2
* Licensed to the Apache Software Foundation (ASF) under one or more
3
* contributor license agreements. See the NOTICE file distributed with
4
* this work for additional information regarding copyright ownership.
5
* The ASF licenses this file to You under the Apache License, Version 2.0
6
* (the "License"); you may not use this file except in compliance with
7
* the License. You may obtain a copy of the License at
9
* http://www.apache.org/licenses/LICENSE-2.0
11
* Unless required by applicable law or agreed to in writing, software
12
* distributed under the License is distributed on an "AS IS" BASIS,
13
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14
* See the License for the specific language governing permissions and
15
* limitations under the License.
18
package org.apache.lucene.util;
20
import java.util.Arrays;
21
import java.io.Serializable;
23
import org.apache.lucene.search.DocIdSet;
24
import org.apache.lucene.search.DocIdSetIterator;
26
/** An "open" BitSet implementation that allows direct access to the array of words
29
* Unlike java.util.bitset, the fact that bits are packed into an array of longs
30
* is part of the interface. This allows efficient implementation of other algorithms
31
* by someone other than the author. It also allows one to efficiently implement
32
* alternate serialization or interchange formats.
34
* <code>OpenBitSet</code> is faster than <code>java.util.BitSet</code> in most operations
35
* and *much* faster at calculating cardinality of sets and results of set operations.
36
* It can also handle sets of larger cardinality (up to 64 * 2**32-1)
38
* The goals of <code>OpenBitSet</code> are the fastest implementation possible, and
39
* maximum code reuse. Extra safety and encapsulation
40
* may always be built on top, but if that's built in, the cost can never be removed (and
41
* hence people re-implement their own version in order to get better performance).
42
* If you want a "safe", totally encapsulated (and slower and limited) BitSet
43
* class, use <code>java.util.BitSet</code>.
45
* <h3>Performance Results</h3>
47
Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M
48
<br/>BitSet size = 1,000,000
49
<br/>Results are java.util.BitSet time divided by OpenBitSet time.
52
<th></th> <th>cardinality</th> <th>intersect_count</th> <th>union</th> <th>nextSetBit</th> <th>get</th> <th>iterator</th>
55
<th>50% full</th> <td>3.36</td> <td>3.96</td> <td>1.44</td> <td>1.46</td> <td>1.99</td> <td>1.58</td>
58
<th>1% full</th> <td>3.31</td> <td>3.90</td> <td> </td> <td>1.04</td> <td> </td> <td>0.99</td>
62
Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06 -server -Xbatch -Xmx64M
63
<br/>BitSet size = 1,000,000
64
<br/>Results are java.util.BitSet time divided by OpenBitSet time.
67
<th></th> <th>cardinality</th> <th>intersect_count</th> <th>union</th> <th>nextSetBit</th> <th>get</th> <th>iterator</th>
70
<th>50% full</th> <td>2.50</td> <td>3.50</td> <td>1.00</td> <td>1.03</td> <td>1.12</td> <td>1.25</td>
73
<th>1% full</th> <td>2.51</td> <td>3.49</td> <td> </td> <td>1.00</td> <td> </td> <td>1.02</td>
78
public class OpenBitSet extends DocIdSet implements Cloneable, Serializable, Bits {
79
protected long[] bits;
80
protected int wlen; // number of words (elements) used in the array
82
// Used only for assert:
85
/** Constructs an OpenBitSet large enough to hold numBits.
89
public OpenBitSet(long numBits) {
90
this.numBits = numBits;
91
bits = new long[bits2words(numBits)];
99
/** Constructs an OpenBitSet from an existing long[].
101
* The first 64 bits are in long[0],
102
* with bit index 0 at the least significant bit, and bit index 63 at the most significant.
104
* the word containing it is long[index/64], and it is at bit number index%64 within that word.
106
* numWords are the number of elements in the array that contain
107
* set bits (non-zero longs).
108
* numWords should be <= bits.length, and
109
* any existing words in the array at position >= numWords should be zero.
