SparseFixedBitSet#firstDoc: reduce number of `indices` iterations for a bit set that is not fully built yet. (#13559)

lucene/CHANGES.txt

@@ -108,8 +108,11 @@ API Changes
 
 * GITHUB#13410: Removed Scorer#getWeight (Sanjay Dutt, Adrien Grand)
 
+* GITHUB#13559: Add BitSet#nextSetBit(int, int) to get the index of the first set bit in range. (Egor Potemkin)
+
 * GITHUB#13499: Remove deprecated TopScoreDocCollector + TopFieldCollector methods (#create, #createSharedManager) (Jakub Slowinski)
 
+
 New Features
 ---------------------
 

lucene/core/src/java/org/apache/lucene/util/BitSet.java

@@ -92,6 +92,12 @@ public abstract class BitSet implements Bits, Accountable {
    */
   public abstract int nextSetBit(int index);
 
+  /**
+   * Returns the index of the first set bit from start (inclusive) until end (exclusive). {@link
+   * DocIdSetIterator#NO_MORE_DOCS} is returned if there are no more set bits.
+   */
+  public abstract int nextSetBit(int start, int end);
+
   /** Assert that the current doc is -1. */
   protected final void checkUnpositioned(DocIdSetIterator iter) {
     if (iter.docID() != -1) {

lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java

@@ -291,6 +291,32 @@ public final class FixedBitSet extends BitSet {
     return DocIdSetIterator.NO_MORE_DOCS;
   }
 
+  @Override
+  public int nextSetBit(int start, int upperBound) {
+    // Depends on the ghost bits being clear!
+    assert start >= 0 && start < numBits : "index=" + start + ", numBits=" + numBits;
+    assert start < upperBound : "index=" + start + ", upperBound=" + upperBound;
+    assert upperBound <= numBits : "upperBound=" + upperBound + ", numBits=" + numBits;
+    int i = start >> 6;
+    long word = bits[i] >> start; // skip all the bits to the right of index
+
+    if (word != 0) {
+      int res = start + Long.numberOfTrailingZeros(word);
+      return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+    }
+
+    int limit = bits2words(upperBound);
+    while (++i < limit) {
+      word = bits[i];
+      if (word != 0) {
+        int res = (i << 6) + Long.numberOfTrailingZeros(word);
+        return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+      }
+    }
+
+    return DocIdSetIterator.NO_MORE_DOCS;
+  }
+
   @Override
   public int prevSetBit(int index) {
     assert index >= 0 && index < numBits : "index=" + index + " numBits=" + numBits;

lucene/core/src/java/org/apache/lucene/util/SparseFixedBitSet.java

@@ -320,9 +320,11 @@ public class SparseFixedBitSet extends BitSet {
   }
 
   /** Return the first document that occurs on or after the provided block index. */
-  private int firstDoc(int i4096) {
+  private int firstDoc(int i4096, int i4096upper) {
+    assert i4096upper <= indices.length
+        : "i4096upper=" + i4096 + ", indices.length=" + indices.length;
     long index = 0;
-    while (i4096 < indices.length) {
+    while (i4096 < i4096upper) {
       index = indices[i4096];
       if (index != 0) {
         final int i64 = Long.numberOfTrailingZeros(index);
@@ -353,7 +355,7 @@ public class SparseFixedBitSet extends BitSet {
     final long indexBits = index >>> i64 >>> 1;
     if (indexBits == 0) {
       // no more bits are set in the current block of 4096 bits, go to the next one
-      return firstDoc(i4096 + 1);
+      return firstDoc(i4096 + 1, indices.length);
     }
     // there are still set bits
     i64 += 1 + Long.numberOfTrailingZeros(indexBits);
@@ -361,6 +363,39 @@ public class SparseFixedBitSet extends BitSet {
     return (i64 << 6) | Long.numberOfTrailingZeros(bits);
   }
 
