OpenBitSet.cs

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 * 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
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 */

using System;
using Lucene.Net.Support;
using DocIdSet = Lucene.Net.Search.DocIdSet;
using DocIdSetIterator = Lucene.Net.Search.DocIdSetIterator;

namespace Lucene.Net.Util
{
    
    /// <summary>An "open" BitSet implementation that allows direct access to the array of words
    /// storing the bits.
    /// <p/>
    /// Unlike java.util.bitset, the fact that bits are packed into an array of longs
    /// is part of the interface.  This allows efficient implementation of other algorithms
    /// by someone other than the author.  It also allows one to efficiently implement
    /// alternate serialization or interchange formats.
    /// <p/>
    /// <c>OpenBitSet</c> is faster than <c>java.util.BitSet</c> in most operations
    /// and *much* faster at calculating cardinality of sets and results of set operations.
    /// It can also handle sets of larger cardinality (up to 64 * 2**32-1)
    /// <p/>
    /// The goals of <c>OpenBitSet</c> are the fastest implementation possible, and
    /// maximum code reuse.  Extra safety and encapsulation
    /// may always be built on top, but if that's built in, the cost can never be removed (and
    /// hence people re-implement their own version in order to get better performance).
    /// If you want a "safe", totally encapsulated (and slower and limited) BitSet
    /// class, use <c>java.util.BitSet</c>.
    /// <p/>
    /// <h3>Performance Results</h3>
    /// 
    /// Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M
    /// <br/>BitSet size = 1,000,000
    /// <br/>Results are java.util.BitSet time divided by OpenBitSet time.
    /// <table border="1">
    /// <tr>
    /// <th></th> <th>cardinality</th> <th>intersect_count</th> <th>union</th> <th>nextSetBit</th> <th>get</th> <th>iterator</th>
    /// </tr>
    /// <tr>
    /// <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>
    /// </tr>
    /// <tr>
    /// <th>1% full</th> <td>3.31</td> <td>3.90</td> <td>&#160;</td> <td>1.04</td> <td>&#160;</td> <td>0.99</td>
    /// </tr>
    /// </table>
    /// <br/>
    /// Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06 -server -Xbatch -Xmx64M
    /// <br/>BitSet size = 1,000,000
    /// <br/>Results are java.util.BitSet time divided by OpenBitSet time.
    /// <table border="1">
    /// <tr>
    /// <th></th> <th>cardinality</th> <th>intersect_count</th> <th>union</th> <th>nextSetBit</th> <th>get</th> <th>iterator</th>
    /// </tr>
    /// <tr>
    /// <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>
    /// </tr>
    /// <tr>
    /// <th>1% full</th> <td>2.51</td> <td>3.49</td> <td>&#160;</td> <td>1.00</td> <td>&#160;</td> <td>1.02</td>
    /// </tr>
    /// </table>
    /// </summary>
    /// <version>  $Id$
    /// </version>
    
    [Serializable]
    public class OpenBitSet:DocIdSet, System.ICloneable
    {
        protected internal long[] internalbits;
        protected internal int wlen; // number of words (elements) used in the array
        
        /// <summary>Constructs an OpenBitSet large enough to hold numBits.
        /// 
        /// </summary>
        /// <param name="numBits">
        /// </param>
        public OpenBitSet(long numBits)
        {
            internalbits = new long[Bits2words(numBits)];
            wlen = internalbits.Length;
        }
        
        public OpenBitSet():this(64)
        {
        }
        
        /// <summary>Constructs an OpenBitSet from an existing long[].
        /// <br/>
        /// The first 64 bits are in long[0],
        /// with bit index 0 at the least significant bit, and bit index 63 at the most significant.
        /// Given a bit index,
        /// the word containing it is long[index/64], and it is at bit number index%64 within that word.
        /// <p/>
        /// numWords are the number of elements in the array that contain
        /// set bits (non-zero longs).
        /// numWords should be &lt;= bits.length, and
        /// any existing words in the array at position &gt;= numWords should be zero.
        /// 
        /// </summary>
        public OpenBitSet(long[] bits, int numWords)
        {
            this.internalbits = bits;
            this.wlen = numWords;
        }
        
        public override DocIdSetIterator Iterator()
        {
            return new OpenBitSetIterator(internalbits, wlen);
        }