112
public OpenBitSet(long[] bits, int numWords) {
114
this.wlen = numWords;
115
this.numBits = wlen * 64;
119
public DocIdSetIterator iterator() {
120
return new OpenBitSetIterator(bits, wlen);
123
/** This DocIdSet implementation is cacheable. */
125
public boolean isCacheable() {
129
/** Returns the current capacity in bits (1 greater than the index of the last bit) */
130
public long capacity() { return bits.length << 6; }
133
* Returns the current capacity of this set. Included for
134
* compatibility. This is *not* equal to {@link #cardinality}
140
public int length() {
141
return bits.length << 6;
144
/** Returns true if there are no set bits */
145
public boolean isEmpty() { return cardinality()==0; }
147
/** Expert: returns the long[] storing the bits */
148
public long[] getBits() { return bits; }
150
/** Expert: sets a new long[] to use as the bit storage */
151
public void setBits(long[] bits) { this.bits = bits; }
153
/** Expert: gets the number of longs in the array that are in use */
154
public int getNumWords() { return wlen; }
156
/** Expert: sets the number of longs in the array that are in use */
157
public void setNumWords(int nWords) { this.wlen=nWords; }
161
/** Returns true or false for the specified bit index. */
162
public boolean get(int index) {
163
int i = index >> 6; // div 64
164
// signed shift will keep a negative index and force an
165
// array-index-out-of-bounds-exception, removing the need for an explicit check.
166
if (i>=bits.length) return false;
168
int bit = index & 0x3f; // mod 64
169
long bitmask = 1L << bit;
170
return (bits[i] & bitmask) != 0;
174
/** Returns true or false for the specified bit index.
175
* The index should be less than the OpenBitSet size
177
public boolean fastGet(int index) {
178
assert index >= 0 && index < numBits;
179
int i = index >> 6; // div 64
180
// signed shift will keep a negative index and force an
181
// array-index-out-of-bounds-exception, removing the need for an explicit check.
182
int bit = index & 0x3f; // mod 64
183
long bitmask = 1L << bit;
184
return (bits[i] & bitmask) != 0;
189
/** Returns true or false for the specified bit index
191
public boolean get(long index) {
192
int i = (int)(index >> 6); // div 64
193
if (i>=bits.length) return false;
194
int bit = (int)index & 0x3f; // mod 64
195
long bitmask = 1L << bit;
196
return (bits[i] & bitmask) != 0;
199
/** Returns true or false for the specified bit index.
200
* The index should be less than the OpenBitSet size.
202
public boolean fastGet(long index) {
203
assert index >= 0 && index < numBits;
204
int i = (int)(index >> 6); // div 64
205
int bit = (int)index & 0x3f; // mod 64
206
long bitmask = 1L << bit;
207
return (bits[i] & bitmask) != 0;
211
// alternate implementation of get()
212
public boolean get1(int index) {
213
int i = index >> 6; // div 64
214
int bit = index & 0x3f; // mod 64
215
return ((bits[i]>>>bit) & 0x01) != 0;
216
// this does a long shift and a bittest (on x86) vs
217
// a long shift, and a long AND, (the test for zero is prob a no-op)
218
// testing on a P4 indicates this is slower than (bits[i] & bitmask) != 0;
223
/** returns 1 if the bit is set, 0 if not.
224
* The index should be less than the OpenBitSet size
226
public int getBit(int index) {
227
assert index >= 0 && index < numBits;
228
int i = index >> 6; // div 64
229
int bit = index & 0x3f; // mod 64
230
return ((int)(bits[i]>>>bit)) & 0x01;
235
public boolean get2(int index) {
236
int word = index >> 6; // div 64
237
int bit = index & 0x0000003f; // mod 64
238
return (bits[word] << bit) < 0; // hmmm, this would work if bit order were reversed
239
// we could right shift and check for parity bit, if it was available to us.
243
/** sets a bit, expanding the set size if necessary */
244
public void set(long index) {
245
int wordNum = expandingWordNum(index);
246
int bit = (int)index & 0x3f;
247
long bitmask = 1L << bit;
248
bits[wordNum] |= bitmask;
252
/** Sets the bit at the specified index.
253
* The index should be less than the OpenBitSet size.
255
public void fastSet(int index) {
256
assert index >= 0 && index < numBits;
257
int wordNum = index >> 6; // div 64
258
int bit = index & 0x3f; // mod 64
259
long bitmask = 1L << bit;
260
bits[wordNum] |= bitmask;
263
/** Sets the bit at the specified index.
264
* The index should be less than the OpenBitSet size.
