BitStream

bitstream.js

/*
 * Copyright (c) 2011 Ivo Wetzel.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
var BitStream = (function() {

	var chrTable = new Array(255);
	for(var i = 0; i < 256; i++) {
		chrTable[i] = String.fromCharCode(i);
	}

	var maskTable = new Array(8),
		powTable = new Array(8);

	for(var i = 0; i < 9; i++) {
		maskTable[i] = ~((powTable[i] = Math.pow(2, i) - 1) ^ 0xFF);
	}

	var stream = '',
		value = 0,
		left = 8;

	return {

		open: function(data) {

			left = 8;
			if (data !== undefined) {
				index = 0;
				stream = data;
				value = stream.charCodeAt(index);

			} else {
				value = 0;
				stream = '';

			}

		},

		end: function() {

			if (value > 0) {
				stream += chrTable[value];
			}

			return stream;

		},

		write: function write(val, count) {

			var overflow = count - left,
				use = left < count ? left : count,
				shift = left - use;

			if (overflow > 0) {
				value += val >> overflow << shift;

			} else {
				value += val << shift;
			}

			left -= use;

			if (left === 0) {

				stream += chrTable[value];
				left = 8;
				value = 0;

				if (overflow > 0) {
					write(val & powTable[overflow], overflow);
				}

			}

		},

		read: function read(count) {

			var overflow = count - left,
				use = left < count ? left : count,
				shift = left - use;

			var val = (value & maskTable[left]) >> shift;

			left -= use;

			if (left === 0) {

				value = stream.charCodeAt(++index);
				left = 8;

				if (overflow > 0) {
					console.log('Wrap')
					val = val << overflow | read(overflow);
				}

			}

			console.log(val)
			return val;

		}

	};

})();


function bin(value, len) {
	var bin = value.toString(2);
	return new Array((len + 1) - bin.length).join('0') + bin;
}

BitStream.open();
BitStream.write(1, 2)
BitStream.write(2, 4)
BitStream.write(15, 4)
BitStream.write(15, 4)
BitStream.write(3, 2)
BitStream.write(1, 1)

var data = BitStream.end();
BitStream.open(data);
BitStream.read(2);
BitStream.read(4);
BitStream.read(4);
BitStream.read(4);
BitStream.read(2);
BitStream.read(1);