content: package org.apache.lucene.util.packed;
  
  /**
   * 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.
   */
  
  import org.apache.lucene.store.DataInput;
  import org.apache.lucene.util.RamUsageEstimator;
  
  import java.io.IOException;
  import java.util.Arrays;
  
  /**
   * Space optimized random access capable array of values with a fixed number of
   * bits. The maximum number of bits/value is 31. Use {@link Packed64} for higher
   * numbers.
   * </p><p>
   * The implementation strives to avoid conditionals and expensive operations,
   * sacrificing code clarity to achieve better performance.
   */
  
  class Packed32 extends PackedInts.ReaderImpl implements PackedInts.Mutable {
    static final int BLOCK_SIZE = 32; // 32 = int, 64 = long
    static final int BLOCK_BITS = 5; // The #bits representing BLOCK_SIZE
    static final int MOD_MASK = BLOCK_SIZE - 1; // x % BLOCK_SIZE
  
    private static final int ENTRY_SIZE = BLOCK_SIZE + 1;
    private static final int FAC_BITPOS = 3;
  
    /*
     * In order to make an efficient value-getter, conditionals should be
     * avoided. A value can be positioned inside of a block, requiring shifting
     * left or right or it can span two blocks, requiring a left-shift on the
     * first block and a right-shift on the right block.
     * </p><p>
     * By always shifting the first block both left and right, we get exactly
     * the right bits. By always shifting the second block right and applying
     * a mask, we get the right bits there. After that, we | the two bitsets.
    */
    private static final int[][] SHIFTS =
            new int[ENTRY_SIZE][ENTRY_SIZE * FAC_BITPOS];
    private static final int[][] MASKS = new int[ENTRY_SIZE][ENTRY_SIZE];
  
    static { // Generate shifts
      for (int elementBits = 1 ; elementBits <= BLOCK_SIZE ; elementBits++) {
        for (int bitPos = 0 ; bitPos < BLOCK_SIZE ; bitPos++) {
          int[] currentShifts = SHIFTS[elementBits];
          int base = bitPos * FAC_BITPOS;
          currentShifts[base    ] = bitPos;
          currentShifts[base + 1] = BLOCK_SIZE - elementBits;
          if (bitPos <= BLOCK_SIZE - elementBits) { // Single block
            currentShifts[base + 2] = 0;
            MASKS[elementBits][bitPos] = 0;
          } else { // Two blocks
            int rBits = elementBits - (BLOCK_SIZE - bitPos);
            currentShifts[base + 2] = BLOCK_SIZE - rBits;
            MASKS[elementBits][bitPos] = ~(~0 << rBits);
          }
        }
      }
    }
  
    /*
     * The setter requires more masking than the getter.
    */
    private static final int[][] WRITE_MASKS =
            new int[ENTRY_SIZE][ENTRY_SIZE * FAC_BITPOS];
    static {
      for (int elementBits = 1 ; elementBits <= BLOCK_SIZE ; elementBits++) {
        int elementPosMask = ~(~0 << elementBits);
        int[] currentShifts = SHIFTS[elementBits];
        int[] currentMasks = WRITE_MASKS[elementBits];
        for (int bitPos = 0 ; bitPos < BLOCK_SIZE ; bitPos++) {
          int base = bitPos * FAC_BITPOS;
          currentMasks[base  ] =~((elementPosMask
                  << currentShifts[base + 1])
                  >>> currentShifts[base]);
          if (bitPos <= BLOCK_SIZE - elementBits) { // Second block not used
            currentMasks[base+1] = ~0; // Keep all bits
            currentMasks[base+2] = 0;  // Or with 0
          } else {
            currentMasks[base+1] = ~(elementPosMask
                                     << currentShifts[base + 2]);
            currentMasks[base+2] = currentShifts[base + 2] == 0 ? 0 : ~0;
          }
        }
      }
    }
  
    /* The bits */
    private int[] blocks;
  
    // Cached calculations
    private int maxPos;      // blocks.length * BLOCK_SIZE / bitsPerValue - 1
    private int[] shifts;    // The shifts for the current bitsPerValue
    private int[] readMasks;
    private int[] writeMasks;
  
    /**
     * Creates an array with the internal structures adjusted for the given
     * limits and initialized to 0.
     * @param valueCount   the number of elements.
     * @param bitsPerValue the number of bits available for any given value.
     *        Note: bitsPerValue >32 is not supported by this implementation.
     */
    public Packed32(int valueCount, int bitsPerValue) {
      this(new int[(int)(((long)valueCount) * bitsPerValue / BLOCK_SIZE + 2)],
              valueCount, bitsPerValue);
    }
  