266
public void fastSet(long index) {
267
assert index >= 0 && index < numBits;
268
int wordNum = (int)(index >> 6);
269
int bit = (int)index & 0x3f;
270
long bitmask = 1L << bit;
271
bits[wordNum] |= bitmask;
274
/** Sets a range of bits, expanding the set size if necessary
276
* @param startIndex lower index
277
* @param endIndex one-past the last bit to set
279
public void set(long startIndex, long endIndex) {
280
if (endIndex <= startIndex) return;
282
int startWord = (int)(startIndex>>6);
284
// since endIndex is one past the end, this is index of the last
285
// word to be changed.
286
int endWord = expandingWordNum(endIndex-1);
288
long startmask = -1L << startIndex;
289
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
291
if (startWord == endWord) {
292
bits[startWord] |= (startmask & endmask);
296
bits[startWord] |= startmask;
297
Arrays.fill(bits, startWord+1, endWord, -1L);
298
bits[endWord] |= endmask;
303
protected int expandingWordNum(long index) {
304
int wordNum = (int)(index >> 6);
306
ensureCapacity(index+1);
309
assert (numBits = Math.max(numBits, index+1)) >= 0;
315
* The index should be less than the OpenBitSet size.
317
public void fastClear(int index) {
318
assert index >= 0 && index < numBits;
319
int wordNum = index >> 6;
320
int bit = index & 0x03f;
321
long bitmask = 1L << bit;
322
bits[wordNum] &= ~bitmask;
323
// hmmm, it takes one more instruction to clear than it does to set... any
324
// way to work around this? If there were only 63 bits per word, we could
325
// use a right shift of 10111111...111 in binary to position the 0 in the
326
// correct place (using sign extension).
327
// Could also use Long.rotateRight() or rotateLeft() *if* they were converted
328
// by the JVM into a native instruction.
329
// bits[word] &= Long.rotateLeft(0xfffffffe,bit);
333
* The index should be less than the OpenBitSet size.
335
public void fastClear(long index) {
336
assert index >= 0 && index < numBits;
337
int wordNum = (int)(index >> 6); // div 64
338
int bit = (int)index & 0x3f; // mod 64
339
long bitmask = 1L << bit;
340
bits[wordNum] &= ~bitmask;
343
/** clears a bit, allowing access beyond the current set size without changing the size.*/
344
public void clear(long index) {
345
int wordNum = (int)(index >> 6); // div 64
346
if (wordNum>=wlen) return;
347
int bit = (int)index & 0x3f; // mod 64
348
long bitmask = 1L << bit;
349
bits[wordNum] &= ~bitmask;
352
/** Clears a range of bits. Clearing past the end does not change the size of the set.
354
* @param startIndex lower index
355
* @param endIndex one-past the last bit to clear
357
public void clear(int startIndex, int endIndex) {
358
if (endIndex <= startIndex) return;
360
int startWord = (startIndex>>6);
361
if (startWord >= wlen) return;
363
// since endIndex is one past the end, this is index of the last
364
// word to be changed.
365
int endWord = ((endIndex-1)>>6);
367
long startmask = -1L << startIndex;
368
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
370
// invert masks since we are clearing
371
startmask = ~startmask;
374
if (startWord == endWord) {
375
bits[startWord] &= (startmask | endmask);
379
bits[startWord] &= startmask;
381
int middle = Math.min(wlen, endWord);
382
Arrays.fill(bits, startWord+1, middle, 0L);
383
if (endWord < wlen) {
384
bits[endWord] &= endmask;
389
/** Clears a range of bits. Clearing past the end does not change the size of the set.
391
* @param startIndex lower index
392
* @param endIndex one-past the last bit to clear
394
public void clear(long startIndex, long endIndex) {
395
if (endIndex <= startIndex) return;
397
int startWord = (int)(startIndex>>6);
398
if (startWord >= wlen) return;
400
// since endIndex is one past the end, this is index of the last
401
// word to be changed.
402
int endWord = (int)((endIndex-1)>>6);
404
long startmask = -1L << startIndex;
405
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
407
// invert masks since we are clearing
408
startmask = ~startmask;
411
if (startWord == endWord) {
412
bits[startWord] &= (startmask | endmask);
416
bits[startWord] &= startmask;
418
int middle = Math.min(wlen, endWord);
419
Arrays.fill(bits, startWord+1, middle, 0L);
420
if (endWord < wlen) {
421
bits[endWord] &= endmask;
427
/** Sets a bit and returns the previous value.
