digit.js
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let _boundaryCheckingState = true; // 是否进行越界检查的全局开关
/**
* 把错误的数据转正
* @private
* @example strip(0.09999999999999998)=0.1
*/
function strip(num, precision = 15) {
return +parseFloat(Number(num).toPrecision(precision));
}
/**
* Return digits length of a number
* @private
* @param {*number} num Input number
*/
function digitLength(num) {
// Get digit length of e
const eSplit = num.toString().split(/[eE]/);
const len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0);
return len > 0 ? len : 0;
}
/**
* 把小数转成整数,如果是小数则放大成整数
* @private
* @param {*number} num 输入数
*/
function float2Fixed(num) {
if (num.toString().indexOf('e') === -1) {
return Number(num.toString().replace('.', ''));
}
const dLen = digitLength(num);
return dLen > 0 ? strip(Number(num) * Math.pow(10, dLen)) : Number(num);
}
/**
* 检测数字是否越界，如果越界给出提示
* @private
* @param {*number} num 输入数
*/
function checkBoundary(num) {
if (_boundaryCheckingState) {
if (num > Number.MAX_SAFE_INTEGER || num < Number.MIN_SAFE_INTEGER) {
console.warn(`${num} 超出了精度限制，结果可能不正确`);
}
}
}
/**
* 把递归操作扁平迭代化
* @param {number[]} arr 要操作的数字数组
* @param {function} operation 迭代操作
* @private
*/
function iteratorOperation(arr, operation) {
const [num1, num2, ...others] = arr;
let res = operation(num1, num2);
others.forEach((num) => {
res = operation(res, num);
});
return res;
}
/**
* 高精度乘法
* @export
*/
export function times(...nums) {
if (nums.length > 2) {
return iteratorOperation(nums, times);
}
const [num1, num2] = nums;
const num1Changed = float2Fixed(num1);
const num2Changed = float2Fixed(num2);
const baseNum = digitLength(num1) + digitLength(num2);
const leftValue = num1Changed * num2Changed;
checkBoundary(leftValue);
return leftValue / Math.pow(10, baseNum);
}
/**
* 高精度加法
* @export
*/
export function plus(...nums) {
if (nums.length > 2) {
return iteratorOperation(nums, plus);
}
const [num1, num2] = nums;
// 取最大的小数位
const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
// 把小数都转为整数然后再计算
return (times(num1, baseNum) + times(num2, baseNum)) / baseNum;
}
/**
* 高精度减法
* @export
*/
export function minus(...nums) {
if (nums.length > 2) {
return iteratorOperation(nums, minus);
}
const [num1, num2] = nums;
const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
return (times(num1, baseNum) - times(num2, baseNum)) / baseNum;
}
/**
* 高精度除法
* @export
*/
export function divide(...nums) {
if (nums.length > 2) {
return iteratorOperation(nums, divide);
}
const [num1, num2] = nums;
const num1Changed = float2Fixed(num1);
const num2Changed = float2Fixed(num2);
checkBoundary(num1Changed);
checkBoundary(num2Changed);
// 重要，这里必须用strip进行修正
return times(num1Changed / num2Changed, strip(Math.pow(10, digitLength(num2) - digitLength(num1))));
}
/**
* 四舍五入
* @export
*/
export function round(num, ratio) {
const base = Math.pow(10, ratio);
let result = divide(Math.round(Math.abs(times(num, base))), base);
if (num < 0 && result !== 0) {
result = times(result, -1);
}
// 位数不足则补0
return result;
}
/**
* 是否进行边界检查，默认开启
* @param flag 标记开关，true 为开启，false 为关闭，默认为 true
* @export
*/
export function enableBoundaryChecking(flag = true) {
_boundaryCheckingState = flag;
}
export default {
times,
plus,
minus,
divide,
round,
enableBoundaryChecking,
};