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package org.openslx.imagemaster.crcchecker;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.CRC32;
/**
* Represents a crcfile
* @author nils
*
*/
public class CRCFile
{
private File file;
private List<Integer> crcSums = null;
CRCFile(String filename) {
this.file = new File( filename );
}
/**
* Checks if this crc file is valid.
* (If the crc over the file is equal to the first crc sum.)
* @return Whether the crc file is valid
* @throws IOException If the file could not be read or could not be found
*/
public boolean isValid() throws IOException {
FileInputStream fis = new FileInputStream( file );
DataInputStream dis = new DataInputStream( fis );
int crcSum = dis.readInt();
CRC32 crcCalc = new CRC32();
byte[] bytes = new byte[(int) file.length() - Integer.SIZE/8]; // byte array with length of the file minus the first crc sum (=4byte)
fis.read( bytes );
crcCalc.update( bytes );
dis.close();
if (crcSum == Integer.reverseBytes( (int) crcCalc.getValue() ) ) return true;
else return false;
}
/**
* Get a specified crcSum for a block number
* @param blockNumber
* @return The crcSum or 0 if the block number is invalid
* @throws IOException
*/
public int getCRCSum(int blockNumber) throws IOException {
if (crcSums == null) {
// the crcSums were not read yet
DataInputStream dis = new DataInputStream( new FileInputStream( file ) );
crcSums = new ArrayList<>();
for (int i = 0; i < file.length()/4; i++) {
int s = dis.readInt();
if (i > 0) crcSums.add( s ); // skip the first crcSum because it's the sum over the crcFile
}
dis.close();
}
if (blockNumber < 0) return 0;
if (blockNumber > crcSums.size() - 1) return 0;
return crcSums.get( blockNumber );
}
}
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