/*
 * 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.datasketches.memory.internal;

import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_BYTE_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_CHAR_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_DOUBLE_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_FLOAT_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_INT_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_LONG_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.ARRAY_SHORT_BASE_OFFSET;
import static org.apache.datasketches.memory.internal.UnsafeUtil.CHAR_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.DOUBLE_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.FLOAT_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.INT_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.LONG_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.SHORT_SHIFT;
import static org.apache.datasketches.memory.internal.UnsafeUtil.unsafe;

/**
 * The XxHash is a fast, non-cryptographic, 64-bit hash function that has
 * excellent avalanche and 2-way bit independence properties.
 * This java version adapted  the C++ version and the OpenHFT/Zero-Allocation-Hashing implementation
 * referenced below as inspiration.
 *
 * <p>The C++ source repository:
 * <a href="https://github.com/Cyan4973/xxHash">
 * https://github.com/Cyan4973/xxHash</a>. It has a BSD 2-Clause License:
 * <a href="http://www.opensource.org/licenses/bsd-license.php">
 * http://www.opensource.org/licenses/bsd-license.php</a>.  See LICENSE.
 *
 * <p>Portions of this code were adapted from
 * <a href="https://github.com/OpenHFT/Zero-Allocation-Hashing/blob/master/src/main/java/net/openhft/hashing/XxHash.java">
 * OpenHFT/Zero-Allocation-Hashing</a>, which has an Apache 2 license as does this site. See LICENSE.
 *
 * @author Lee Rhodes
 */
@SuppressWarnings("restriction")
public class XxHash64 {
  // Unsigned, 64-bit primes
  private static final long P1 = -7046029288634856825L;
  private static final long P2 = -4417276706812531889L;
  private static final long P3 =  1609587929392839161L;
  private static final long P4 = -8796714831421723037L;
  private static final long P5 =  2870177450012600261L;

  /**
   * Returns the 64-bit hash of the sequence of bytes in the unsafeObject specified by
   * <i>cumOffsetBytes</i>, <i>lengthBytes</i> and a <i>seed</i>.
   *
   * @param unsafeObj A reference to the object parameter required by unsafe. It may be null.
   * @param cumOffsetBytes cumulative offset in bytes of this object from the backing resource
   * including any user given offsetBytes. This offset may also include other offset components
   * such as the native off-heap memory address, DirectByteBuffer split offsets, region offsets,
   * and unsafe arrayBaseOffsets.
   * @param lengthBytes the length in bytes of the sequence to be hashed
   * @param seed a given seed
   * @return the 64-bit hash of the sequence of bytes in the unsafeObject specified by
   * <i>cumOffsetBytes</i>, <i>lengthBytes</i> and a <i>seed</i>.
   */
  static long hash(final Object unsafeObj, long cumOffsetBytes, final long lengthBytes,
      final long seed) {
    long hash;
    long remaining = lengthBytes;

    if (remaining >= 32) {
      long v1 = seed + P1 + P2;
      long v2 = seed + P2;
      long v3 = seed;
      long v4 = seed - P1;

      do {
        v1 += unsafe.getLong(unsafeObj, cumOffsetBytes) * P2;
        v1 = Long.rotateLeft(v1, 31);
        v1 *= P1;

        v2 += unsafe.getLong(unsafeObj, cumOffsetBytes + 8L) * P2;
        v2 = Long.rotateLeft(v2, 31);
        v2 *= P1;

        v3 += unsafe.getLong(unsafeObj, cumOffsetBytes + 16L) * P2;
        v3 = Long.rotateLeft(v3, 31);
        v3 *= P1;

        v4 += unsafe.getLong(unsafeObj, cumOffsetBytes + 24L) * P2;
        v4 = Long.rotateLeft(v4, 31);
        v4 *= P1;

        cumOffsetBytes += 32;
        remaining -= 32;
      } while (remaining >= 32);

      hash = Long.rotateLeft(v1, 1)
          + Long.rotateLeft(v2, 7)
          + Long.rotateLeft(v3, 12)
          + Long.rotateLeft(v4, 18);

      v1 *= P2;
      v1 = Long.rotateLeft(v1, 31);
      v1 *= P1;
      hash ^= v1;
      hash = (hash * P1) + P4;

      v2 *= P2;
      v2 = Long.rotateLeft(v2, 31);
      v2 *= P1;
      hash ^= v2;
      hash = (hash * P1) + P4;

      v3 *= P2;
      v3 = Long.rotateLeft(v3, 31);
      v3 *= P1;
      hash ^= v3;
      hash = (hash * P1) + P4;