        /// <summary>This DocIdSet implementation is cacheable. </summary>
        public override bool IsCacheable
        {
            get { return true; }
        }

        /// <summary>Returns the current capacity in bits (1 greater than the index of the last bit) </summary>
        public virtual long Capacity()
        {
            return internalbits.Length << 6;
        }
        
        /// <summary> Returns the current capacity of this set.  Included for
        /// compatibility.  This is *not* equal to <see cref="Cardinality" />
        /// </summary>
        public virtual long Size()
        {
            return Capacity();
        }
        
        /// <summary>Returns true if there are no set bits </summary>
        public virtual bool IsEmpty()
        {
            return Cardinality() == 0;
        }

        /// <summary>Expert: Gets or sets the long[] storing the bits </summary>
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays")]
        public virtual long[] Bits
        {
            set { this.internalbits = value; }
            get { return internalbits; }
        }

        /// <summary>Expert: gets or sets the number of longs in the array that are in use </summary>
        public virtual int NumWords
        {
            get { return wlen; }
            set { this.wlen = value; }
        }


        /// <summary>Returns true or false for the specified bit index. </summary>
        public virtual bool Get(int index)
        {
            int i = index >> 6; // div 64
            // signed shift will keep a negative index and force an
            // array-index-out-of-bounds-exception, removing the need for an explicit check.
            if (i >= internalbits.Length)
                return false;
            
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            return (internalbits[i] & bitmask) != 0;
        }
        
        
        /// <summary>Returns true or false for the specified bit index.
        /// The index should be less than the OpenBitSet size
        /// </summary>
        public virtual bool FastGet(int index)
        {
            int i = index >> 6; // div 64
            // signed shift will keep a negative index and force an
            // array-index-out-of-bounds-exception, removing the need for an explicit check.
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            return (internalbits[i] & bitmask) != 0;
        }
        
        
        
        /// <summary>Returns true or false for the specified bit index</summary>
        public virtual bool Get(long index)
        {
            int i = (int) (index >> 6); // div 64
            if (i >= internalbits.Length)
                return false;
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            return (internalbits[i] & bitmask) != 0;
        }
        
        /// <summary>Returns true or false for the specified bit index.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual bool FastGet(long index)
        {
            int i = (int) (index >> 6); // div 64
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            return (internalbits[i] & bitmask) != 0;
        }
        
        /*
        // alternate implementation of get()
        public boolean get1(int index) {
        int i = index >> 6;                // div 64
        int bit = index & 0x3f;            // mod 64
        return ((bits[i]>>>bit) & 0x01) != 0;
        // this does a long shift and a bittest (on x86) vs
        // a long shift, and a long AND, (the test for zero is prob a no-op)
        // testing on a P4 indicates this is slower than (bits[i] & bitmask) != 0;
        }
        */
        
        
        /// <summary>returns 1 if the bit is set, 0 if not.
        /// The index should be less than the OpenBitSet size
        /// </summary>
        public virtual int GetBit(int index)
        {
            int i = index >> 6; // div 64
            int bit = index & 0x3f; // mod 64
            return ((int )((ulong) (internalbits[i]) >> bit)) & 0x01;
        }
        
        
        /*
        public boolean get2(int index) {
        int word = index >> 6;            // div 64
        int bit = index & 0x0000003f;     // mod 64
        return (bits[word] << bit) < 0;   // hmmm, this would work if bit order were reversed
        // we could right shift and check for parity bit, if it was available to us.
        }
        */
        
