luckysheet/src/utils/math.js

import { isRealNum } from '../global/validate';

/*
 * 判断obj是否为一个整数
 */
function isInteger(obj) {
    return Math.floor(obj) === obj;
}

/*
 * 将一个浮点数转成整数，返回整数和倍数。如 3.14 >> 314，倍数是 100
 * @param floatNum {number} 小数
 * @return {object}
 *   {times:100, num: 314}
 */
function toInteger(floatNum) {
    var ret = { times: 1, num: 0 };

    if (isInteger(floatNum)) {
        ret.num = floatNum;
        return ret;
    }

    var strfi = floatNum + '';
    var dotPos = strfi.indexOf('.');
    var len = strfi.substr(dotPos + 1).length;
    var times = Math.pow(10, len);
    var intNum = parseInt(floatNum * times + 0.5, 10);

    ret.times = times;
    ret.num = intNum;

    return ret;
}

/*
 * 核心方法，实现加减乘除运算，确保不丢失精度
 * 思路：把小数放大为整数（乘），进行算术运算，再缩小为小数（除）
 *
 * @param a {number} 运算数1
 * @param b {number} 运算数2
 * @param digits {number} 精度，保留的小数点数，比如 2, 即保留为两位小数
 * @param op {string} 运算类型，有加减乘除（add/subtract/multiply/divide）
 *
 */
function operation(a, b, op) {
    var o1 = toInteger(a);
    var o2 = toInteger(b);
    var n1 = o1.num;
    var n2 = o2.num;
    var t1 = o1.times;
    var t2 = o2.times;
    var max = t1 > t2 ? t1 : t2;
    var result = null;

    switch (op) {
        case 'add':
            if (t1 === t2) { // 两个小数位数相同
                result = n1 + n2;
            }
            else if (t1 > t2) { // o1 小数位 大于 o2
                result = n1 + n2 * (t1 / t2);
            }
            else { // o1 小数位 小于 o2
                result = n1 * (t2 / t1) + n2;
            }

            return result / max;
        case 'subtract':
            if (t1 === t2) {
                result = n1 - n2;
            }
            else if (t1 > t2) {
                result = n1 - n2 * (t1 / t2);
            }
            else {
                result = n1 * (t2 / t1) - n2;
            }

            return result / max;
        case 'multiply':
            result = (n1 * n2) / (t1 * t2);

            return result;
        case 'divide':
            return result = function () {
                var r1 = n1 / n2;
                var r2 = t2 / t1;
                return operation(r1, r2, 'multiply');
            }();
    }
}
/**
 * 做小数点的四舍五入计算
 * @param {*} num
 * @param {*} precision
 */
function fixed(num, precision) {
    if (!precision) {
        precision = 2;
    }
    if (!isRealNum(num)) return num;
    let s = num.toFixed(precision);
    let index = s.indexOf('.');
    let prefix = s.substring(0, index);
    let suffix = s.substring(index + 1, s.length);
    if (suffix) {
        for (let i = suffix.length - 1; i != 0; i--) {
            //最末位不为0，直接break;
            if (suffix.charAt(i) != '0' && i == suffix.length - 1) {
                break;
            } else {
                suffix = suffix.substring(0, i);
            }
        }
    }
    return Number(prefix + '.' + suffix);
}


/**
 * Calculation +-/* Solve the problem of js accuracy
 */
Number.prototype.add = function (value) {
    let  number = parseFloat(value);
    if (typeof number !== 'number' || Number.isNaN(number)) {
        throw new Error('请输入数字或者数字字符串～');
    };
    return operation(this, number, 'add');
};
Number.prototype.subtract = function (value) {
    let  number = parseFloat(value);
    if (typeof number !== 'number' || Number.isNaN(number)) {
        throw new Error('请输入数字或者数字字符串～');
    }
    return operation(this, number, 'subtract');
};
Number.prototype.multiply = function (value) {
    let  number = parseFloat(value);
    if (typeof number !== 'number' || Number.isNaN(number)) {
        throw new Error('请输入数字或者数字字符串～');
    }
    return operation(this, number, 'multiply');
};
Number.prototype.divide = function (value) {
    let  number = parseFloat(value);
    if (typeof number !== 'number' || Number.isNaN(number)) {
        throw new Error('请输入数字或者数字字符串～');
    }
    return operation(this, number, 'divide');
};
Number.prototype.tofixed = function (value) {
    let  precision = parseFloat(value);
    if (typeof precision !== 'number' || Number.isNaN(precision)) {
        throw new Error('请输入数字或者数字字符串～');
    }
    return fixed(this, precision);
};