content: /*
   * 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
   * limitations under the License.
   */
  
  package org.apache.spark.unsafe.bitset;
  
  import org.apache.spark.unsafe.Platform;
  
  /**
   * Methods for working with fixed-size uncompressed bitsets.
   *
   * We assume that the bitset data is word-aligned (that is, a multiple of 8 bytes in length).
   *
   * Each bit occupies exactly one bit of storage.
   */
  public final class BitSetMethods {
  
    private static final long WORD_SIZE = 8;
  
    private BitSetMethods() {
      // Make the default constructor private, since this only holds static methods.
    }
  
    /**
     * Sets the bit at the specified index to {@code true}.
     */
    public static void set(Object baseObject, long baseOffset, int index) {
      assert index >= 0 : "index (" + index + ") should >= 0";
      final long mask = 1L << (index & 0x3f);  // mod 64 and shift
      final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
      final long word = Platform.getLong(baseObject, wordOffset);
      Platform.putLong(baseObject, wordOffset, word | mask);
    }
  
    /**
     * Sets the bit at the specified index to {@code false}.
     */
    public static void unset(Object baseObject, long baseOffset, int index) {
      assert index >= 0 : "index (" + index + ") should >= 0";
      final long mask = 1L << (index & 0x3f);  // mod 64 and shift
      final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
      final long word = Platform.getLong(baseObject, wordOffset);
      Platform.putLong(baseObject, wordOffset, word & ~mask);
    }
  
    /**
     * Returns {@code true} if the bit is set at the specified index.
     */
    public static boolean isSet(Object baseObject, long baseOffset, int index) {
      assert index >= 0 : "index (" + index + ") should >= 0";
      final long mask = 1L << (index & 0x3f);  // mod 64 and shift
      final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
      final long word = Platform.getLong(baseObject, wordOffset);
      return (word & mask) != 0;
    }
  
    /**
     * Returns {@code true} if any bit is set.
     */
    public static boolean anySet(Object baseObject, long baseOffset, long bitSetWidthInWords) {
      long addr = baseOffset;
      for (int i = 0; i < bitSetWidthInWords; i++, addr += WORD_SIZE) {
        if (Platform.getLong(baseObject, addr) != 0) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * Returns the index of the first bit that is set to true that occurs on or after the
     * specified starting index. If no such bit exists then {@code -1} is returned.
     * <p>
     * To iterate over the true bits in a BitSet, use the following loop:
     * <pre>
     * <code>
     *  for (long i = bs.nextSetBit(0, sizeInWords); i &gt;= 0;
     *    i = bs.nextSetBit(i + 1, sizeInWords)) {
     *    // operate on index i here
     *  }
     * </code>
     * </pre>
     *
     * @param fromIndex the index to start checking from (inclusive)
     * @param bitsetSizeInWords the size of the bitset, measured in 8-byte words
     * @return the index of the next set bit, or -1 if there is no such bit
     */
    public static int nextSetBit(
        Object baseObject,
        long baseOffset,
        int fromIndex,
        int bitsetSizeInWords) {
      int wi = fromIndex >> 6;
      if (wi >= bitsetSizeInWords) {
        return -1;
      }
  
      // Try to find the next set bit in the current word
      final int subIndex = fromIndex & 0x3f;
      long word = Platform.getLong(baseObject, baseOffset + wi * WORD_SIZE) >> subIndex;
      if (word != 0) {
        return (wi << 6) + subIndex + java.lang.Long.numberOfTrailingZeros(word);
      }
  
      // Find the next set bit in the rest of the words
      wi += 1;
      while (wi < bitsetSizeInWords) {
        word = Platform.getLong(baseObject, baseOffset + wi * WORD_SIZE);
        if (word != 0) {
          return (wi << 6) + java.lang.Long.numberOfTrailingZeros(word);
        }
        wi += 1;
      }
  
      return -1;
    }
  }
  