        /// <summary>sets a bit, expanding the set size if necessary </summary>
        public virtual void  Set(long index)
        {
            int wordNum = ExpandingWordNum(index);
            int bit = (int) index & 0x3f;
            long bitmask = 1L << bit;
            internalbits[wordNum] |= bitmask;
        }
        
        
        /// <summary>Sets the bit at the specified index.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastSet(int index)
        {
            int wordNum = index >> 6; // div 64
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] |= bitmask;
        }
        
        /// <summary>Sets the bit at the specified index.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastSet(long index)
        {
            int wordNum = (int) (index >> 6);
            int bit = (int) index & 0x3f;
            long bitmask = 1L << bit;
            internalbits[wordNum] |= bitmask;
        }
        
        /// <summary>Sets a range of bits, expanding the set size if necessary
        /// 
        /// </summary>
        /// <param name="startIndex">lower index
        /// </param>
        /// <param name="endIndex">one-past the last bit to set
        /// </param>
        public virtual void  Set(long startIndex, long endIndex)
        {
            if (endIndex <= startIndex)
                return ;
            
            int startWord = (int) (startIndex >> 6);
            
            // since endIndex is one past the end, this is index of the last
            // word to be changed.
            int endWord = ExpandingWordNum(endIndex - 1);
            
            long startmask = - 1L << (int) startIndex;
            long endmask = (long) (0xffffffffffffffffUL >> (int) - endIndex); // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
            
            if (startWord == endWord)
            {
                internalbits[startWord] |= (startmask & endmask);
                return ;
            }
            
            internalbits[startWord] |= startmask;
            for (int i = startWord + 1; i < endWord; i++)
                internalbits[i] = -1L;
            internalbits[endWord] |= endmask;
        }



        protected internal virtual int ExpandingWordNum(long index)
        {
            int wordNum = (int) (index >> 6);
            if (wordNum >= wlen)
            {
                EnsureCapacity(index + 1);
                wlen = wordNum + 1;
            }
            return wordNum;
        }
        
        
        /// <summary>clears a bit.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastClear(int index)
        {
            int wordNum = index >> 6;
            int bit = index & 0x03f;
            long bitmask = 1L << bit;
            internalbits[wordNum] &= ~ bitmask;
            // hmmm, it takes one more instruction to clear than it does to set... any
            // way to work around this?  If there were only 63 bits per word, we could
            // use a right shift of 10111111...111 in binary to position the 0 in the
            // correct place (using sign extension).
            // Could also use Long.rotateRight() or rotateLeft() *if* they were converted
            // by the JVM into a native instruction.
            // bits[word] &= Long.rotateLeft(0xfffffffe,bit);
        }
        
        /// <summary>clears a bit.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastClear(long index)
        {
            int wordNum = (int) (index >> 6); // div 64
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] &= ~ bitmask;
        }
        
        /// <summary>clears a bit, allowing access beyond the current set size without changing the size.</summary>
        public virtual void  Clear(long index)
        {
            int wordNum = (int) (index >> 6); // div 64
            if (wordNum >= wlen)
                return ;
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] &= ~ bitmask;
        }
        
        /// <summary>Clears a range of bits.  Clearing past the end does not change the size of the set.
        /// 
        /// </summary>
        /// <param name="startIndex">lower index
        /// </param>
        /// <param name="endIndex">one-past the last bit to clear
        /// </param>
        public virtual void  Clear(int startIndex, int endIndex)
        {
            if (endIndex <= startIndex)
                return ;
            
            int startWord = (startIndex >> 6);
            if (startWord >= wlen)
                return ;
            
            // since endIndex is one past the end, this is index of the last
            // word to be changed.
            int endWord = ((endIndex - 1) >> 6);
            
            long startmask = - 1L << startIndex;
            long endmask = (long) (0xffffffffffffffffUL >> - endIndex); // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
            
