99 lines
2.2 KiB
C
99 lines
2.2 KiB
C
/*
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Hamming Error-Correcting Code (ECC)
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Optimized for avr-gcc 4.8.1 in Atmel AVR Studio 6.2
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August 12, 2014
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You should include Hamming.c, Hamming.h, and only one of the other Hamming files in your project.
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The other Hamming files implement the same methods in different ways, that may be better or worse for your needs.
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This was created for LoFi in the TheHackadayPrize contest.
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http://hackaday.io/project/1552-LoFi
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Copyright 2014 David Cook
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RobotRoom.com
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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#include "Hamming.h"
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/****************************/
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/* */
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/* Public methods */
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/* */
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/****************************/
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// This is slower than using a table, but faster than
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// using the textbook method.
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// Given a byte to transmit, this returns the parity as a nibble
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nibble HammingCalculateParity128(byte value)
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{
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// Exclusive OR is associative and commutative, so order of operations and values does not matter.
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nibble parity;
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if ( ( value & 1 ) != 0 )
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{
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parity = 0x3;
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}
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else
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{
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parity = 0x0;
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}
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if ( ( value & 2 ) != 0 )
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{
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parity ^= 0x5;
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}
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if ( ( value & 4 ) != 0 )
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{
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parity ^= 0x6;
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}
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if ( ( value & 8 ) != 0 )
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{
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parity ^= 0x7;
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}
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if ( ( value & 16 ) != 0 )
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{
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parity ^= 0x9;
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}
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if ( ( value & 32 ) != 0 )
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{
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parity ^= 0xA;
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}
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if ( ( value & 64 ) != 0 )
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{
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parity ^= 0xB;
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}
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if ( ( value & 128 ) != 0 )
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{
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parity ^= 0xC;
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}
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return parity;
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}
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// Given two bytes to transmit, this returns the parity
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// as a byte with the lower nibble being for the first byte,
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// and the upper nibble being for the second byte.
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byte HammingCalculateParity2416(byte first, byte second)
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{
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return (HammingCalculateParity128(second) << 4) | HammingCalculateParity128(first);
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}
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