/*
 * 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.lucene.util; // from org.apache.solr.util rev 555343

/**  A variety of high efficiency bit twiddling routines.
 * @lucene.internal
 */
public final class BitUtil {

  private static final byte[] BYTE_COUNTS = {  // table of bits/byte
    0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
    1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
    1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
    1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
    2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
    3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
    3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
    4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
  };

  // The General Idea: instead of having an array per byte that has
  // the offsets of the next set bit, that array could be
  // packed inside a 32 bit integer (8 4 bit numbers).  That
  // should be faster than accessing an array for each index, and
  // the total array size is kept smaller (256*sizeof(int))=1K
  /***** the python code that generated bitlist
  def bits2int(val):
  arr=0
  for shift in range(8,0,-1):
    if val & 0x80:
      arr = (arr << 4) | shift
    val = val << 1
  return arr

  def int_table():
    tbl = [ hex(bits2int(val)).strip('L') for val in range(256) ]
    return ','.join(tbl)
  ******/
  private static final int[] BIT_LISTS = {
    0x0, 0x1, 0x2, 0x21, 0x3, 0x31, 0x32, 0x321, 0x4, 0x41, 0x42, 0x421, 0x43, 
    0x431, 0x432, 0x4321, 0x5, 0x51, 0x52, 0x521, 0x53, 0x531, 0x532, 0x5321, 
    0x54, 0x541, 0x542, 0x5421, 0x543, 0x5431, 0x5432, 0x54321, 0x6, 0x61, 0x62, 
    0x621, 0x63, 0x631, 0x632, 0x6321, 0x64, 0x641, 0x642, 0x6421, 0x643, 
    0x6431, 0x6432, 0x64321, 0x65, 0x651, 0x652, 0x6521, 0x653, 0x6531, 0x6532, 
    0x65321, 0x654, 0x6541, 0x6542, 0x65421, 0x6543, 0x65431, 0x65432, 0x654321, 
    0x7, 0x71, 0x72, 0x721, 0x73, 0x731, 0x732, 0x7321, 0x74, 0x741, 0x742,
    0x7421, 0x743, 0x7431, 0x7432, 0x74321, 0x75, 0x751, 0x752, 0x7521, 0x753, 
    0x7531, 0x7532, 0x75321, 0x754, 0x7541, 0x7542, 0x75421, 0x7543, 0x75431, 
    0x75432, 0x754321, 0x76, 0x761, 0x762, 0x7621, 0x763, 0x7631, 0x7632, 
    0x76321, 0x764, 0x7641, 0x7642, 0x76421, 0x7643, 0x76431, 0x76432, 0x764321, 
    0x765, 0x7651, 0x7652, 0x76521, 0x7653, 0x76531, 0x76532, 0x765321, 0x7654, 
    0x76541, 0x76542, 0x765421, 0x76543, 0x765431, 0x765432, 0x7654321, 0x8, 
    0x81, 0x82, 0x821, 0x83, 0x831, 0x832, 0x8321, 0x84, 0x841, 0x842, 0x8421, 
    0x843, 0x8431, 0x8432, 0x84321, 0x85, 0x851, 0x852, 0x8521, 0x853, 0x8531, 
    0x8532, 0x85321, 0x854, 0x8541, 0x8542, 0x85421, 0x8543, 0x85431, 0x85432, 
    0x854321, 0x86, 0x861, 0x862, 0x8621, 0x863, 0x8631, 0x8632, 0x86321, 0x864, 
    0x8641, 0x8642, 0x86421, 0x8643, 0x86431, 0x86432, 0x864321, 0x865, 0x8651, 
    0x8652, 0x86521, 0x8653, 0x86531, 0x86532, 0x865321, 0x8654, 0x86541, 
    0x86542, 0x865421, 0x86543, 0x865431, 0x865432, 0x8654321, 0x87, 0x871, 
    0x872, 0x8721, 0x873, 0x8731, 0x8732, 0x87321, 0x874, 0x8741, 0x8742, 
    0x87421, 0x8743, 0x87431, 0x87432, 0x874321, 0x875, 0x8751, 0x8752, 0x87521, 
    0x8753, 0x87531, 0x87532, 0x875321, 0x8754, 0x87541, 0x87542, 0x875421, 
    0x87543, 0x875431, 0x875432, 0x8754321, 0x876, 0x8761, 0x8762, 0x87621, 
    0x8763, 0x87631, 0x87632, 0x876321, 0x8764, 0x87641, 0x87642, 0x876421, 
    0x87643, 0x876431, 0x876432, 0x8764321, 0x8765, 0x87651, 0x87652, 0x876521, 
    0x87653, 0x876531, 0x876532, 0x8765321, 0x87654, 0x876541, 0x876542, 
    0x8765421, 0x876543, 0x8765431, 0x8765432, 0x87654321
  };

