/*
    * This file is part of Waarp Project (named also Waarp or GG).
    *
    *  Copyright (c) 2019, Waarp SAS, and individual contributors by the @author
    *  tags. See the COPYRIGHT.txt in the distribution for a full listing of
    * individual contributors.
    *
    *  All Waarp Project is free software: you can redistribute it and/or
    * modify it under the terms of the GNU General Public License as published by
   * the Free Software Foundation, either version 3 of the License, or (at your
   * option) any later version.
   *
   * Waarp is distributed in the hope that it will be useful, but WITHOUT ANY
   * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License along with
   * Waarp . If not, see <http://www.gnu.org/licenses/>.
   */
  
  /*
   * 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.
   */
  package org.waarp.compress.zstdunsafe;
  
  import static java.lang.Long.*;
  
  // forked from https://github.com/airlift/slice
  final class XxHash64 {
    private static final long PRIME64_1 = 0x9E3779B185EBCA87L;
    private static final long PRIME64_2 = 0xC2B2AE3D27D4EB4FL;
    private static final long PRIME64_3 = 0x165667B19E3779F9L;
    private static final long PRIME64_4 = 0x85EBCA77C2b2AE63L;
    private static final long PRIME64_5 = 0x27D4EB2F165667C5L;
  
    private XxHash64() {
    }
  
    public static long hash(final long seed, final Object base,
                            final long address, final int length) {
      long hash;
      if (length >= 32) {
        hash = updateBody(seed, base, address, length);
      } else {
        hash = seed + PRIME64_5;
      }
  
      hash += length;
  
      // round to the closest 32 byte boundary
      // this is the point up to which updateBody() processed
      final int index = length & 0xFFFFFFE0;
  
      return updateTail(hash, base, address, index, length);
    }
  
    private static long updateTail(long hash, final Object base,
                                   final long address, int index,
                                   final int length) {
      while (index <= length - 8) {
        hash = updateTail(hash, UnsafeUtil.UNSAFE.getLong(base, address + index));
        index += 8;
      }
  
      if (index <= length - 4) {
        hash = updateTail(hash, UnsafeUtil.UNSAFE.getInt(base, address + index));
        index += 4;
      }
  
      while (index < length) {
        hash = updateTail(hash, UnsafeUtil.UNSAFE.getByte(base, address + index));
        index++;
      }
  
      hash = finalShuffle(hash);
  
      return hash;
    }
  
    private static long updateBody(final long seed, final Object base,
                                   long address, final int length) {
      long v1 = seed + PRIME64_1 + PRIME64_2;
      long v2 = seed + PRIME64_2;
      long v3 = seed;
      long v4 = seed - PRIME64_1;
  
      int remaining = length;
      while (remaining >= 32) {
        v1 = mix(v1, UnsafeUtil.UNSAFE.getLong(base, address));
       v2 = mix(v2, UnsafeUtil.UNSAFE.getLong(base, address + 8));
       v3 = mix(v3, UnsafeUtil.UNSAFE.getLong(base, address + 16));
       v4 = mix(v4, UnsafeUtil.UNSAFE.getLong(base, address + 24));
 
       address += 32;
       remaining -= 32;
     }
 
     long hash = rotateLeft(v1, 1) + rotateLeft(v2, 7) + rotateLeft(v3, 12) +
                 rotateLeft(v4, 18);
 
     hash = update(hash, v1);
     hash = update(hash, v2);
     hash = update(hash, v3);
     hash = update(hash, v4);
 
     return hash;
   }
 
   private static long mix(final long current, final long value) {
     return rotateLeft(current + value * PRIME64_2, 31) * PRIME64_1;
   }
 
   private static long update(final long hash, final long value) {
     final long temp = hash ^ mix(0, value);
     return temp * PRIME64_1 + PRIME64_4;
   }
 
   private static long updateTail(final long hash, final long value) {
     final long temp = hash ^ mix(0, value);
     return rotateLeft(temp, 27) * PRIME64_1 + PRIME64_4;
   }
 
   private static long updateTail(final long hash, final int value) {
     final long unsigned = value & 0xFFFFFFFFL;
     final long temp = hash ^ (unsigned * PRIME64_1);
     return rotateLeft(temp, 23) * PRIME64_2 + PRIME64_3;
   }
 
   private static long updateTail(final long hash, final byte value) {
     final int unsigned = value & 0xFF;
     final long temp = hash ^ (unsigned * PRIME64_5);
     return rotateLeft(temp, 11) * PRIME64_1;
   }
 
   private static long finalShuffle(long hash) {
     hash ^= hash >>> 33;
     hash *= PRIME64_2;
     hash ^= hash >>> 29;
     hash *= PRIME64_3;
     hash ^= hash >>> 32;
     return hash;
   }
 }