428
* The index should be less than the OpenBitSet size.
430
public boolean getAndSet(int index) {
431
assert index >= 0 && index < numBits;
432
int wordNum = index >> 6; // div 64
433
int bit = index & 0x3f; // mod 64
434
long bitmask = 1L << bit;
435
boolean val = (bits[wordNum] & bitmask) != 0;
436
bits[wordNum] |= bitmask;
440
/** Sets a bit and returns the previous value.
441
* The index should be less than the OpenBitSet size.
443
public boolean getAndSet(long index) {
444
assert index >= 0 && index < numBits;
445
int wordNum = (int)(index >> 6); // div 64
446
int bit = (int)index & 0x3f; // mod 64
447
long bitmask = 1L << bit;
448
boolean val = (bits[wordNum] & bitmask) != 0;
449
bits[wordNum] |= bitmask;
454
* The index should be less than the OpenBitSet size.
456
public void fastFlip(int index) {
457
assert index >= 0 && index < numBits;
458
int wordNum = index >> 6; // div 64
459
int bit = index & 0x3f; // mod 64
460
long bitmask = 1L << bit;
461
bits[wordNum] ^= bitmask;
465
* The index should be less than the OpenBitSet size.
467
public void fastFlip(long index) {
468
assert index >= 0 && index < numBits;
469
int wordNum = (int)(index >> 6); // div 64
470
int bit = (int)index & 0x3f; // mod 64
471
long bitmask = 1L << bit;
472
bits[wordNum] ^= bitmask;
475
/** flips a bit, expanding the set size if necessary */
476
public void flip(long index) {
477
int wordNum = expandingWordNum(index);
478
int bit = (int)index & 0x3f; // mod 64
479
long bitmask = 1L << bit;
480
bits[wordNum] ^= bitmask;
483
/** flips a bit and returns the resulting bit value.
484
* The index should be less than the OpenBitSet size.
486
public boolean flipAndGet(int index) {
487
assert index >= 0 && index < numBits;
488
int wordNum = index >> 6; // div 64
489
int bit = index & 0x3f; // mod 64
490
long bitmask = 1L << bit;
491
bits[wordNum] ^= bitmask;
492
return (bits[wordNum] & bitmask) != 0;
495
/** flips a bit and returns the resulting bit value.
496
* The index should be less than the OpenBitSet size.
498
public boolean flipAndGet(long index) {
499
assert index >= 0 && index < numBits;
500
int wordNum = (int)(index >> 6); // div 64
501
int bit = (int)index & 0x3f; // mod 64
502
long bitmask = 1L << bit;
503
bits[wordNum] ^= bitmask;
504
return (bits[wordNum] & bitmask) != 0;
507
/** Flips a range of bits, expanding the set size if necessary
509
* @param startIndex lower index
510
* @param endIndex one-past the last bit to flip
512
public void flip(long startIndex, long endIndex) {
513
if (endIndex <= startIndex) return;
514
int startWord = (int)(startIndex>>6);
516
// since endIndex is one past the end, this is index of the last
517
// word to be changed.
518
int endWord = expandingWordNum(endIndex-1);
520
/*** Grrr, java shifting wraps around so -1L>>>64 == -1
521
* for that reason, make sure not to use endmask if the bits to flip will
522
* be zero in the last word (redefine endWord to be the last changed...)
523
long startmask = -1L << (startIndex & 0x3f); // example: 11111...111000
524
long endmask = -1L >>> (64-(endIndex & 0x3f)); // example: 00111...111111
527
long startmask = -1L << startIndex;
528
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
530
if (startWord == endWord) {
531
bits[startWord] ^= (startmask & endmask);
535
bits[startWord] ^= startmask;
537
for (int i=startWord+1; i<endWord; i++) {
541
bits[endWord] ^= endmask;
546
public static int pop(long v0, long v1, long v2, long v3) {
547
// derived from pop_array by setting last four elems to 0.
548
// exchanges one pop() call for 10 elementary operations
549
// saving about 7 instructions... is there a better way?
