org.roaringbitmap.BitmapBatchIterator Maven / Gradle / Ivy

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Roaring bitmaps are compressed bitmaps (also called bitsets) which tend to outperform conventional compressed bitmaps such as WAH or Concise.

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package org.roaringbitmap;

import static java.lang.Long.numberOfTrailingZeros;

public final class BitmapBatchIterator implements ContainerBatchIterator {

  private int wordIndex = 0;
  private long word;
  private BitmapContainer bitmap;

  public BitmapBatchIterator(BitmapContainer bitmap) {
    wrap(bitmap);
  }

  @Override
  public int next(int key, int[] buffer, int offset) {
    int consumed = 0;
    while ((consumed + offset) < buffer.length) {
      while (word == 0) {
        ++wordIndex;
        if (wordIndex == 1024) {
          return consumed;
        }
        word = bitmap.bitmap[wordIndex];
      }
      buffer[offset + consumed++] = key + (64 * wordIndex) + numberOfTrailingZeros(word);
      word &= (word - 1);
    }
    return consumed;
  }

  @Override
  public boolean hasNext() {
    if (wordIndex > 1023) {
      return false;
    }
    while (word == 0) {
      ++wordIndex;
      if (wordIndex == 1024) { // reached end without a non-empty word
        return false;
      }
      word = bitmap.bitmap[wordIndex];
    }
    return true; // found some non-empty word, so hasNext
  }

  @Override
  public ContainerBatchIterator clone() {
    try {
      return (ContainerBatchIterator)super.clone();
    } catch (CloneNotSupportedException e) {
      // won't happen
      throw new IllegalStateException(e);
    }
  }

  @Override
  public void releaseContainer() {
    bitmap = null;
  }

  @Override
  public void advanceIfNeeded(char target) {
    wordIndex = target >>> 6;
    word = bitmap.bitmap[wordIndex];
    word &= -(1L << target);
  }

  void wrap(BitmapContainer bitmap) {
    this.bitmap = bitmap;
    word = bitmap.bitmap[0];
    this.wordIndex = 0;
  }
}