    /**
     * Creates an array with content retrieved from the given DataInput.
     * @param in       a DataInput, positioned at the start of Packed64-content.
     * @param valueCount  the number of elements.
     * @param bitsPerValue the number of bits available for any given value.
     * @throws java.io.IOException if the values for the backing array could not
     *                             be retrieved.
     */
    public Packed32(DataInput in, int valueCount, int bitsPerValue)
                                                              throws IOException {
      super(valueCount, bitsPerValue);
      int size = size(bitsPerValue, valueCount);
      blocks = new int[size + 1]; // +1 due to non-conditional tricks
      // TODO: find a faster way to bulk-read ints...
      for(int i = 0 ; i < size ; i++) {
        blocks[i] = in.readInt();
      }
      if (size % 2 == 1) {
        in.readInt(); // Align to long
      }
      updateCached();
    }
  
    private static int size(int bitsPerValue, int valueCount) {
      final long totBitCount = (long) valueCount * bitsPerValue;
      return (int) (totBitCount/32 + ((totBitCount % 32 == 0 ) ? 0:1));
    }
  
  
    /**
     * Creates an array backed by the given blocks.
     * </p><p>
     * Note: The blocks are used directly, so changes to the given block will
     * affect the Packed32-structure.
     * @param blocks   used as the internal backing array.
     * @param valueCount   the number of values.
     * @param bitsPerValue the number of bits available for any given value.
     *        Note: bitsPerValue >32 is not supported by this implementation.
     */
    public Packed32(int[] blocks, int valueCount, int bitsPerValue) {
      // TODO: Check that blocks.length is sufficient for holding length values
      super(valueCount, bitsPerValue);
      if (bitsPerValue > 31) {
        throw new IllegalArgumentException(String.format(
                "This array only supports values of 31 bits or less. The "
                        + "required number of bits was %d. The Packed64 "
                        + "implementation allows values with more than 31 bits",
                bitsPerValue));
      }
      this.blocks = blocks;
      updateCached();
    }
  
    private void updateCached() {
      readMasks = MASKS[bitsPerValue];
      maxPos = (int)((((long)blocks.length) * BLOCK_SIZE / bitsPerValue) - 2);
      shifts = SHIFTS[bitsPerValue];
      writeMasks = WRITE_MASKS[bitsPerValue];
    }
  
    /**
     * @param index the position of the value.
     * @return the value at the given index.
     */
    public long get(final int index) {
      final long majorBitPos = (long)index * bitsPerValue;
      final int elementPos = (int)(majorBitPos >>> BLOCK_BITS); // / BLOCK_SIZE
      final int bitPos =     (int)(majorBitPos & MOD_MASK); // % BLOCK_SIZE);
  
      final int base = bitPos * FAC_BITPOS;
  
      return ((blocks[elementPos] << shifts[base]) >>> shifts[base+1]) |
              ((blocks[elementPos+1] >>> shifts[base+2]) & readMasks[bitPos]);
    }
  
    public void set(final int index, final long value) {
      final int intValue = (int)value;
      final long majorBitPos = (long)index * bitsPerValue;
      final int elementPos = (int)(majorBitPos >>> BLOCK_BITS); // / BLOCK_SIZE
      final int bitPos =     (int)(majorBitPos & MOD_MASK); // % BLOCK_SIZE);
      final int base = bitPos * FAC_BITPOS;
  
      blocks[elementPos  ] = (blocks[elementPos  ] & writeMasks[base])
              | (intValue << shifts[base + 1] >>> shifts[base]);
      blocks[elementPos+1] = (blocks[elementPos+1] & writeMasks[base+1])
              | ((intValue << shifts[base + 2])
              & writeMasks[base+2]);
    }
  
    public void clear() {
      Arrays.fill(blocks, 0);
    }
  
    @Override
    public String toString() {
      return "Packed32(bitsPerValue=" + bitsPerValue + ", maxPos=" + maxPos
              + ", elements.length=" + blocks.length + ")";
    }
  
    public long ramBytesUsed() {
      return RamUsageEstimator.NUM_BYTES_ARRAY_HEADER
              + blocks.length * RamUsageEstimator.NUM_BYTES_INT;
    }
  }
  