/**
* 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.lucene.util;
import org.apache.lucene.search.DocIdSetIterator;
/** An iterator to iterate over set bits in an OpenBitSet.
* This is faster than nextSetBit() for iterating over the complete set of bits,
* especially when the density of the bits set is high.
*
* @version $Id$
*/
public class OpenBitSetIterator extends DocIdSetIterator {
// The General Idea: instead of having an array per byte that has
// the offsets of the next set bit, that array could be
// packed inside a 32 bit integer (8 4 bit numbers). That
// should be faster than accessing an array for each index, and
// the total array size is kept smaller (256*sizeof(int))=1K
protected final static int[] bitlist={
0x0, 0x1, 0x2, 0x21, 0x3, 0x31, 0x32, 0x321, 0x4, 0x41, 0x42, 0x421, 0x43,
0x431, 0x432, 0x4321, 0x5, 0x51, 0x52, 0x521, 0x53, 0x531, 0x532, 0x5321,
0x54, 0x541, 0x542, 0x5421, 0x543, 0x5431, 0x5432, 0x54321, 0x6, 0x61, 0x62,
0x621, 0x63, 0x631, 0x632, 0x6321, 0x64, 0x641, 0x642, 0x6421, 0x643,
0x6431, 0x6432, 0x64321, 0x65, 0x651, 0x652, 0x6521, 0x653, 0x6531, 0x6532,
0x65321, 0x654, 0x6541, 0x6542, 0x65421, 0x6543, 0x65431, 0x65432, 0x654321,
0x7, 0x71, 0x72, 0x721, 0x73, 0x731, 0x732, 0x7321, 0x74, 0x741, 0x742,
0x7421, 0x743, 0x7431, 0x7432, 0x74321, 0x75, 0x751, 0x752, 0x7521, 0x753,
0x7531, 0x7532, 0x75321, 0x754, 0x7541, 0x7542, 0x75421, 0x7543, 0x75431,
0x75432, 0x754321, 0x76, 0x761, 0x762, 0x7621, 0x763, 0x7631, 0x7632,
0x76321, 0x764, 0x7641, 0x7642, 0x76421, 0x7643, 0x76431, 0x76432, 0x764321,
0x765, 0x7651, 0x7652, 0x76521, 0x7653, 0x76531, 0x76532, 0x765321, 0x7654,
0x76541, 0x76542, 0x765421, 0x76543, 0x765431, 0x765432, 0x7654321, 0x8,
0x81, 0x82, 0x821, 0x83, 0x831, 0x832, 0x8321, 0x84, 0x841, 0x842, 0x8421,
0x843, 0x8431, 0x8432, 0x84321, 0x85, 0x851, 0x852, 0x8521, 0x853, 0x8531,
0x8532, 0x85321, 0x854, 0x8541, 0x8542, 0x85421, 0x8543, 0x85431, 0x85432,
0x854321, 0x86, 0x861, 0x862, 0x8621, 0x863, 0x8631, 0x8632, 0x86321, 0x864,
0x8641, 0x8642, 0x86421, 0x8643, 0x86431, 0x86432, 0x864321, 0x865, 0x8651,
0x8652, 0x86521, 0x8653, 0x86531, 0x86532, 0x865321, 0x8654, 0x86541,
0x86542, 0x865421, 0x86543, 0x865431, 0x865432, 0x8654321, 0x87, 0x871,
0x872, 0x8721, 0x873, 0x8731, 0x8732, 0x87321, 0x874, 0x8741, 0x8742,
0x87421, 0x8743, 0x87431, 0x87432, 0x874321, 0x875, 0x8751, 0x8752, 0x87521,
0x8753, 0x87531, 0x87532, 0x875321, 0x8754, 0x87541, 0x87542, 0x875421,
0x87543, 0x875431, 0x875432, 0x8754321, 0x876, 0x8761, 0x8762, 0x87621,
0x8763, 0x87631, 0x87632, 0x876321, 0x8764, 0x87641, 0x87642, 0x876421,
0x87643, 0x876431, 0x876432, 0x8764321, 0x8765, 0x87651, 0x87652, 0x876521,
0x87653, 0x876531, 0x876532, 0x8765321, 0x87654, 0x876541, 0x876542,
0x8765421, 0x876543, 0x8765431, 0x8765432, 0x87654321
};
/***** the python code that generated bitlist
def bits2int(val):
arr=0
for shift in range(8,0,-1):
if val & 0x80:
arr = (arr << 4) | shift
val = val << 1
return arr
def int_table():
tbl = [ hex(bits2int(val)).strip('L') for val in range(256) ]
return ','.join(tbl)
******/
// hmmm, what about an iterator that finds zeros though,
// or a reverse iterator... should they be separate classes
// for efficiency, or have a common root interface? (or
// maybe both? could ask for a SetBitsIterator, etc...
private final long[] arr;
private final int words;
private int i=-1;
private long word;
private int wordShift;
private int indexArray;
private int curDocId = -1;
public OpenBitSetIterator(OpenBitSet obs) {
this(obs.getBits(), obs.getNumWords());
}
public OpenBitSetIterator(long[] bits, int numWords) {
arr = bits;
words = numWords;
}
// 64 bit shifts
private void shift() {
if ((int)word ==0) {wordShift +=32; word = word >>>32; }
if ((word & 0x0000FFFF) == 0) { wordShift +=16; word >>>=16; }
if ((word & 0x000000FF) == 0) { wordShift +=8; word >>>=8; }
indexArray = bitlist[(int)word & 0xff];
}
/***** alternate shift implementations
// 32 bit shifts, but a long shift needed at the end
private void shift2() {
int y = (int)word;
if (y==0) {wordShift +=32; y = (int)(word >>>32); }
if ((y & 0x0000FFFF) == 0) { wordShift +=16; y>>>=16; }
if ((y & 0x000000FF) == 0) { wordShift +=8; y>>>=8; }
indexArray = bitlist[y & 0xff];
word >>>= (wordShift +1);
}
private void shift3() {
int lower = (int)word;
int lowByte = lower & 0xff;
if (lowByte != 0) {
indexArray=bitlist[lowByte];
return;
}
shift();
}
******/
@Override
public int nextDoc() {
if (indexArray == 0) {
if (word != 0) {
word >>>= 8;
wordShift += 8;
}
while (word == 0) {
if (++i >= words) {
return curDocId = NO_MORE_DOCS;
}
word = arr[i];
wordShift = -1; // loop invariant code motion should move this
}
// after the first time, should I go with a linear search, or
// stick with the binary search in shift?
shift();
}
int bitIndex = (indexArray & 0x0f) + wordShift;
indexArray >>>= 4;
// should i<<6 be cached as a separate variable?
// it would only save one cycle in the best circumstances.
return curDocId = (i<<6) + bitIndex;
}
@Override
public int advance(int target) {
indexArray = 0;
i = target >> 6;
if (i >= words) {
word = 0; // setup so next() will also return -1
return curDocId = NO_MORE_DOCS;
}
wordShift = target & 0x3f;
word = arr[i] >>> wordShift;
if (word != 0) {
wordShift--; // compensate for 1 based arrIndex
} else {
while (word == 0) {
if (++i >= words) {
return curDocId = NO_MORE_DOCS;
}
word = arr[i];
}
wordShift = -1;
}
shift();
int bitIndex = (indexArray & 0x0f) + wordShift;
indexArray >>>= 4;
// should i<<6 be cached as a separate variable?
// it would only save one cycle in the best circumstances.
return curDocId = (i<<6) + bitIndex;
}
@Override
public int docID() {
return curDocId;
}
}