      v4 *= P2;
      v4 = Long.rotateLeft(v4, 31);
      v4 *= P1;
      hash ^= v4;
      hash = (hash * P1) + P4;
    } //end remaining >= 32
    else {
      hash = seed + P5;
    }

    hash += lengthBytes;

    while (remaining >= 8) {
      long k1 = unsafe.getLong(unsafeObj, cumOffsetBytes);
      k1 *= P2;
      k1 = Long.rotateLeft(k1, 31);
      k1 *= P1;
      hash ^= k1;
      hash = (Long.rotateLeft(hash, 27) * P1) + P4;
      cumOffsetBytes += 8;
      remaining -= 8;
    }

    if (remaining >= 4) { //treat as unsigned ints
      hash ^= (unsafe.getInt(unsafeObj, cumOffsetBytes) & 0XFFFF_FFFFL) * P1;
      hash = (Long.rotateLeft(hash, 23) * P2) + P3;
      cumOffsetBytes += 4;
      remaining -= 4;
    }

    while (remaining != 0) { //treat as unsigned bytes
      hash ^= (unsafe.getByte(unsafeObj, cumOffsetBytes) & 0XFFL) * P5;
      hash = Long.rotateLeft(hash, 11) * P1;
      --remaining;
      ++cumOffsetBytes;
    }

    return finalize(hash);
  }

  /**
   * Returns a 64-bit hash from a single long. This method has been optimized for speed when only
   * a single hash of a long is required.
   * @param in A long.
   * @param seed A long valued seed.
   * @return the hash.
   */
  public static long hash(final long in, final long seed) {
    long hash = seed + P5;
    hash += 8;
    long k1 = in;
    k1 *= P2;
    k1 = Long.rotateLeft(k1, 31);
    k1 *= P1;
    hash ^= k1;
    hash = (Long.rotateLeft(hash, 27) * P1) + P4;
    return finalize(hash);
  }

  private static long finalize(long hash) {
    hash ^= hash >>> 33;
    hash *= P2;
    hash ^= hash >>> 29;
    hash *= P3;
    hash ^= hash >>> 32;
    return hash;
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetBytes starting at this offset
   * @param lengthBytes continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashBytes(final byte[] arr, final long offsetBytes,
      final long lengthBytes, final long seed) {
    return hash(arr, ARRAY_BYTE_BASE_OFFSET + offsetBytes, lengthBytes, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetShorts starting at this offset
   * @param lengthShorts continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashShorts(final short[] arr, final long offsetShorts,
      final long lengthShorts, final long seed) {
    return hash(arr, ARRAY_SHORT_BASE_OFFSET + (offsetShorts << SHORT_SHIFT),
        lengthShorts << SHORT_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetChars starting at this offset
   * @param lengthChars continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashChars(final char[] arr, final long offsetChars,
      final long lengthChars, final long seed) {
    return hash(arr, ARRAY_CHAR_BASE_OFFSET + (offsetChars << CHAR_SHIFT),
        lengthChars << CHAR_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetInts starting at this offset
   * @param lengthInts continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashInts(final int[] arr, final long offsetInts,
      final long lengthInts, final long seed) {
    return hash(arr, ARRAY_INT_BASE_OFFSET + (offsetInts << INT_SHIFT),
        lengthInts << INT_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetLongs starting at this offset
   * @param lengthLongs continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashLongs(final long[] arr, final long offsetLongs,
      final long lengthLongs, final long seed) {
    return hash(arr, ARRAY_LONG_BASE_OFFSET + (offsetLongs << LONG_SHIFT),
        lengthLongs << LONG_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetFloats starting at this offset
   * @param lengthFloats continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashFloats(final float[] arr, final long offsetFloats,
      final long lengthFloats, final long seed) {
    return hash(arr, ARRAY_FLOAT_BASE_OFFSET + (offsetFloats << FLOAT_SHIFT),
        lengthFloats << FLOAT_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param arr the given array
   * @param offsetDoubles starting at this offset
   * @param lengthDoubles continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashDoubles(final double[] arr, final long offsetDoubles,
      final long lengthDoubles, final long seed) {
    return hash(arr, ARRAY_DOUBLE_BASE_OFFSET + (offsetDoubles << DOUBLE_SHIFT),
        lengthDoubles << DOUBLE_SHIFT, seed);
  }

  /**
   * Hash the given arr starting at the given offset and continuing for the given length using the
   * given seed.
   * @param str the given string
   * @param offsetChars starting at this offset
   * @param lengthChars continuing for this length
   * @param seed the given seed
   * @return the hash
   */
  public static long hashString(final String str, final long offsetChars,
      final long lengthChars, final long seed) {
    return hashChars(str.toCharArray(), offsetChars, lengthChars, seed);
  }

}

