Source Code Cross Referenced for BitSetIterator.java in  » Search-Engine » apache-solr-1.2.0 » org » apache » solr » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Search Engine » apache solr 1.2.0 » org.apache.solr.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /**
002:         * Licensed to the Apache Software Foundation (ASF) under one or more
003:         * contributor license agreements.  See the NOTICE file distributed with
004:         * this work for additional information regarding copyright ownership.
005:         * The ASF licenses this file to You under the Apache License, Version 2.0
006:         * (the "License"); you may not use this file except in compliance with
007:         * the License.  You may obtain a copy of the License at
008:         *
009:         *     http://www.apache.org/licenses/LICENSE-2.0
010:         *
011:         * Unless required by applicable law or agreed to in writing, software
012:         * distributed under the License is distributed on an "AS IS" BASIS,
013:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014:         * See the License for the specific language governing permissions and
015:         * limitations under the License.
016:         */package org.apache.solr.util;
017:
018:        /** An iterator to iterate over set bits in an OpenBitSet.
019:         * This is faster than nextSetBit() for iterating over the complete set of bits,
020:         * especially when the density of the bits set is high.
021:         *
022:         * @author yonik
023:         * @version $Id$
024:         */
025:        public class BitSetIterator {
026:
027:            // The General Idea: instead of having an array per byte that has
028:            // the offsets of the next set bit, that array could be
029:            // packed inside a 32 bit integer (8 4 bit numbers).  That
030:            // should be faster than accessing an array for each index, and
031:            // the total array size is kept smaller (256*sizeof(int))=1K
032:            protected final static int[] bitlist = { 0x0, 0x1, 0x2, 0x21, 0x3,
033:                    0x31, 0x32, 0x321, 0x4, 0x41, 0x42, 0x421, 0x43, 0x431,
034:                    0x432, 0x4321, 0x5, 0x51, 0x52, 0x521, 0x53, 0x531, 0x532,
035:                    0x5321, 0x54, 0x541, 0x542, 0x5421, 0x543, 0x5431, 0x5432,
036:                    0x54321, 0x6, 0x61, 0x62, 0x621, 0x63, 0x631, 0x632,
037:                    0x6321, 0x64, 0x641, 0x642, 0x6421, 0x643, 0x6431, 0x6432,
038:                    0x64321, 0x65, 0x651, 0x652, 0x6521, 0x653, 0x6531, 0x6532,
039:                    0x65321, 0x654, 0x6541, 0x6542, 0x65421, 0x6543, 0x65431,
040:                    0x65432, 0x654321, 0x7, 0x71, 0x72, 0x721, 0x73, 0x731,
041:                    0x732, 0x7321, 0x74, 0x741, 0x742, 0x7421, 0x743, 0x7431,
042:                    0x7432, 0x74321, 0x75, 0x751, 0x752, 0x7521, 0x753, 0x7531,
043:                    0x7532, 0x75321, 0x754, 0x7541, 0x7542, 0x75421, 0x7543,
044:                    0x75431, 0x75432, 0x754321, 0x76, 0x761, 0x762, 0x7621,
045:                    0x763, 0x7631, 0x7632, 0x76321, 0x764, 0x7641, 0x7642,
046:                    0x76421, 0x7643, 0x76431, 0x76432, 0x764321, 0x765, 0x7651,
047:                    0x7652, 0x76521, 0x7653, 0x76531, 0x76532, 0x765321,
048:                    0x7654, 0x76541, 0x76542, 0x765421, 0x76543, 0x765431,
049:                    0x765432, 0x7654321, 0x8, 0x81, 0x82, 0x821, 0x83, 0x831,
050:                    0x832, 0x8321, 0x84, 0x841, 0x842, 0x8421, 0x843, 0x8431,
051:                    0x8432, 0x84321, 0x85, 0x851, 0x852, 0x8521, 0x853, 0x8531,
052:                    0x8532, 0x85321, 0x854, 0x8541, 0x8542, 0x85421, 0x8543,
053:                    0x85431, 0x85432, 0x854321, 0x86, 0x861, 0x862, 0x8621,
054:                    0x863, 0x8631, 0x8632, 0x86321, 0x864, 0x8641, 0x8642,
055:                    0x86421, 0x8643, 0x86431, 0x86432, 0x864321, 0x865, 0x8651,
056:                    0x8652, 0x86521, 0x8653, 0x86531, 0x86532, 0x865321,
057:                    0x8654, 0x86541, 0x86542, 0x865421, 0x86543, 0x865431,
058:                    0x865432, 0x8654321, 0x87, 0x871, 0x872, 0x8721, 0x873,
059:                    0x8731, 0x8732, 0x87321, 0x874, 0x8741, 0x8742, 0x87421,
060:                    0x8743, 0x87431, 0x87432, 0x874321, 0x875, 0x8751, 0x8752,
061:                    0x87521, 0x8753, 0x87531, 0x87532, 0x875321, 0x8754,
062:                    0x87541, 0x87542, 0x875421, 0x87543, 0x875431, 0x875432,
063:                    0x8754321, 0x876, 0x8761, 0x8762, 0x87621, 0x8763, 0x87631,
064:                    0x87632, 0x876321, 0x8764, 0x87641, 0x87642, 0x876421,
065:                    0x87643, 0x876431, 0x876432, 0x8764321, 0x8765, 0x87651,
066:                    0x87652, 0x876521, 0x87653, 0x876531, 0x876532, 0x8765321,
067:                    0x87654, 0x876541, 0x876542, 0x8765421, 0x876543,
068:                    0x8765431, 0x8765432, 0x87654321 };
069:            /***** the python code that generated bitlist
070:            def bits2int(val):
071:            arr=0
072:            for shift in range(8,0,-1):
073:              if val & 0x80:
074:                arr = (arr << 4) | shift
075:              val = val << 1
076:            return arr
077:
078:            def int_table():
079:              tbl = [ hex(bits2int(val)).strip('L') for val in range(256) ]
080:              return ','.join(tbl)
081:             ******/
082:
083:            // hmmm, what about an iterator that finds zeros though,
084:            // or a reverse iterator... should they be separate classes
085:            // for efficiency, or have a common root interface?  (or
086:            // maybe both?  could ask for a SetBitsIterator, etc...