  private BitUtil() {} // no instance

  /** Return the number of bits sets in b. */
  public static int bitCount(byte b) {
    return BYTE_COUNTS[b & 0xFF];
  }

  /** Return the list of bits which are set in b encoded as followed:
   * <code>(i >>> (4 * n)) & 0x0F</code> is the offset of the n-th set bit of
   * the given byte plus one, or 0 if there are n or less bits set in the given
   * byte. For example <code>bitList(12)</code> returns 0x43:<ul>
   * <li><code>0x43 & 0x0F</code> is 3, meaning the the first bit set is at offset 3-1 = 2,</li>
   * <li><code>(0x43 >>> 4) & 0x0F</code> is 4, meaning there is a second bit set at offset 4-1=3,</li>
   * <li><code>(0x43 >>> 8) & 0x0F</code> is 0, meaning there is no more bit set in this byte.</li>
   * </ul>*/
  public static int bitList(byte b) {
    return BIT_LISTS[b & 0xFF];
  }

  // The pop methods used to rely on bit-manipulation tricks for speed but it
  // turns out that it is faster to use the Long.bitCount method (which is an
  // intrinsic since Java 6u18) in a naive loop, see LUCENE-2221

  /** Returns the number of set bits in an array of longs. */
  public static long pop_array(long[] arr, int wordOffset, int numWords) {
    long popCount = 0;
    for (int i = wordOffset, end = wordOffset + numWords; i < end; ++i) {
      popCount += Long.bitCount(arr[i]);
    }
    return popCount;
  }

  /** Returns the popcount or cardinality of the two sets after an intersection.
   *  Neither array is modified. */
  public static long pop_intersect(long[] arr1, long[] arr2, int wordOffset, int numWords) {
    long popCount = 0;
    for (int i = wordOffset, end = wordOffset + numWords; i < end; ++i) {
      popCount += Long.bitCount(arr1[i] & arr2[i]);
    }
    return popCount;
  }

   /** Returns the popcount or cardinality of the union of two sets.
    *  Neither array is modified. */
   public static long pop_union(long[] arr1, long[] arr2, int wordOffset, int numWords) {
     long popCount = 0;
     for (int i = wordOffset, end = wordOffset + numWords; i < end; ++i) {
       popCount += Long.bitCount(arr1[i] | arr2[i]);
     }
     return popCount;
   }

  /** Returns the popcount or cardinality of A & ~B.
   *  Neither array is modified. */
  public static long pop_andnot(long[] arr1, long[] arr2, int wordOffset, int numWords) {
    long popCount = 0;
    for (int i = wordOffset, end = wordOffset + numWords; i < end; ++i) {
      popCount += Long.bitCount(arr1[i] & ~arr2[i]);
    }
    return popCount;
  }

  /** Returns the popcount or cardinality of A ^ B
    * Neither array is modified. */
  public static long pop_xor(long[] arr1, long[] arr2, int wordOffset, int numWords) {
    long popCount = 0;
    for (int i = wordOffset, end = wordOffset + numWords; i < end; ++i) {
      popCount += Long.bitCount(arr1[i] ^ arr2[i]);
    }
    return popCount;
  }

  /** returns the next highest power of two, or the current value if it's already a power of two or zero*/
  public static int nextHighestPowerOfTwo(int v) {
    v--;
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    v++;
    return v;
  }

  /** returns the next highest power of two, or the current value if it's already a power of two or zero*/
   public static long nextHighestPowerOfTwo(long v) {
    v--;
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    v |= v >> 32;
    v++;
    return v;
  }

}
