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Declarative Machine Learning
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.sysml.runtime.compress;
import java.util.Iterator;
/**
* General-purpose iterator to decode a compressed OLE bitmap.
*
*/
public final class BitmapDecoderRLE implements Iterator
{
// pointer to the compressed bitmap
private int _bmOff;
private int _bmLen;
private char[] _bmPtr;
// The offset of the next element we will read from the bitmap, or
// bmPtr.length if we are done.
private int _nextBmOffset;
// The offset in the matrix column of the beginning of the current run
private int _runStartOffset;
// The length of the current run
private int _curRunLen;
// The number of bits that we have returned from the current run.
private int _runBitsReturned;
/**
* Point this object at the beginning of a particular bitmap. After a call
* to this method, the next call to {@link #next()} will return the
* offset of the first bit in the specified bitmap.
*
* @param bmPtr
* pointer to a compressed bitmap
* @param off offset
* @param len length
*/
public BitmapDecoderRLE(char[] bmPtr, int off, int len) {
_bmOff = off;
_bmLen = len;
_bmPtr = bmPtr;
_nextBmOffset = 0;
_runStartOffset = 0;
_curRunLen = 0;
_runBitsReturned = 0;
if (0 == _bmLen) {
return; //no runs
}
// Advance to the beginning of the first non-empty run.
advanceToNextRun();
}
@Override
public Integer next() {
if( !hasNext() )
throw new RuntimeException("No next offset existing.");
// Grab the lookahead value
int ret = _runStartOffset + _runBitsReturned;
_runBitsReturned++;
// Check for end of run
if (_runBitsReturned == _curRunLen) {
advanceToNextRun();
}
return ret;
}
@Override
public boolean hasNext() {
return _runBitsReturned < _curRunLen;
}
@Override
public void remove() {
throw new RuntimeException("Not implemented for BitmapDecoderRLE.");
}
/** Move forward to the next non-empty run. */
private void advanceToNextRun() {
// While loop needed because some runs are of length 0
while (_runBitsReturned == _curRunLen && _nextBmOffset < _bmLen) {
_runBitsReturned = 0;
// Read the distance to the next run
char delta = _bmPtr[_bmOff + _nextBmOffset];
// Run length is stored in the next element of the array
_runStartOffset += delta + _curRunLen;
_curRunLen = _bmPtr[_bmOff + _nextBmOffset + 1];
_nextBmOffset += 2;
}
}
}