/*
* JBoss, Home of Professional Open Source.
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership. Some portions may be licensed
* to Red Hat, Inc. under one or more contributor license agreements.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301 USA.
*/
package org.teiid.core.types;
import java.io.IOException;
import java.io.InputStream;
import java.sql.SQLException;
import org.teiid.runtime.client.Messages;
public class LobSearchUtil {
private static final int MOD = 37;
public interface StreamProvider {
InputStream getBinaryStream() throws SQLException;
}
static long position(StreamProvider pattern, long patternLength, StreamProvider target, long targetLength, long start, int bytesPerComparison) throws SQLException {
if (pattern == null) {
return -1;
}
patternLength *= bytesPerComparison;
targetLength *= bytesPerComparison;
if (start < 1) {
Object[] params = new Object[] {new Long(start)};
throw new SQLException(Messages.getString(Messages.MMClob.MMBlob_2, params));
}
start = (start - 1)*bytesPerComparison;
if (start + patternLength > targetLength) {
return -1;
}
/*
* Use karp-rabin matching to reduce the cost of back tracing for failed matches
*
* TODO: optimize for patterns that are small enough to fit in a reasonable buffer
*/
try {
InputStream patternStream = pattern.getBinaryStream();
InputStream targetStream = target.getBinaryStream();
InputStream laggingTargetStream = target.getBinaryStream();
try {
int patternHash = computeStreamHash(patternStream, patternLength);
int lastMod = 1;
for (int i = 0; i < patternLength; i++) {
lastMod *= MOD;
}
targetStream.skip(start);
laggingTargetStream.skip(start);
long position = start + 1;
int streamHash = computeStreamHash(targetStream, patternLength);
do {
if ((position -1)%bytesPerComparison == 0 && patternHash == streamHash && validateMatch(pattern, target, position)) {
return (position - 1)/bytesPerComparison + 1;
}
streamHash = MOD * streamHash + targetStream.read() - lastMod * laggingTargetStream.read();
position++;
} while (position + patternLength - 1 <= targetLength);
return -1;
} finally {
if (patternStream != null) {
patternStream.close();
}
if (targetStream != null) {
targetStream.close();
}
if (laggingTargetStream != null) {
laggingTargetStream.close();
}
}
} catch (IOException e) {
throw new SQLException(e);
}
}
/**
* validate that the pattern matches the given position.
*
* TODO: optimize to reuse the same targetstream/buffer for small patterns
* @throws SQLException
*/
static private boolean validateMatch(StreamProvider pattern, StreamProvider target, long position) throws IOException, SQLException {
InputStream targetStream = target.getBinaryStream();
InputStream patternStream = pattern.getBinaryStream();
try {
targetStream.skip(position -1);
int value = 0;
while ((value = patternStream.read()) != -1) {
if (value != targetStream.read()) {
return false;
}
}
} finally {
targetStream.close();
patternStream.close();
}
return true;
}
static private int computeStreamHash(InputStream is, long length) throws IOException {
int result = 0;
for (int i = 0; i < length; i++) {
result = result * MOD + is.read();
}
return result;
}
}