kf.js

'use strict';

const _JINGDU = 1e-6

function judgeZero(tag) {
    return Math.abs(tag) <= _JINGDU
}

// 暴力开平方
function baoliSqrt(num) {
    console.time("Baoli SQRT")
    var i
    for (i = 0; Math.abs(num - i * i) > _JINGDU; i += _JINGDU);
    console.log(i)
    console.timeEnd("Baoli SQRT")
}

// 原生库函数开平方
function localSqrt(num) {
    console.time('Local SQRT')
    var i = Math.sqrt(num)
    console.log('Local SQRT:', i)
    console.timeEnd('Local SQRT')
}

// 牛顿开平方
function newtonSqrt(num) {
    console.time("Newton SQRT")
    var _avg = num
    var last_avg = 0

    while (Math.abs(_avg - last_avg) > _JINGDU) {
        last_avg = _avg
        _avg = (_avg + num / _avg) / 2
    }
    console.log("Newton SQRT:", _avg)
    console.timeEnd("Newton SQRT")
}

// 暴力加牛顿开方
function baoliAndNewtonSqrt(num) {
    console.time('BaoliAndNewton SQRT')
    var _avg, i = 0,
        last_avg = 0
    for (i = 0; i * i < num; i += 0.1);
    _avg = i;

    while (Math.abs(_avg - last_avg) > _JINGDU) {
        last_avg = _avg;
        _avg = (_avg + num / _avg) / 2;
    }
    console.log('BaoliAndNewton SQRT:', _avg)
    console.timeEnd('BaoliAndNewton SQRT')
}

// 二分法开方
function erfenSqrt(num) {
    console.time('Erfen SQRT')
    var _low = 0,
        _high = num,
        _mid = 9999999,
        last_mid = 0

    while (Math.abs(_mid - last_mid) > _JINGDU) {
        last_mid = _mid;
        _mid = (_low + _high) / 2;
        if (_mid * _mid > num)
            _high = _mid;
        if (_mid * _mid < num)
            _low = _mid;

    }
    console.log('Erfen SQRT:', _mid)
    console.timeEnd('Erfen SQRT')
}

// function invSqrt(num) {
//     float xhalf = 0.5f* num
//     int i = *(int *)& num // get bits for floating VALUE  
//     i = 0x5f375a86 - (i >> 1); // gives initial guess y0  
//     x = *(float *)& i; // convert bits BACK to float  
//     x = x * (1.5f- xhalf * x * x); // Newton step, repeating increases accuracy  
//     return x;
// }