gf256.js

/*
  Ported to JavaScript by Lazar Laszlo 2011 
  
  lazarsoft@gmail.com, www.lazarsoft.info
  
*/

/*
*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/


function GF256( primitive)
{
	this.expTable = new Array(256);
	this.logTable = new Array(256);
	var x = 1;
	for (var i = 0; i < 256; i++)
	{
		this.expTable[i] = x;
		x <<= 1; // x = x * 2; we're assuming the generator alpha is 2
		if (x >= 0x100)
		{
			x ^= primitive;
		}
	}
	for (var i = 0; i < 255; i++)
	{
		this.logTable[this.expTable[i]] = i;
	}
	// logTable[0] == 0 but this should never be used
	var at0=new Array(1);at0[0]=0;
	this.zero = new GF256Poly(this, new Array(at0));
	var at1=new Array(1);at1[0]=1;
	this.one = new GF256Poly(this, new Array(at1));
	
	this.__defineGetter__("Zero", function()
	{
		return this.zero;
	});
	this.__defineGetter__("One", function()
	{
		return this.one;
	});
	this.buildMonomial=function( degree,  coefficient)
		{
			if (degree < 0)
			{
				throw "System.ArgumentException";
			}
			if (coefficient == 0)
			{
				return zero;
			}
			var coefficients = new Array(degree + 1);
			for(var i=0;i<coefficients.length;i++)coefficients[i]=0;
			coefficients[0] = coefficient;
			return new GF256Poly(this, coefficients);
		}
	this.exp=function( a)
		{
			return this.expTable[a];
		}
	this.log=function( a)
		{
			if (a == 0)
			{
				throw "System.ArgumentException";
			}
			return this.logTable[a];
		}
	this.inverse=function( a)
		{
			if (a == 0)
			{
				throw "System.ArithmeticException";
			}
			return this.expTable[255 - this.logTable[a]];
		}
	this.multiply=function( a,  b)
		{
			if (a == 0 || b == 0)
			{
				return 0;
			}
			if (a == 1)
			{
				return b;
			}
			if (b == 1)
			{
				return a;
			}
			return this.expTable[(this.logTable[a] + this.logTable[b]) % 255];
		}		
}

GF256.QR_CODE_FIELD = new GF256(0x011D);
GF256.DATA_MATRIX_FIELD = new GF256(0x012D);

GF256.addOrSubtract=function( a,  b)
{
	return a ^ b;
}