好玩的.进位加、乘法

版权声明：个人笔记，不喜勿喷 https://blog.csdn.net/qq_39571197/article/details/88684156

// utils.js
module.exports = {
    isFloat(...numOrStrs) {
        const POINT_REG = /\./;
        return !!numOrStrs.find(item => POINT_REG.test(item));
    },
    fixLen(a, b, isRight0 = true) {
        a += '', b += '';
        let diff = a.length - b.length;
        const fixStr = '0'.repeat(Math.abs(diff));
        if (diff === 0) {
            return [a, b];
        }
        if (isRight0) {
            if (diff < 0) {
                // b 长
                return [fixStr + a, b];
            } else {
                // a 长
                return [a, fixStr + b];
            }

        } else {
            if (diff < 0) {
                // b 长
                return [a + fixStr, b];
            } else {
                // a 长
                return [a, b + fixStr];
            }
        }

    },
    transToInt(num) {
        num += '';
        const pointIndex = num.indexOf('.');
        const diff = num.length - 1 - pointIndex;
        return {
            move: diff,
            value: num.replace(/\./, ''),
        };
    },
};

// 加法
const utils = require('./utils');
module.exports = add;
function add(a, b) {
    a += '', b += '';
    const isFloatMode = utils.isFloat(a, b);
    if (!isFloatMode) {
        return $add(a, b) * 1;
    }
    // 浮点数运算
    const [intA, floatA] = a.split('.');
    const [intB, floatB] = b.split('.');
    let intResult = $add(intA, intB);
    let floatResult = $add(floatA, floatB, false);
    // 处理小数
    const floatLenDiff = floatResult.length - Math.max(floatA.length, floatB.length);
    if (floatLenDiff > 0) {
        const _int = floatResult.slice(0, floatLenDiff), _float = floatResult.slice(floatLenDiff);
        intResult = $add(intResult, _int);
        floatResult = _float;
    }
    return (intResult + '.' + floatResult) * 1;
}
console.log(add(646.5541, 554.6469)); // 1201.201
console.log(add(0.1, 0.2)); // 0.3
console.log(add(15, 25)); // 40

function $add(a, b, isRight0 = true) {
    [a, b] = utils.fixLen(a, b, isRight0);
    let result = '';
    let carryNum = 0;
    for (let i = a.length - 1; i >= 0; i--) {
        let _r = a[i] * 1 + b[i] * 1 + carryNum;
        if (_r >= 10) {
            carryNum = 1;
            _r -= 10;
        } else {
            carryNum = 0;
        }
        result = _r + result;
    }
    if (carryNum === 1) {
        result = '1' + result;
    }
    return result;
}

// 乘法
const utils = require('./utils');
const add = require('./add');
console.log(1)
function time(a, b) {
    a += '', b += '';
    let intRate = 1; // 放大倍率
    if (utils.isFloat(a)) {
        const info = utils.transToInt(a);
        a = info.value;
        intRate *= Math.pow(10, info.move);
    }
    if (utils.isFloat(b)) {
        const info = utils.transToInt(b);
        b = info.value;
        intRate *= Math.pow(10, info.move);
    }
    let results = [];
    let post = 0;
    for (let i = b.length - 1; i >= 0; i-- , post++) {
        results.push(singleTime(a, b[i]) + '0'.repeat(post));
    }
    let result = 0;
    for (let i = 0; i < results.length; i++) {
        result = add(result, results[i]);
    }
    return result / intRate;
}
console.log(time(199.9, 90.5)); // 18090.95
console.log(time(31231.00219, 515.55)); // 16101143.1790545
function singleTime(a, cur) {
    let result = '';
    let carryNum = 0;
    for (let i = a.length - 1; i >= 0; i--) {
        let _r = a[i] * cur + carryNum;
        if (_r >= 10) {
            carryNum = Math.floor(_r / 10);
            _r %= 10;
        } else {
            carryNum = 0;
        }
        result = _r + result;
    }
    if (carryNum > 0) {
        result = carryNum + result;
    }
    return result;
}