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Adds Galois 24/12/7 error correction and detection for use with P25 decoder.

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dennis.sheirer
2014-12-26 19:51:25 +00:00
parent c28cf19104
commit f6687decef
6 changed files with 329 additions and 30 deletions
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65
src/crc/CRCUtil.java
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@@ -50,12 +50,10 @@ public class CRCUtil
message.set( x );
message = decode( message, messageSize, polynomial, crcSize );
message = decode( message, 0, messageSize, polynomial, crcSize );
long checksum = message.getLong( checksumIndexes );
mLog.debug( "Index " + x + " Checksum:" + Long.toHexString( checksum ) );
crcTable[ x ] = checksum;
}
@@ -70,6 +68,48 @@ public class CRCUtil
return crcTable;
}
/**
* Generates the checksum table and treats the final bit of each check value
* as a parity bit that complies with the request parity argument.
*/
public static long[] generate( int messageSize,
int crcSize,
long polynomial,
long initialFill,
boolean includeCRCBitErrors,
Parity parity )
{
long[] table = generate( messageSize, crcSize, polynomial, initialFill,
includeCRCBitErrors );
if( parity == Parity.NONE )
{
return table;
}
else
{
for( int x = 0; x < table.length; x++ )
{
table[ x ] <<= 1;
if( parity( table[ x ] ) != parity )
{
table[ x ] ^= 0x1;
}
}
return table;
}
}
public enum Parity{ EVEN, ODD, NONE };
/* Determines the parity (number of 1 bits) for the value */
public static Parity parity( long value )
{
return Long.bitCount( value ) % 2 == 0 ? Parity.EVEN : Parity.ODD;
}
/**
* Performs binary division of the polynomial into the message for bits
@@ -91,14 +131,13 @@ public class CRCUtil
* placed in the crc field which starts at index messageLength
*/
public static BitSetBuffer decode( BitSetBuffer message,
int messageStart,
int messageSize,
long polynomial,
int crcSize )
{
int MESSAGE_START = 0;
for (int i = message.nextSetBit( MESSAGE_START );
i >= MESSAGE_START && i < messageSize;
for (int i = message.nextSetBit( messageStart );
i >= messageStart && i < messageSize;
i = message.nextSetBit( i+1 ) )
{
BitSetBuffer polySet = new BitSetBuffer( crcSize + i + 1 );
@@ -115,17 +154,9 @@ public class CRCUtil
{
mLog.debug( "Starting" );
long polynomial = 0x104C11DB7l;
long polynomial = 0xC75l;
// String raw = "101111101110000000000000001101111110001100111100001110000111000011111111101010111011000011100100";
// BitSetBuffer buffer = BitSetBuffer.load( raw );
// mLog.debug( "ORIG:" + buffer.toString() );
// BitSetBuffer processed = decode( buffer, 64, polynomial, 32 );
// mLog.debug( "PROC:" + processed.toString() );
long[] table = generate( 256, 32, 0x104C11DB7l, 0xFFFFFFFFl, true );
// long[] table = generate( 80, 16, 0x11021l, 0xFFFFl, true );
long[] table = generate( 12, 11, polynomial, 0x0, true, Parity.NONE );
mLog.debug( toCodeArray( table ) );
mLog.debug( "Finished" );
}