            // invert masks since we are clearing
            startmask = ~ startmask;
            endmask = ~ endmask;
            
            if (startWord == endWord)
            {
                internalbits[startWord] &= (startmask | endmask);
                return ;
            }
            
            internalbits[startWord] &= startmask;
            
            int middle = System.Math.Min(wlen, endWord);
            for (int i = startWord + 1; i < middle; i++)
                internalbits[i] = 0L;
            if (endWord < wlen)
            {
                internalbits[endWord] &= endmask;
            }
        }
        
        
        /// <summary>Clears a range of bits.  Clearing past the end does not change the size of the set.
        /// 
        /// </summary>
        /// <param name="startIndex">lower index
        /// </param>
        /// <param name="endIndex">one-past the last bit to clear
        /// </param>
        public virtual void  Clear(long startIndex, long endIndex)
        {
            if (endIndex <= startIndex)
                return ;
            
            int startWord = (int) (startIndex >> 6);
            if (startWord >= wlen)
                return ;
            
            // since endIndex is one past the end, this is index of the last
            // word to be changed.
            int endWord = (int) ((endIndex - 1) >> 6);
            
            long startmask = - 1L << (int) startIndex;
            long endmask = (long) (0xffffffffffffffffUL >> (int) - endIndex); // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
            
            // invert masks since we are clearing
            startmask = ~ startmask;
            endmask = ~ endmask;
            
            if (startWord == endWord)
            {
                internalbits[startWord] &= (startmask | endmask);
                return ;
            }
            
            internalbits[startWord] &= startmask;
            
            int middle = System.Math.Min(wlen, endWord);
            for (int i = startWord + 1; i < middle; i++)
                internalbits[i] = 0L;
            if (endWord < wlen)
            {
                internalbits[endWord] &= endmask;
            }
        }
        
        
        
        /// <summary>Sets a bit and returns the previous value.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual bool GetAndSet(int index)
        {
            int wordNum = index >> 6; // div 64
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            bool val = (internalbits[wordNum] & bitmask) != 0;
            internalbits[wordNum] |= bitmask;
            return val;
        }
        
        /// <summary>Sets a bit and returns the previous value.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual bool GetAndSet(long index)
        {
            int wordNum = (int) (index >> 6); // div 64
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            bool val = (internalbits[wordNum] & bitmask) != 0;
            internalbits[wordNum] |= bitmask;
            return val;
        }
        
        /// <summary>flips a bit.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastFlip(int index)
        {
            int wordNum = index >> 6; // div 64
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] ^= bitmask;
        }
        
        /// <summary>flips a bit.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual void  FastFlip(long index)
        {
            int wordNum = (int) (index >> 6); // div 64
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] ^= bitmask;
        }
        
        /// <summary>flips a bit, expanding the set size if necessary </summary>
        public virtual void  Flip(long index)
        {
            int wordNum = ExpandingWordNum(index);
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] ^= bitmask;
        }
        
        /// <summary>flips a bit and returns the resulting bit value.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual bool FlipAndGet(int index)
        {
            int wordNum = index >> 6; // div 64
            int bit = index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] ^= bitmask;
            return (internalbits[wordNum] & bitmask) != 0;
        }
        
        /// <summary>flips a bit and returns the resulting bit value.
        /// The index should be less than the OpenBitSet size.
        /// </summary>
        public virtual bool FlipAndGet(long index)
        {
            int wordNum = (int) (index >> 6); // div 64
            int bit = (int) index & 0x3f; // mod 64
            long bitmask = 1L << bit;
            internalbits[wordNum] ^= bitmask;
            return (internalbits[wordNum] & bitmask) != 0;
        }
        
        /// <summary>Flips a range of bits, expanding the set size if necessary
        /// 
        /// </summary>
        /// <param name="startIndex">lower index
        /// </param>
        /// <param name="endIndex">one-past the last bit to flip
        /// </param>
        public virtual void  Flip(long startIndex, long endIndex)
        {
            if (endIndex <= startIndex)
                return ;
            int startWord = (int) (startIndex >> 6);
            
            // since endIndex is one past the end, this is index of the last
            // word to be changed.
            int endWord = ExpandingWordNum(endIndex - 1);
            
