signal-desktop/libtextsecure/stringview.js

/*
 * vim: ts=4:sw=4:expandtab
 */
;(function() {
    "use strict";

    window.StringView = {

      /*
      * These functions from the Mozilla Developer Network
      * and have been placed in the public domain.
      * https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding
      * https://developer.mozilla.org/en-US/docs/MDN/About#Copyrights_and_licenses
      */

      b64ToUint6: function(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;
      },

      base64ToBytes: function(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;
        var aBBytes = new ArrayBuffer(nOutLen);
        var taBytes = new Uint8Array(aBBytes);

        for (var nMod3, nMod4, nUint24 = 0, nOutIdx = 0, nInIdx = 0; nInIdx < nInLen; nInIdx++) {
          nMod4 = nInIdx & 3;
          nUint24 |= StringView.b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << 18 - 6 * 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 aBBytes;
      },

      uint6ToB64: function(nUint6) {
        return nUint6 < 26 ?
            nUint6 + 65
          : nUint6 < 52 ?
            nUint6 + 71
          : nUint6 < 62 ?
            nUint6 - 4
          : nUint6 === 62 ?
            43
          : nUint6 === 63 ?
            47
          :
            65;
      },

      bytesToBase64: function(aBytes) {
        var nMod3, sB64Enc = "";
        for (var nLen = aBytes.length, nUint24 = 0, nIdx = 0; nIdx < nLen; nIdx++) {
          nMod3 = nIdx % 3;
          if (nIdx > 0 && (nIdx * 4 / 3) % 76 === 0) { sB64Enc += "\r\n"; }
          nUint24 |= aBytes[nIdx] << (16 >>> nMod3 & 24);
          if (nMod3 === 2 || aBytes.length - nIdx === 1) {
            sB64Enc += String.fromCharCode(
                            StringView.uint6ToB64(nUint24 >>> 18 & 63),
                            StringView.uint6ToB64(nUint24 >>> 12 & 63),
                            StringView.uint6ToB64(nUint24 >>> 6 & 63),
                            StringView.uint6ToB64(nUint24 & 63)
                      );
            nUint24 = 0;
          }
        }
        return sB64Enc.replace(/A(?=A$|$)/g, "=");
      }
    };
}());