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return leftValue / Math.pow(10, baseNum);
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});
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/**
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* Accurate addition.
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*
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* @param nums The numbers to add
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*/
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var plus = createOperation(function (num1, num2) {
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// 取最大的小数位
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var baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
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// 把小数都转为整数然后再计算
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return (times(num1, baseNum) + times(num2, baseNum)) / baseNum;
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});
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/**
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* Accurate subtraction.
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*
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* @param nums The numbers to subtract
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*/
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var minus = createOperation(function (num1, num2) {
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var baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
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return (times(num1, baseNum) - times(num2, baseNum)) / baseNum;
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});
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/**
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* Accurate division.
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*
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* @param nums The numbers to divide
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*/
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var divide = createOperation(function (num1, num2) {
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var num1Changed = float2Fixed(num1);
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var num2Changed = float2Fixed(num2);
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checkBoundary(num1Changed);
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checkBoundary(num2Changed);
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// fix: 类似 10 ** -4 为 0.00009999999999999999，strip 修正
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return times(num1Changed / num2Changed, strip(Math.pow(10, digitLength(num2) - digitLength(num1))));
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});
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/**
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* Accurate rounding method.
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*
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* @param num The number to round
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* @param decimal An integer specifying the decimal digits
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*/
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function round(num, decimal) {
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var base = Math.pow(10, decimal);
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var result = divide(Math.round(Math.abs(times(num, base))), base);
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if (num < 0 && result !== 0) {
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result = times(result, -1);
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}
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return result;
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}
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var _boundaryCheckingState = true;
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/**
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* Whether to check the bounds of number, default is enabled.
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*
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* @param flag The value to indicate whether is enabled
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*/
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function enableBoundaryChecking(flag) {
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if (flag === void 0) { flag = true; }
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_boundaryCheckingState = flag;
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}
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var index = {
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strip: strip,
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plus: plus,
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minus: minus,
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times: times,
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divide: divide,
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round: round,
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digitLength: digitLength,
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float2Fixed: float2Fixed,
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enableBoundaryChecking: enableBoundaryChecking,
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};
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export { strip, plus, minus, times, divide, round, digitLength, float2Fixed, enableBoundaryChecking };
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export default index;
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