Nodejs String to Ascii85 Convert toAscii85()

Method Source Code

String.prototype.toAscii85 = function() {
    let pad = '\0', addnum = 0, str = this, res = '', sum = 0;
    while (str.length % 4 !== 0)
    {/*from   w w w .ja  v  a2 s. c o  m*/
        str += pad;
        addnum ++;
    }
    for (let i = 0; i < str.length; i += 4)
    {
        let e = '';
        let temp = str.substr(i, 4);
        for (let j = 0; j < 4; j++)
        {
            let t = temp[j].charCodeAt().toString(2)
            while (t.length !== 8)
                t = '0' + t;
            e += t;
        }
        sum = parseInt(e, 2);
        let encode = [];
        for (let j = 0; j < 5; j++)
            encode.push(0);
        for (let j = 4; j >= 0; j--)
        {
            encode[j] = sum % 85;
            sum = Math.floor(sum / 85);
        }
        for (let j = 0; j < 5; j++)
            res += String.fromCharCode(encode[j] + 33);
    }
    res = res.substr(0, res.length - addnum);
    let newres = '', i = 0;
    for (i = 0; i < res.length; i += 5)
        newres += res.substr(i, Math.min(5, res.length - i)) === '!!!!!' ? 'z' : res.substr(i, Math.min(5, res.length - i));
    return '<~' + newres + '~>';
};

Related

1. toAscii85()

   String.prototype.toAscii85 = function() {
     var str = this, result = ''
     while (str.length) {
       let num = 0, j = 5, i = 4
       if (str.substr(0,4) == '\u0000\u0000\u0000\u0000') result += 'z'
       else {
         while (i--) {
           num += (str.charCodeAt(3-i) || 0)*Math.pow(2, 8*i)
         while (j-- && str.length > 3-j) {
           result += String.fromCharCode(num/Math.pow(85, j) % 85 + 33)
       str = str.substr(4)
     return `<~${result}~>`
   

2. toAscii85()

   String.prototype.toAscii85 = function() {
     var ret = "";
     for(var i=0; i<this.length; i+=4){
       var deficit = Math.max(0, 4+i-this.length);
       var nnn = 0;
       for(var j=0; j<4; j++){
         nnn = nnn*256 + (this.charCodeAt(i+j) || 0);
       var codes = [];
   ...
   

3. toAscii85()

   String.prototype.toAscii85 = function() {
     var str = '';
     for(var i = 0, len = this.length; i < len; i+=4) {
       var bin = '';
       var zeroes = 0;
       for(var j = 0; j < 4; j++) {
         var char = this[i+j];
         bin += to8bit(char ? char.charCodeAt(0) : (zeroes++, 0));
       var n = parseInt(bin, 2);
       for(var j = 4; j >= 0; j--) {
         var c = Math.floor(n / Math.pow(85, j));
         n -= c*Math.pow(85, j);
         str += String.fromCharCode(c + 33);
       str = str.slice(0, zeroes > 0 ? -zeroes : undefined);
     return '<~' + str.replace(/!{5}/g, 'z') + '~>'