64转2

/*
	Copyright (c) 2011, Daniel Guerrero
	All rights reserved.
	Redistribution and use in source and binary forms, with or without
	modification, are permitted provided that the following conditions are met:
	* Redistributions of source code must retain the above copyright
	notice, this list of conditions and the following disclaimer.
	* Redistributions in binary form must reproduce the above copyright
	notice, this list of conditions and the following disclaimer in the
	documentation and/or other materials provided with the distribution.
	THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
	ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
	WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	DISCLAIMED. IN NO EVENT SHALL DANIEL GUERRERO BE LIABLE FOR ANY
	DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
	(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
	ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
	SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/
	/**
	* Uses the new array typed in javascript to binary base64 encode/decode
	* at the moment just decodes a binary base64 encoded
	* into either an ArrayBuffer (decodeArrayBuffer)
	* or into an Uint8Array (decode)
	*
	* References:
	* https://developer.mozilla.org/en/JavaScript_typed_arrays/ArrayBuffer
	* https://developer.mozilla.org/en/JavaScript_typed_arrays/Uint8Array
	*/
	var Base64Binary = {
	_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
	/* will return a Uint8Array type */
	decodeArrayBuffer: function(input) {
	var bytes = (input.length/4) * 3;
	var ab = new ArrayBuffer(bytes);
	this.decode(input, ab);
	return ab;
	},
	removePaddingChars: function(input){
	var lkey = this._keyStr.indexOf(input.charAt(input.length - 1));
	if(lkey == 64){
	return input.substring(0,input.length - 1);
	}
	return input;
	},
	decode: function (input, arrayBuffer) {
	//get last chars to see if are valid
	input = this.removePaddingChars(input);
	input = this.removePaddingChars(input);
	var bytes = parseInt((input.length / 4) * 3, 10);
	var uarray;
	var chr1, chr2, chr3;
	var enc1, enc2, enc3, enc4;
	var i = 0;
	var j = 0;
	if (arrayBuffer)
	uarray = new Uint8Array(arrayBuffer);
	else
	uarray = new Uint8Array(bytes);
	input = input.replace(/[^A-Za-z0-9+/=]/g, "");
	for (i=0; i<bytes; i+=3) {
	//get the 3 octects in 4 ascii chars
	enc1 = this._keyStr.indexOf(input.charAt(j++));
	enc2 = this._keyStr.indexOf(input.charAt(j++));
	enc3 = this._keyStr.indexOf(input.charAt(j++));
	enc4 = this._keyStr.indexOf(input.charAt(j++));
	chr1 = (enc1 << 2) | (enc2 >> 4);
	chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
	chr3 = ((enc3 & 3) << 6) | enc4;
	uarray[i] = chr1;
	if (enc3 != 64) uarray[i+1] = chr2;
	if (enc4 != 64) uarray[i+2] = chr3;
	}
	return uarray;
	}
	}