            /* Grrr, java shifting wraps around so -1L>>>64 == -1
            * for that reason, make sure not to use endmask if the bits to flip will
            * be zero in the last word (redefine endWord to be the last changed...)
            long startmask = -1L << (startIndex & 0x3f);     // example: 11111...111000
            long endmask = -1L >>> (64-(endIndex & 0x3f));   // example: 00111...111111
            ***/
            
            long startmask = - 1L << (int) startIndex;
            long endmask = (long) (0xffffffffffffffffUL >> (int) - endIndex); // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
            
            if (startWord == endWord)
            {
                internalbits[startWord] ^= (startmask & endmask);
                return ;
            }
            
            internalbits[startWord] ^= startmask;
            
            for (int i = startWord + 1; i < endWord; i++)
            {
                internalbits[i] = ~ internalbits[i];
            }
            
            internalbits[endWord] ^= endmask;
        }
        
        
        /*
        public static int pop(long v0, long v1, long v2, long v3) {
        // derived from pop_array by setting last four elems to 0.
        // exchanges one pop() call for 10 elementary operations
        // saving about 7 instructions... is there a better way?
        long twosA=v0 & v1;
        long ones=v0^v1;
        
        long u2=ones^v2;
        long twosB =(ones&v2)|(u2&v3);
        ones=u2^v3;
        
        long fours=(twosA&twosB);
        long twos=twosA^twosB;
        
        return (pop(fours)<<2)
        + (pop(twos)<<1)
        + pop(ones);
        
        }
        */
        
        
        /// <returns> the number of set bits 
        /// </returns>
        public virtual long Cardinality()
        {
            return BitUtil.Pop_array(internalbits, 0, wlen);
        }
        
        /// <summary>Returns the popcount or cardinality of the intersection of the two sets.
        /// Neither set is modified.
        /// </summary>
        public static long IntersectionCount(OpenBitSet a, OpenBitSet b)
        {
            return BitUtil.Pop_intersect(a.internalbits, b.internalbits, 0, System.Math.Min(a.wlen, b.wlen));
        }
        
        /// <summary>Returns the popcount or cardinality of the union of the two sets.
        /// Neither set is modified.
        /// </summary>
        public static long UnionCount(OpenBitSet a, OpenBitSet b)
        {
            long tot = BitUtil.Pop_union(a.internalbits, b.internalbits, 0, System.Math.Min(a.wlen, b.wlen));
            if (a.wlen < b.wlen)
            {
                tot += BitUtil.Pop_array(b.internalbits, a.wlen, b.wlen - a.wlen);
            }
            else if (a.wlen > b.wlen)
            {
                tot += BitUtil.Pop_array(a.internalbits, b.wlen, a.wlen - b.wlen);
            }
            return tot;
        }
        
        /// <summary>Returns the popcount or cardinality of "a and not b"
        /// or "intersection(a, not(b))".
        /// Neither set is modified.
        /// </summary>
        public static long AndNotCount(OpenBitSet a, OpenBitSet b)
        {
            long tot = BitUtil.Pop_andnot(a.internalbits, b.internalbits, 0, System.Math.Min(a.wlen, b.wlen));
            if (a.wlen > b.wlen)
            {
                tot += BitUtil.Pop_array(a.internalbits, b.wlen, a.wlen - b.wlen);
            }
            return tot;
        }
        
        /// <summary>Returns the popcount or cardinality of the exclusive-or of the two sets.
        /// Neither set is modified.
        /// </summary>
        public static long XorCount(OpenBitSet a, OpenBitSet b)
        {
            long tot = BitUtil.Pop_xor(a.internalbits, b.internalbits, 0, System.Math.Min(a.wlen, b.wlen));
            if (a.wlen < b.wlen)
            {
                tot += BitUtil.Pop_array(b.internalbits, a.wlen, b.wlen - a.wlen);
            }
            else if (a.wlen > b.wlen)
            {
                tot += BitUtil.Pop_array(a.internalbits, b.wlen, a.wlen - b.wlen);
            }
            return tot;
        }
        
