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+/*
+Hamming Error-Correcting Code (ECC)
+Optimized for avr-gcc 4.8.1 in Atmel AVR Studio 6.2
+August 12, 2014
+
+You should include Hamming.c, Hamming.h, and only one of the other Hamming files in your project.
+The other Hamming files implement the same methods in different ways, that may be better or worse for your needs.
+
+This was created for LoFi in the TheHackadayPrize contest.
+http://hackaday.io/project/1552-LoFi
+
+Copyright 2014 David Cook
+RobotRoom.com
+
+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.
+*/
+
+#include "Hamming.h"
+
+/****************************/
+/*                          */
+/*      Public  methods     */
+/*                          */
+/****************************/
+
+// This is slower than using a table, but faster than
+// using the textbook method.
+
+// Given a byte to transmit, this returns the parity as a nibble
+nibble HammingCalculateParity128(byte value)
+{
+	// Exclusive OR is associative and commutative, so order of operations and values does not matter.
+	nibble parity;
+
+	if ( ( value & 1 ) != 0 )
+	{
+		parity = 0x3;
+	}
+	else
+	{
+		parity = 0x0;
+	}
+
+	if ( ( value & 2 ) != 0 )
+	{
+		parity ^= 0x5;
+	}
+
+	if ( ( value & 4 ) != 0 )
+	{
+		parity ^= 0x6;
+	}
+
+	if ( ( value & 8 ) != 0 )
+	{
+		parity ^= 0x7;
+	}
+
+	if ( ( value & 16 ) != 0 )
+	{
+		parity ^= 0x9;
+	}
+
+	if ( ( value & 32 ) != 0 )
+	{
+		parity ^= 0xA;
+	}
+
+	if ( ( value & 64 ) != 0 )
+	{
+		parity ^= 0xB;
+	}
+
+	if ( ( value & 128 ) != 0 )
+	{
+		parity ^= 0xC;
+	}
+
+	return parity;
+}
+
+// Given two bytes to transmit, this returns the parity
+// as a byte with the lower nibble being for the first byte,
+// and the upper nibble being for the second byte.
+byte HammingCalculateParity2416(byte first, byte second)
+{
+	return (HammingCalculateParity128(second) << 4) | HammingCalculateParity128(first);
+}
+