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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.Arrays;
import java.util.Iterator;
/**
* General-purpose iterator to decode a compressed OLE bitmap.
*
*/
public final class BitmapDecoderOLE implements Iterator
{
// pointer to the compressed bitmap
private int _bmOff;
private int _bmLen;
private char[] _bmPtr;
// The index of the current block. Block 0 covers bits 1 through 2^16
private int _blockIx;
// The offset where the current block starts within the bitmap.
private int _blockStartOffset;
// The number of offsets in the current block.
private int _curBlockSize;
// The offset in the current block the next element we will
// read from the bitmap, or bmPtr.length if we are done.
private int _nextBmOffset;
/**
* Point this object at the beginning of a particular bitmap. After a call
* to this method, the next call to {@link #nextOffset()} will return the
* offset of the first bit in the specified bitmap.
*
* @param bmPtr
* pointer to a compressed bitmap
*/
public BitmapDecoderOLE(char[] bmPtr, int off, int len) {
_bmOff = off;
_bmLen = len;
_bmPtr = bmPtr;
_blockIx = 0;
_blockStartOffset = 0;
_curBlockSize = _bmPtr[_bmOff+_blockStartOffset];
if (_curBlockSize < 0) {
throw new RuntimeException(String.format(
"Negative block size %d at position %d of %s",
_curBlockSize, _blockStartOffset, Arrays.toString(bmPtr)));
}
_nextBmOffset = 0;
// Advance past any zero-length blocks at the beginning of the array
while (_blockStartOffset < _bmLen
&& _nextBmOffset >= _curBlockSize) {
advanceToNextBlock();
}
}
@Override
public Integer next() {
if( !hasNext() )
throw new RuntimeException("No next offset existing.");
// Grab the lookahead value Note the +1 in the array indexing;
// the first number in a block is the block size
int offsetFromBlockBegin = _bmPtr[_bmOff+_blockStartOffset + 1 + _nextBmOffset];
int ret = (_blockIx * BitmapEncoder.BITMAP_BLOCK_SZ)
+ offsetFromBlockBegin;
_nextBmOffset++;
// Advance to next non-empty block if we reached the end of the block.
while (_blockStartOffset < _bmLen && _nextBmOffset >= _curBlockSize) {
advanceToNextBlock();
}
return ret;
}
@Override
public boolean hasNext() {
return _blockStartOffset < _bmLen;
}
@Override
public void remove() {
throw new RuntimeException("Not implemented for BitmapDecoderOLE.");
}
/**
* Move forward to the next block. Does not skip empty blocks.
*/
private void advanceToNextBlock() {
_blockStartOffset += (1 + _curBlockSize);
_blockIx++;
if (_blockStartOffset >= _bmLen) {
// Read past last block
return;
}
_curBlockSize = _bmPtr[_bmOff+_blockStartOffset];
if (_curBlockSize < 0) {
throw new RuntimeException(String.format(
"Negative block size %d at position %d of %s",
_curBlockSize, _blockStartOffset, Arrays.toString(_bmPtr)));
}
_nextBmOffset = 0;
}
}