package it.unimi.dsi.bits;
/*
* DSI utilities
*
* Copyright (C) 2007-2009 Sebastiano Vigna
*
* 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 program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
*/
import it.unimi.dsi.compression.PrefixCodec;
import it.unimi.dsi.compression.PrefixCoder;
import it.unimi.dsi.fastutil.chars.Char2IntMap;
import it.unimi.dsi.fastutil.chars.Char2IntOpenHashMap;
/** A transformation strategy mapping strings using a {@linkplain PrefixCodec prefix-free encoder}.
*
* <p>The actual encoding must be provided via a map from characters to symbols, and a set
* of codewords. The default return value of the map will be used for unknown characters.
*
* <p>This strategy creates a new {@link LongArrayBitVector} each time {@link #toBitVector(CharSequence)} is invoked.
*/
public class PrefixCoderTransformationStrategy implements TransformationStrategy<CharSequence> {
private static final long serialVersionUID = 1;
protected final BitVector[] codeWord;
protected final Char2IntOpenHashMap char2symbol;
protected final boolean prefixFree;
/** Create a new transformation strategy based on a prefix-free coder.
*
* @param coder a prefix-free coder.
* @param char2symbol a map from character to symbols (the default returned value will be used for unknown symbols).
* @param prefixFree whether it is required that the resulting bit vectors are prefix-free: in this case, symbol 0 will
* be appended to each string, and will not be allowed to appear in any string.
*/
public PrefixCoderTransformationStrategy( final PrefixCoder coder, final Char2IntOpenHashMap char2symbol, final boolean prefixFree ) {
this( coder.codeWords(), char2symbol, prefixFree );
}
protected PrefixCoderTransformationStrategy( final PrefixCoderTransformationStrategy transformationStrategy ) {
this( transformationStrategy.codeWord, transformationStrategy.char2symbol, transformationStrategy.prefixFree );
}
protected PrefixCoderTransformationStrategy( final BitVector[] codeWord, final Char2IntOpenHashMap char2symbol, final boolean prefixFree ) {
this.codeWord = codeWord;
this.char2symbol = char2symbol;
this.prefixFree = prefixFree;
}
public LongArrayBitVector toBitVector( final CharSequence s ) {
final BitVector[] codeWord = this.codeWord;
final Char2IntMap char2symbol = this.char2symbol;
final int length = s.length();
int numBits = prefixFree ? codeWord[ 0 ].size() : 0;
for( int i = length; i-- != 0; ) numBits += codeWord[ char2symbol.get( s.charAt( i ) ) ].size();
final LongArrayBitVector result = LongArrayBitVector.getInstance( numBits );
for( int i = 0; i < s.length(); i++ ) result.append( codeWord[ char2symbol.get( s.charAt( i ) ) ] );
if ( prefixFree ) result.append( codeWord[ 0 ] );
return result;
}
public long numBits() {
long numBits = 0;
for( int i = codeWord.length; i-- != 0; ) numBits += codeWord[ i ].size();
return numBits;
}
public PrefixCoderTransformationStrategy copy() {
return new PrefixCoderTransformationStrategy( this );
}
}