554
long twosB =(ones&v2)|(u2&v3);
557
long fours=(twosA&twosB);
558
long twos=twosA^twosB;
560
return (pop(fours)<<2)
568
/** @return the number of set bits */
569
public long cardinality() {
570
return BitUtil.pop_array(bits,0,wlen);
573
/** Returns the popcount or cardinality of the intersection of the two sets.
574
* Neither set is modified.
576
public static long intersectionCount(OpenBitSet a, OpenBitSet b) {
577
return BitUtil.pop_intersect(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
580
/** Returns the popcount or cardinality of the union of the two sets.
581
* Neither set is modified.
583
public static long unionCount(OpenBitSet a, OpenBitSet b) {
584
long tot = BitUtil.pop_union(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
585
if (a.wlen < b.wlen) {
586
tot += BitUtil.pop_array(b.bits, a.wlen, b.wlen-a.wlen);
587
} else if (a.wlen > b.wlen) {
588
tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen-b.wlen);
593
/** Returns the popcount or cardinality of "a and not b"
594
* or "intersection(a, not(b))".
595
* Neither set is modified.
597
public static long andNotCount(OpenBitSet a, OpenBitSet b) {
598
long tot = BitUtil.pop_andnot(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
599
if (a.wlen > b.wlen) {
600
tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen-b.wlen);
605
/** Returns the popcount or cardinality of the exclusive-or of the two sets.
606
* Neither set is modified.
608
public static long xorCount(OpenBitSet a, OpenBitSet b) {
609
long tot = BitUtil.pop_xor(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
610
if (a.wlen < b.wlen) {
611
tot += BitUtil.pop_array(b.bits, a.wlen, b.wlen-a.wlen);
612
} else if (a.wlen > b.wlen) {
613
tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen-b.wlen);
619
/** Returns the index of the first set bit starting at the index specified.
620
* -1 is returned if there are no more set bits.
622
public int nextSetBit(int index) {
624
if (i>=wlen) return -1;
625
int subIndex = index & 0x3f; // index within the word
626
long word = bits[i] >> subIndex; // skip all the bits to the right of index
629
return (i<<6) + subIndex + BitUtil.ntz(word);
634
if (word!=0) return (i<<6) + BitUtil.ntz(word);
640
/** Returns the index of the first set bit starting at the index specified.
641
* -1 is returned if there are no more set bits.
643
public long nextSetBit(long index) {
644
int i = (int)(index>>>6);
645
if (i>=wlen) return -1;
646
int subIndex = (int)index & 0x3f; // index within the word
647
long word = bits[i] >>> subIndex; // skip all the bits to the right of index
650
return (((long)i)<<6) + (subIndex + BitUtil.ntz(word));
655
if (word!=0) return (((long)i)<<6) + BitUtil.ntz(word);
662
/** Returns the index of the first set bit starting downwards at
663
* the index specified.
664
* -1 is returned if there are no more set bits.
666
public int prevSetBit(int index) {
672
if (i < 0) return -1;
673
subIndex = 63; // last possible bit
676
if (i < 0) return -1;
677
subIndex = index & 0x3f; // index within the word
678
word = (bits[i] << (63-subIndex)); // skip all the bits to the left of index
682
return (i << 6) + subIndex - Long.numberOfLeadingZeros(word); // See LUCENE-3197
688
return (i << 6) + 63 - Long.numberOfLeadingZeros(word);
695
/** Returns the index of the first set bit starting downwards at
696
* the index specified.
697
* -1 is returned if there are no more set bits.
