Base64 to DataView

base64_decode_dataview.js

var base64_decode_dataview = (function() {
	var   __map = {}
		, __map_18 = {}
		, __map_12 = {}
		, __map_6 = {};

	!function() {
		var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

		 for (var i = 0, j = chars.length, c; i < j; i ++) {
		 	c = chars.charAt(i);
		 	__map[c] = i;
		 	__map_18[c] = i << 18;
		 	__map_12[c] = i << 12;
		 	__map_6[c] = i << 6;
		 }
	}();

	return function(_a, callback) {
		if (_a.indexOf('\n') !== -1)
			_a = _a.replace(/\n/g, '');

		var execute = function() {
			var   a = _a
				, map_18 = __map_18
				, map_12 = __map_12
				, map_6 = __map_6
				, map = __map
				, length = a.length
				, padindex = a.indexOf('=')
				, padlen = padindex > -1 ? length - padindex : 0
				, result = new DataView(new ArrayBuffer(length * 3 / 4 - padlen))
				, offset = 0
				, last = length - 4 - (length % 4);

			for (var i = 0, padding_length, len, n; i < length; i += 4) {
				if (i === last) {
					len = 4 - (padlen || (i + 4) - length);
					padding_length = len % 4;

					n = (len > 0 ? map_18[a[i + 0]] : 0) |
						(len > 1 ? map_12[a[i + 1]] : 0) |
						(len > 2 ? map_6[a[i + 2]] : 0) |
						(len > 3 ? map[a[i + 3]] : 0);
				} else {
					padding_length = 0;
					n = map_18[a[i + 0]] | map_12[a[i + 1]] | map_6[a[i + 2]] | map[a[i + 3]];
				}

				switch (padding_length) {
				case 0:
				case 1:
					result.setUint8(offset ++, n >>> 16);
					result.setUint8(offset ++, (n >>> 8) & 0xff);
					result.setUint8(offset ++, n & 0xff);
					break;
				case 2:
					result.setUint8(offset ++, n >>> 16);
					break;
				case 3:
					result.setUint8(offset ++, n >>> 16);
					result.setUint8(offset ++, (n >>> 8) & 0xff);
					break;
				}
			}

			return result;
		};

		if (callback) {
			setTimeout(function() {
				callback(execute());
			}, 0);
		} else {
			return execute();
		}
	};
})();