base64Decode.js

/**
	{
        "id": "com.perlovs.Esse.ExternalFunctions.base64Decode",
		"name":"Decode Base64",
		"description":"Decodes Base64",
		"category":"Developer",
		"author":"Perlovs",
	}
**/

function b64ToUint6 (nChr) {

  return nChr > 64 && nChr < 91 ?
      nChr - 65
    : nChr > 96 && nChr < 123 ?
      nChr - 71
    : nChr > 47 && nChr < 58 ?
      nChr + 4
    : nChr === 43 ?
      62
    : nChr === 47 ?
      63
    :
      0;

}

function base64DecToArr (sBase64, nBlocksSize) {

  var
    sB64Enc = sBase64.replace(/[^A-Za-z0-9\+\/]/g, ""), nInLen = sB64Enc.length,
    nOutLen = nBlocksSize ? Math.ceil((nInLen * 3 + 1 >> 2) / nBlocksSize) * nBlocksSize : nInLen * 3 + 1 >> 2, taBytes = new Uint8Array(nOutLen);

  for (var nMod3, nMod4, nUint24 = 0, nOutIdx = 0, nInIdx = 0; nInIdx < nInLen; nInIdx++) {
    nMod4 = nInIdx & 3;
    nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << 6 * (3 - nMod4);
    if (nMod4 === 3 || nInLen - nInIdx === 1) {
      for (nMod3 = 0; nMod3 < 3 && nOutIdx < nOutLen; nMod3++, nOutIdx++) {
        taBytes[nOutIdx] = nUint24 >>> (16 >>> nMod3 & 24) & 255;
      }
      nUint24 = 0;

    }
  }

  return taBytes;
}

function UTF8ArrToStr (aBytes) {

  var sView = "";

  for (var nPart, nLen = aBytes.length, nIdx = 0; nIdx < nLen; nIdx++) {
    nPart = aBytes[nIdx];
    sView += String.fromCharCode(
      nPart > 251 && nPart < 254 && nIdx + 5 < nLen ? /* six bytes */
        /* (nPart - 252 << 30) may be not so safe in ECMAScript! So...: */
        (nPart - 252) * 1073741824 + (aBytes[++nIdx] - 128 << 24) + (aBytes[++nIdx] - 128 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
      : nPart > 247 && nPart < 252 && nIdx + 4 < nLen ? /* five bytes */
        (nPart - 248 << 24) + (aBytes[++nIdx] - 128 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
      : nPart > 239 && nPart < 248 && nIdx + 3 < nLen ? /* four bytes */
        (nPart - 240 << 18) + (aBytes[++nIdx] - 128 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
      : nPart > 223 && nPart < 240 && nIdx + 2 < nLen ? /* three bytes */
        (nPart - 224 << 12) + (aBytes[++nIdx] - 128 << 6) + aBytes[++nIdx] - 128
      : nPart > 191 && nPart < 224 && nIdx + 1 < nLen ? /* two bytes */
        (nPart - 192 << 6) + aBytes[++nIdx] - 128
      : /* nPart < 127 ? */ /* one byte */
        nPart
    );
  }

  return sView;

}

function main(input) {
	if (input !== '') {
		return UTF8ArrToStr(base64DecToArr(input));
	}

	return input
}