        
        /// <summary>Returns the index of the first set bit starting at the index specified.
        /// -1 is returned if there are no more set bits.
        /// </summary>
        public virtual int NextSetBit(int index)
        {
            int i = index >> 6;
            if (i >= wlen)
                return - 1;
            int subIndex = index & 0x3f; // index within the word
            long word = internalbits[i] >> subIndex; // skip all the bits to the right of index
            
            if (word != 0)
            {
                return (i << 6) + subIndex + BitUtil.Ntz(word);
            }
            
            while (++i < wlen)
            {
                word = internalbits[i];
                if (word != 0)
                    return (i << 6) + BitUtil.Ntz(word);
            }
            
            return - 1;
        }
        
        /// <summary>Returns the index of the first set bit starting at the index specified.
        /// -1 is returned if there are no more set bits.
        /// </summary>
        public virtual long NextSetBit(long index)
        {
            int i = (int) (index >> 6);
            if (i >= wlen)
                return - 1;
            int subIndex = (int) index & 0x3f; // index within the word
            long word = (long) ((ulong) internalbits[i] >> subIndex); // skip all the bits to the right of index
            
            if (word != 0)
            {
                return (((long) i) << 6) + (subIndex + BitUtil.Ntz(word));
            }
            
            while (++i < wlen)
            {
                word = internalbits[i];
                if (word != 0)
                    return (((long) i) << 6) + BitUtil.Ntz(word);
            }
            
            return - 1;
        }
        
        
        
        
        public virtual System.Object Clone()
        {
            try
            {
                OpenBitSet obs = new OpenBitSet((long[]) internalbits.Clone(), wlen);
                //obs.bits = new long[obs.bits.Length];
                //obs.bits.CopyTo(obs.bits, 0); // hopefully an array clone is as fast(er) than arraycopy
                return obs;
            }
            catch (System.Exception e)
            {
                throw new System.SystemException(e.Message, e);
            }
        }
        
        /// <summary>this = this AND other </summary>
        public virtual void  Intersect(OpenBitSet other)
        {
            int newLen = System.Math.Min(this.wlen, other.wlen);
            long[] thisArr = this.internalbits;
            long[] otherArr = other.internalbits;
            // testing against zero can be more efficient
            int pos = newLen;
            while (--pos >= 0)
            {
                thisArr[pos] &= otherArr[pos];
            }
            if (this.wlen > newLen)
            {
                // fill zeros from the new shorter length to the old length
                for (int i = newLen; i < this.wlen; i++)
                    internalbits[i] = 0L;
            }
            this.wlen = newLen;
        }
        
        /// <summary>this = this OR other </summary>
        public virtual void  Union(OpenBitSet other)
        {
            int newLen = System.Math.Max(wlen, other.wlen);
            EnsureCapacityWords(newLen);
            
            long[] thisArr = this.internalbits;
            long[] otherArr = other.internalbits;
            int pos = System.Math.Min(wlen, other.wlen);
            while (--pos >= 0)
            {
                thisArr[pos] |= otherArr[pos];
            }
            if (this.wlen < newLen)
            {
                Array.Copy(otherArr, this.wlen, thisArr, this.wlen, newLen - this.wlen);
            }
            this.wlen = newLen;
        }
        
        
        /// <summary>Remove all elements set in other. this = this AND_NOT other </summary>
        public virtual void  Remove(OpenBitSet other)
        {
            int idx = System.Math.Min(wlen, other.wlen);
            long[] thisArr = this.internalbits;
            long[] otherArr = other.internalbits;
            while (--idx >= 0)
            {
                thisArr[idx] &= ~ otherArr[idx];
            }
        }
        
