content: package net.agkn.hll.util;
  
  /*
   * Copyright 2013 Aggregate Knowledge, Inc.
   *
   * Licensed 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.
   */
  
  /**
   * A collection of bit utilities.
   *
   * @author rgrzywinski
   */
  public class BitUtil {
      /**
       * The set of least-significant bits for a given <code>byte</code>.  <code>-1</code>
       * is used if no bits are set (so as to not be confused with "index of zero"
       * meaning that the least significant bit is the 0th (1st) bit).
       *
       * @see #leastSignificantBit(long)
       */
      private static final int[] LEAST_SIGNIFICANT_BIT = {
         -1, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
          4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
      };
  
      /**
       * Computes the least-significant bit of the specified <code>long</code>
       * that is set to <code>1</code>. Zero-indexed.
       *
       * @param  value the <code>long</code> whose least-significant bit is desired.
       * @return the least-significant bit of the specified <code>long</code>.
       *         <code>-1</code> is returned if there are no bits set.
       */
      // REF:  http://stackoverflow.com/questions/757059/position-of-least-significant-bit-that-is-set
      // REF:  http://www-graphics.stanford.edu/~seander/bithacks.html
      public static int leastSignificantBit(final long value) {
          if(value == 0L) return -1/*by contract*/;
          if((value & 0xFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>>  0) & 0xFF)] +  0;
          if((value & 0xFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>>  8) & 0xFF)] +  8;
          if((value & 0xFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 16) & 0xFF)] + 16;
          if((value & 0xFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 24) & 0xFF)] + 24;
          if((value & 0xFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 32) & 0xFF)] + 32;
          if((value & 0xFFFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 40) & 0xFF)] + 40;
          if((value & 0xFFFFFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 48) & 0xFF)] + 48;
          return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 56) & 0xFFL)] + 56;
      }
  }