087:
088:            private final long[] arr;
089:            private final int words;
090:            private int i = -1;
091:            private long word;
092:            private int wordShift;
093:            private int indexArray;
094:
095:            public BitSetIterator(OpenBitSet obs) {
096:                this (obs.getBits(), obs.getNumWords());
097:            }
098:
099:            public BitSetIterator(long[] bits, int numWords) {
100:                arr = bits;
101:                words = numWords;
102:            }
103:
104:            // 64 bit shifts
105:            private void shift() {
106:                if ((int) word == 0) {
107:                    wordShift += 32;
108:                    word = word >>> 32;
109:                }
110:                if ((word & 0x0000FFFF) == 0) {
111:                    wordShift += 16;
112:                    word >>>= 16;
113:                }
114:                if ((word & 0x000000FF) == 0) {
115:                    wordShift += 8;
116:                    word >>>= 8;
117:                }
118:                indexArray = bitlist[(int) word & 0xff];
119:            }
120:
121:            /***** alternate shift implementations
122:            // 32 bit shifts, but a long shift needed at the end
123:            private void shift2() {
124:              int y = (int)word;
125:              if (y==0) {wordShift +=32; y = (int)(word >>>32); }
126:              if ((y & 0x0000FFFF) == 0) { wordShift +=16; y>>>=16; }
127:              if ((y & 0x000000FF) == 0) { wordShift +=8; y>>>=8; }
128:              indexArray = bitlist[y & 0xff];
129:              word >>>= (wordShift +1);
130:            }
131:
132:            private void shift3() {
133:              int lower = (int)word;
134:              int lowByte = lower & 0xff;
135:              if (lowByte != 0) {
136:                indexArray=bitlist[lowByte];
137:                return;
138:              }
139:              shift();
140:            }
141:             ******/
142:
143:            public int next() {
144:                if (indexArray == 0) {
145:                    if (word != 0) {
146:                        word >>>= 8;
147:                        wordShift += 8;
148:                    }
149:
150:                    while (word == 0) {
151:                        if (++i >= words)
152:                            return -1;
153:                        word = arr[i];
154:                        wordShift = -1; // loop invariant code motion should move this
155:                    }
156:
157:                    // after the first time, should I go with a linear search, or
158:                    // stick with the binary search in shift?
159:                    shift();
160:                }
161:
162:                int bitIndex = (indexArray & 0x0f) + wordShift;
163:                indexArray >>>= 4;
164:                // should i<<6 be cached as a separate variable?
165:                // it would only save one cycle in the best circumstances.
166:                return (i << 6) + bitIndex;
167:            }
168:
169:            public int next(int fromIndex) {
170:                indexArray = 0;
171:                i = fromIndex >> 6;
172:                if (i >= words) {
173:                    word = 0; // setup so next() will also return -1
174:                    return -1;
175:                }
176:                wordShift = fromIndex & 0x3f;
177:                word = arr[i] >>> wordShift;
178:                if (word != 0) {
179:                    wordShift--; // compensate for 1 based arrIndex
180:                } else {
181:                    while (word == 0) {
182:                        if (++i >= words)
183:                            return -1;
184:                        word = arr[i];
185:                    }
186:                    wordShift = -1;
187:                }
188:
189:                shift();
190:
191:                int bitIndex = (indexArray & 0x0f) + wordShift;
192:                indexArray >>>= 4;
193:                // should i<<6 be cached as a separate variable?
194:                // it would only save one cycle in the best circumstances.
195:                return (i << 6) + bitIndex;
196:            }
197:
198:        }
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