+  @Override
+  public int nextSetBit(int start, int upperBound) {
+    assert start < length;
+    assert upperBound > start;
+    final int i4096 = start >>> 12;
+    final long index = indices[i4096];
+    final long[] bitArray = this.bits[i4096];
+    int i64 = start >>> 6;
+    final long i64bit = 1L << i64;
+    int o = Long.bitCount(index & (i64bit - 1));
+    if ((index & i64bit) != 0) {
+      // There is at least one bit that is set in the current long, check if
+      // one of them is after i
+      final long bits = bitArray[o] >>> start; // shifts are mod 64
+      if (bits != 0) {
+        int res = start + Long.numberOfTrailingZeros(bits);
+        return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+      }
+      o += 1;
+    }
+    final long indexBits = index >>> i64 >>> 1;
+    if (indexBits == 0) {
+      // no more bits are set in the current block of 4096 bits, go to the next one
+      int res = firstDoc(i4096 + 1, blockCount(upperBound));
+      return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+    }
+    // there are still set bits
+    i64 += 1 + Long.numberOfTrailingZeros(indexBits);
+    final long bits = bitArray[o];
+    int res = (i64 << 6) | Long.numberOfTrailingZeros(bits);
+    return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+  }
+
   /** Return the last document that occurs on or before the provided block index. */
   private int lastDoc(int i4096) {
     long index;

lucene/join/src/java/org/apache/lucene/search/join/BlockJoinSelector.java

@@ -64,14 +64,20 @@ public class BlockJoinSelector {
           return false;
         }
 
-        final int firstChild = parents.prevSetBit(docID - 1) + 1;
-        for (int child = children.nextSetBit(firstChild);
-            child < docID;
-            child = children.nextSetBit(child + 1)) {
+        final int firstPotentialChild = parents.prevSetBit(docID - 1) + 1;
+        assert firstPotentialChild <= docID;
+        if (firstPotentialChild == docID) {
+          // no children
+          return false;
+        }
+        for (int child = children.nextSetBit(firstPotentialChild, docID);
+            child != DocIdSetIterator.NO_MORE_DOCS;
+            child = children.nextSetBit(child + 1, docID)) {
           if (docsWithValue.get(child)) {
             return true;
           }
         }
+
         return false;
       }
 

lucene/test-framework/src/java/org/apache/lucene/tests/util/BaseBitSetTestCase.java

@@ -16,6 +16,7 @@
  */
 package org.apache.lucene.tests.util;
 
+import com.carrotsearch.randomizedtesting.generators.RandomNumbers;
 import java.io.IOException;
 import java.util.Collection;
 import java.util.Collections;
@@ -104,6 +105,23 @@ public abstract class BaseBitSetTestCase<T extends BitSet> extends LuceneTestCas
     }
   }
 
+  /** Test {@link BitSet#nextSetBit(int, int)}. */
+  public void testNextSetBitInRange() throws IOException {
+    Random random = random();
+    final int numBits = 1 + random().nextInt(100000);
+    for (float percentSet : new float[] {0, 0.01f, 0.1f, 0.5f, 0.9f, 0.99f, 1f}) {
+      BitSet set1 = new JavaUtilBitSet(randomSet(numBits, percentSet), numBits);
+      T set2 = copyOf(set1, numBits);
+      for (int start = 0; start < numBits; ++start) {
+        int end = RandomNumbers.randomIntBetween(random, start + 1, numBits);
+        assertEquals(
+            "start=" + start + ", end=" + end + ", numBits=" + numBits,
+            set1.nextSetBit(start, end),
+            set2.nextSetBit(start, end));
+      }
+    }
+  }
+
   /** Test the {@link BitSet#set} method. */
   public void testSet() throws IOException {
     Random random = random();
@@ -330,5 +348,11 @@ public abstract class BaseBitSetTestCase<T extends BitSet> extends LuceneTestCas
       }
       return next;
     }
+
+    @Override
+    public int nextSetBit(int start, int upperBound) {
+      int res = nextSetBit(start);
+      return res < upperBound ? res : DocIdSetIterator.NO_MORE_DOCS;
+    }
   }
 }