js 进制转换

  最近想对js中的数字进行压缩, 百度了一下, 发现相关结果很少, 比如:

//var base_symbols = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz~`!@#$%^&*()-_=+[{]}\\\\|;:'",<.>/?????";
  var base_symbols = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz~`!@#$%^&*()-_=+[{]}\\|;:'\",<.>/?¿¡";

function baseConvert(src, from_base, to_base, src_symbol_table, dest_symbol_table) {
    // From: convert.js: http://rot47.net/_js/convert.js
    // Modified by MLM to work with BigInteger: https://github.com/peterolson/BigInteger.js

    src_symbol_table = src_symbol_table ? src_symbol_table : base_symbols;
    dest_symbol_table = dest_symbol_table ? dest_symbol_table : src_symbol_table;

    if(from_base > src_symbol_table.length || to_base > dest_symbol_table.length) {
        console.warn("Can't convert", src,"to base", to_base,"greater than symbol table length. src-table:", src_symbol_table.length,"dest-table:", dest_symbol_table.length);
        return false;
    }

    var val = bigInt(0);
    for(var i = 0; i < src.length; i ++) {
        val = val.multiply(from_base).add(src_symbol_table.indexOf(src.charAt(i)));
    }
    if(val.lesser(0)) {
        return 0;
    }

    var r = val.mod(to_base);
    var res = dest_symbol_table.charAt(r);
    var q = val.divide(to_base);
    while(!q.equals(0)) {
        r = q.mod(to_base);
        q = q.divide(to_base);
        res = dest_symbol_table.charAt(r) + res;
    }

    return res;
}

但由于缺少BigInteger.js支持, 此段代码无法使用. 于是, 结合网友的点子, 一段新的代码诞生了!
十进制转N进制:

if(!diyBase.dftBase) {
    /**
     * [A-Z]字符集
     * @type {string}
     */
    diyBase.dftBase = (function(f,t){var i=f,c='';while(i<=t){c+=String.fromCharCode(i++)}return c;})(65,90)
}
/**
 * 自定义进制
 * @param {number} n 自然数
 * @param charset 进制字符集. 默认[A-Z]
 * @param hasZero 进制是否含0. 默认不含, 与charset对应
 * @example
 * // 十六进制
 * diyBase(10, '0123456789ABCDEF', true) // return 'A'
 * diyBase(255, '0123456789ABCDEF', true) // return 'FF'
 * // excel 中的列
 * diyBase(25) // return 'Z'
 * diyBase(26) // return 'AA'
 * @return {string} 返回值
 */
function diyBase(n, charset, hasZero) {
    charset = charset||diyBase.dftBase;
    hasZero = hasZero!==undefined?!!hasZero:false;
    if(n < charset.length){
        return charset.substr(n, 1);
    }
    // 递归个位以上的部分
    var high = Math.floor(n / charset.length);
    var unit = n % charset.length;
    return diyBase(high - (1^hasZero), charset, hasZero) + charset.substr(unit, 1);
}

N进制转十进制:

/**
 * @example
 * diyBaseDecode('A', '0123456789ABCDEF', true) // returns 10
 * diyBaseDecode('FF', '0123456789ABCDEF', true) // returns 255
 * diyBaseDecode('Z') // returns 25
 * diyBaseDecode('AA') // returns 26
 * @param {string} c
 * @param {string} charset
 * @param {boolean} [hasZero]
 * @returns {number}
 */
function diyBaseDecode(c, charset, hasZero) {
    charset = charset||diyBase.dftBase;
    hasZero = hasZero!==undefined?!!hasZero:false;
    var hz = (1^hasZero),cl = charset.length;
    var numList = c.split('').reduce(function (p, v, i,a) {
        var idx = charset.indexOf(v) + hz, pow = Math.pow(cl, a.length - 1 - i);
        p[i] = idx * pow;
        return p;
    },[0]);
    return numList.reduce(function (p, v) {
        p += v;
        return p;
    }, 0)-hz;
}

写完了感觉别人好, 一段代码就把所有的事情做完了. 后面还是想办法把BigInteger.js弄过来, 然后好好把玩
2023-05-16 续.

https://github.com/peterolson/BigInteger.js这个地址是有效的. 另外, base_symbols 的值也修正了.
原文: https://stackoverflow.com/questions/49541184/anyway-to-compress-a-string-to-something-smaller-in-javascript-and-make-it-reve

测试一下别人的代码:

var input = 'SigV1i8njyrAGrbAfHRNdM3fmEu3kd7keGsqTTDG3Wt3tXqT153eFya2JsEigrK7Pjmh6HhEQLp5bmNXyeHsKNELW7cD3';
var a = baseConvert(input, 62, 80);
var b = baseConvert(a, 80, 62);
console.log('%s\n%s\n%s\n', input, a, b);

完美.