67 lines
2.8 KiB
C
67 lines
2.8 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 <avr/pgmspace.h>
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#include "Hamming.h"
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// This contains all of the precalculated parity values for a byte (8 bits).
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// This is very fast, but takes up more program space than calculating on the fly.
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static const byte _hammingCalculateParityFast128[256] PROGMEM =
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{
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0, 3, 5, 6, 6, 5, 3, 0, 7, 4, 2, 1, 1, 2, 4, 7,
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9, 10, 12, 15, 15, 12, 10, 9, 14, 13, 11, 8, 8, 11, 13, 14,
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10, 9, 15, 12, 12, 15, 9, 10, 13, 14, 8, 11, 11, 8, 14, 13,
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3, 0, 6, 5, 5, 6, 0, 3, 4, 7, 1, 2, 2, 1, 7, 4,
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11, 8, 14, 13, 13, 14, 8, 11, 12, 15, 9, 10, 10, 9, 15, 12,
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2, 1, 7, 4, 4, 7, 1, 2, 5, 6, 0, 3, 3, 0, 6, 5,
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1, 2, 4, 7, 7, 4, 2, 1, 6, 5, 3, 0, 0, 3, 5, 6,
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8, 11, 13, 14, 14, 13, 11, 8, 15, 12, 10, 9, 9, 10, 12, 15,
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12, 15, 9, 10, 10, 9, 15, 12, 11, 8, 14, 13, 13, 14, 8, 11,
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5, 6, 0, 3, 3, 0, 6, 5, 2, 1, 7, 4, 4, 7, 1, 2,
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6, 5, 3, 0, 0, 3, 5, 6, 1, 2, 4, 7, 7, 4, 2, 1,
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15, 12, 10, 9, 9, 10, 12, 15, 8, 11, 13, 14, 14, 13, 11, 8,
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7, 4, 2, 1, 1, 2, 4, 7, 0, 3, 5, 6, 6, 5, 3, 0,
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14, 13, 11, 8, 8, 11, 13, 14, 9, 10, 12, 15, 15, 12, 10, 9,
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13, 14, 8, 11, 11, 8, 14, 13, 10, 9, 15, 12, 12, 15, 9, 10,
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4, 7, 1, 2, 2, 1, 7, 4, 3, 0, 6, 5, 5, 6, 0, 3,
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};
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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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return pgm_read_byte(&(_hammingCalculateParityFast128[value]));
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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 (pgm_read_byte(&(_hammingCalculateParityFast128[second]))<<4) | pgm_read_byte(&(_hammingCalculateParityFast128[first]));
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}
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