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package org.openslx.imagemaster.crcchecker;
import java.io.IOException;
import java.util.zip.CRC32;
public class CrcChecker
{
private static final int blockSize = 16 * 1024 * 1024;
private ImageFile imageFile;
private CrcFile crcFile;
private byte[] block = new byte[ blockSize ]; // array that is used to read the blocks
/**
* Initialize a crc checker with an image file and a crc file.
*
* @param imageFile The image file to check
* @param crcFile The crc file to check against
*/
public CrcChecker( ImageFile imageFile, CrcFile crcFile )
{
this.imageFile = imageFile;
this.crcFile = crcFile;
}
public void done()
{
imageFile.close();
}
public boolean hasValidCrcFile()
{
return crcFile.isValid();
}
/**
* Checks a chosen block against the crc file.
*
* @param block The block to check
* @return Whether the block was valid or not
* @throws IOException When image or crc file could not be read.
*/
public boolean checkBlock( int blockNumber ) throws IOException
{
if ( !this.hasValidCrcFile() )
return false;
int length;
try {
length = imageFile.getBlock( blockNumber, block );
} catch ( IOException e ) {
throw new IOException( "image", e );
}
if ( length <= 0 )
return false;
CRC32 crcCalc = new CRC32();
if ( length == blockSize ) {
crcCalc.update( block );
} else {
crcCalc.update( block, 0, length );
}
int crcSum = Integer.reverseBytes( (int)crcCalc.getValue() );
int crcSumFromFile;
crcSumFromFile = crcFile.getCRCSum( blockNumber );
return ( crcSum == crcSumFromFile );
}
}
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