        /// <summary>this = this XOR other </summary>
        public virtual void  Xor(OpenBitSet other)
        {
            int newLen = System.Math.Max(wlen, other.wlen);
            EnsureCapacityWords(newLen);
            
            long[] thisArr = this.internalbits;
            long[] otherArr = other.internalbits;
            int pos = System.Math.Min(wlen, other.wlen);
            while (--pos >= 0)
            {
                thisArr[pos] ^= otherArr[pos];
            }
            if (this.wlen < newLen)
            {
                Array.Copy(otherArr, this.wlen, thisArr, this.wlen, newLen - this.wlen);
            }
            this.wlen = newLen;
        }
        
        
        // some BitSet compatability methods
        
        //* see <see cref="intersect" /> */
        public virtual void  And(OpenBitSet other)
        {
            Intersect(other);
        }
        
        //* see <see cref="union" /> */
        public virtual void  Or(OpenBitSet other)
        {
            Union(other);
        }
        
        //* see <see cref="andNot" /> */
        public virtual void  AndNot(OpenBitSet other)
        {
            Remove(other);
        }
        
        /// <summary>returns true if the sets have any elements in common </summary>
        public virtual bool Intersects(OpenBitSet other)
        {
            int pos = System.Math.Min(this.wlen, other.wlen);
            long[] thisArr = this.internalbits;
            long[] otherArr = other.internalbits;
            while (--pos >= 0)
            {
                if ((thisArr[pos] & otherArr[pos]) != 0)
                    return true;
            }
            return false;
        }
        
        
        
        /// <summary>Expand the long[] with the size given as a number of words (64 bit longs).
        /// getNumWords() is unchanged by this call.
        /// </summary>
        public virtual void  EnsureCapacityWords(int numWords)
        {
            if (internalbits.Length < numWords)
            {
                internalbits = ArrayUtil.Grow(internalbits, numWords);
            }
        }
        
        /// <summary>Ensure that the long[] is big enough to hold numBits, expanding it if necessary.
        /// getNumWords() is unchanged by this call.
        /// </summary>
        public virtual void  EnsureCapacity(long numBits)
        {
            EnsureCapacityWords(Bits2words(numBits));
        }
        
        /// <summary>Lowers numWords, the number of words in use,
        /// by checking for trailing zero words.
        /// </summary>
        public virtual void  TrimTrailingZeros()
        {
            int idx = wlen - 1;
            while (idx >= 0 && internalbits[idx] == 0)
                idx--;
            wlen = idx + 1;
        }
        
        /// <summary>returns the number of 64 bit words it would take to hold numBits </summary>
        public static int Bits2words(long numBits)
        {
            return (int) ((((numBits - 1) >> 6)) + 1);
        }
        
        
        /// <summary>returns true if both sets have the same bits set </summary>
        public override bool Equals(System.Object o)
        {
            if (this == o)
                return true;
            if (!(o is OpenBitSet))
                return false;
            OpenBitSet a;
            OpenBitSet b = (OpenBitSet) o;
            // make a the larger set.
            if (b.wlen > this.wlen)
            {
                a = b; b = this;
            }
            else
            {
                a = this;
            }
            
            // check for any set bits out of the range of b
            for (int i = a.wlen - 1; i >= b.wlen; i--)
            {
                if (a.internalbits[i] != 0)
                    return false;
            }
            
            for (int i = b.wlen - 1; i >= 0; i--)
            {
                if (a.internalbits[i] != b.internalbits[i])
                    return false;
            }
            
            return true;
        }

        public override int GetHashCode()
        {
            // Start with a zero hash and use a mix that results in zero if the input is zero.
            // This effectively truncates trailing zeros without an explicit check.
            long h = 0;
            for (int i = internalbits.Length; --i >= 0; )
            {
                h ^= internalbits[i];
                h = (h << 1) | (Number.URShift(h, 63)); // rotate left
            }
            // fold leftmost bits into right and add a constant to prevent
            // empty sets from returning 0, which is too common.
            return (int)(((h >> 32) ^ h) + 0x98761234);
        }

        
    }
}