699
public long prevSetBit(long index) {
700
int i = (int) (index >> 6);
705
if (i < 0) return -1;
706
subIndex = 63; // last possible bit
709
if (i < 0) return -1;
710
subIndex = (int)index & 0x3f; // index within the word
711
word = (bits[i] << (63-subIndex)); // skip all the bits to the left of index
715
return (((long)i)<<6) + subIndex - Long.numberOfLeadingZeros(word); // See LUCENE-3197
721
return (((long)i)<<6) + 63 - Long.numberOfLeadingZeros(word);
729
public Object clone() {
731
OpenBitSet obs = (OpenBitSet)super.clone();
732
obs.bits = obs.bits.clone(); // hopefully an array clone is as fast(er) than arraycopy
734
} catch (CloneNotSupportedException e) {
735
throw new RuntimeException(e);
739
/** this = this AND other */
740
public void intersect(OpenBitSet other) {
741
int newLen= Math.min(this.wlen,other.wlen);
742
long[] thisArr = this.bits;
743
long[] otherArr = other.bits;
744
// testing against zero can be more efficient
747
thisArr[pos] &= otherArr[pos];
749
if (this.wlen > newLen) {
750
// fill zeros from the new shorter length to the old length
751
Arrays.fill(bits,newLen,this.wlen,0);
756
/** this = this OR other */
757
public void union(OpenBitSet other) {
758
int newLen = Math.max(wlen,other.wlen);
759
ensureCapacityWords(newLen);
760
assert (numBits = Math.max(other.numBits, numBits)) >= 0;
762
long[] thisArr = this.bits;
763
long[] otherArr = other.bits;
764
int pos=Math.min(wlen,other.wlen);
766
thisArr[pos] |= otherArr[pos];
768
if (this.wlen < newLen) {
769
System.arraycopy(otherArr, this.wlen, thisArr, this.wlen, newLen-this.wlen);
775
/** Remove all elements set in other. this = this AND_NOT other */
776
public void remove(OpenBitSet other) {
777
int idx = Math.min(wlen,other.wlen);
778
long[] thisArr = this.bits;
779
long[] otherArr = other.bits;
781
thisArr[idx] &= ~otherArr[idx];
785
/** this = this XOR other */
786
public void xor(OpenBitSet other) {
787
int newLen = Math.max(wlen,other.wlen);
788
ensureCapacityWords(newLen);
789
assert (numBits = Math.max(other.numBits, numBits)) >= 0;
791
long[] thisArr = this.bits;
792
long[] otherArr = other.bits;
793
int pos=Math.min(wlen,other.wlen);
795
thisArr[pos] ^= otherArr[pos];
797
if (this.wlen < newLen) {
798
System.arraycopy(otherArr, this.wlen, thisArr, this.wlen, newLen-this.wlen);
804
// some BitSet compatability methods
806
//** see {@link intersect} */
807
public void and(OpenBitSet other) {
811
//** see {@link union} */
812
public void or(OpenBitSet other) {
816
//** see {@link andNot} */
817
public void andNot(OpenBitSet other) {
821
/** returns true if the sets have any elements in common */
822
public boolean intersects(OpenBitSet other) {
823
int pos = Math.min(this.wlen, other.wlen);
824
long[] thisArr = this.bits;
825
long[] otherArr = other.bits;
827
if ((thisArr[pos] & otherArr[pos])!=0) return true;
834
/** Expand the long[] with the size given as a number of words (64 bit longs).
835
* getNumWords() is unchanged by this call.
837
public void ensureCapacityWords(int numWords) {
838
if (bits.length < numWords) {
839
bits = ArrayUtil.grow(bits, numWords);
843
/** Ensure that the long[] is big enough to hold numBits, expanding it if necessary.
844
* getNumWords() is unchanged by this call.
846
public void ensureCapacity(long numBits) {
847
ensureCapacityWords(bits2words(numBits));
850
/** Lowers numWords, the number of words in use,
851
* by checking for trailing zero words.
853
public void trimTrailingZeros() {
855
while (idx>=0 && bits[idx]==0) idx--;
859
/** returns the number of 64 bit words it would take to hold numBits */
860
public static int bits2words(long numBits) {
861
return (int)(((numBits-1)>>>6)+1);
865
/** returns true if both sets have the same bits set */
867
public boolean equals(Object o) {
868
if (this == o) return true;
869
if (!(o instanceof OpenBitSet)) return false;
871
OpenBitSet b = (OpenBitSet)o;
872
// make a the larger set.
873
if (b.wlen > this.wlen) {
879
// check for any set bits out of the range of b
880
for (int i=a.wlen-1; i>=b.wlen; i--) {
881
if (a.bits[i]!=0) return false;
884
for (int i=b.wlen-1; i>=0; i--) {
885
if (a.bits[i] != b.bits[i]) return false;
893
public int hashCode() {
894
// Start with a zero hash and use a mix that results in zero if the input is zero.
895
// This effectively truncates trailing zeros without an explicit check.
897
for (int i = bits.length; --i>=0;) {
899
h = (h << 1) | (h >>> 63); // rotate left
901
// fold leftmost bits into right and add a constant to prevent
902
// empty sets from returning 0, which is too common.
903
return (int)((h>>32) ^ h) + 0x98761234;