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/*
Copyright (c) 2005 Health Market Science, Inc.
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307
USA
You can contact Health Market Science at info@healthmarketscience.com
or at the following address:
Health Market Science
2700 Horizon Drive
Suite 200
King of Prussia, PA 19406
*/
package com.healthmarketscience.jackcess.impl;
import java.nio.ByteBuffer;
/**
* Bitmask that indicates whether or not each column in a row is null. Also
* holds values of boolean columns.
* @author Tim McCune
*/
public class NullMask {
/** num row columns */
private final int _columnCount;
/** The actual bitmask */
private final byte[] _mask;
/**
* @param columnCount Number of columns in the row that this mask will be
* used for
*/
public NullMask(int columnCount) {
_columnCount = columnCount;
// we leave everything initially marked as null so that we don't need to
// do anything for deleted columns (we only need to mark as non-null
// valid columns for which we actually have values).
_mask = new byte[(_columnCount + 7) / 8];
}
/**
* Read a mask in from a buffer
*/
public void read(ByteBuffer buffer) {
buffer.get(_mask);
}
/**
* Write a mask to a buffer
*/
public void write(ByteBuffer buffer) {
buffer.put(_mask);
}
/**
* @param column column to test for {@code null}
* @return Whether or not the value for that column is null. For boolean
* columns, returns the actual value of the column (where
* non-{@code null} == {@code true})
*/
public boolean isNull(ColumnImpl column) {
int columnNumber = column.getColumnNumber();
// if new columns were added to the table, old null masks may not include
// them (meaning the field is null)
if(columnNumber >= _columnCount) {
// it's null
return true;
}
return (_mask[byteIndex(columnNumber)] & bitMask(columnNumber)) == 0;
}
/**
* Indicate that the column with the given number is not {@code null} (or a
* boolean value is {@code true}).
* @param column column to be marked non-{@code null}
*/
public void markNotNull(ColumnImpl column) {
int columnNumber = column.getColumnNumber();
int maskIndex = byteIndex(columnNumber);
_mask[maskIndex] = (byte) (_mask[maskIndex] | bitMask(columnNumber));
}
/**
* @return Size in bytes of this mask
*/
public int byteSize() {
return _mask.length;
}
private static int byteIndex(int columnNumber) {
return columnNumber / 8;
}
private static byte bitMask(int columnNumber) {
return (byte) (1 << (columnNumber % 8));
}
}
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