/*
    * Copyright (C) 2012 The Guava Authors
    *
    * 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.
   */
  
  /*
   * SipHash-c-d was designed by Jean-Philippe Aumasson and Daniel J. Bernstein and is described in
   * "SipHash: a fast short-input PRF" (available at https://131002.net/siphash/siphash.pdf).
   */
  
  package com.google.common.hash;
  
  import static com.google.common.base.Preconditions.checkArgument;
  
  import java.io.Serializable;
  import java.nio.ByteBuffer;
  
  import javax.annotation.Nullable;
  
  /**
   * {@link HashFunction} implementation of SipHash-c-d.
   *
   * @author Kurt Alfred Kluever
   * @author Jean-Philippe Aumasson
   * @author Daniel J. Bernstein
   */
  final class SipHashFunction extends AbstractStreamingHashFunction implements Serializable {
  
    // The number of compression rounds.
    private final int c;
    // The number of finalization rounds.
    private final int d;
    // Two 64-bit keys (represent a single 128-bit key).
    private final long k0;
    private final long k1;
  
    /**
     * @param c the number of compression rounds (must be positive)
     * @param d the number of finalization rounds (must be positive)
     * @param k0 the first half of the key
     * @param k1 the second half of the key
     */
    SipHashFunction(int c, int d, long k0, long k1) {
      checkArgument(c > 0,
          "The number of SipRound iterations (c=%s) during Compression must be positive.", c);
      checkArgument(d > 0,
          "The number of SipRound iterations (d=%s) during Finalization must be positive.", d);
      this.c = c;
      this.d = d;
      this.k0 = k0;
      this.k1 = k1;
    }
  
    @Override public int bits() {
      return 64;
    }
  
    @Override public Hasher newHasher() {
      return new SipHasher(c, d, k0, k1);
    }
  
    // TODO(user): Implement and benchmark the hashFoo() shortcuts.
  
    @Override public String toString() {
      return "Hashing.sipHash" + c + "" + d + "(" + k0 + ", " + k1 + ")";
    }
  
    @Override
    public boolean equals(@Nullable Object object) {
      if (object instanceof SipHashFunction) {
        SipHashFunction other = (SipHashFunction) object;
        return (c == other.c)
            && (d == other.d)
            && (k0 == other.k0)
            && (k1 == other.k1);
      }
      return false;
    }
  
    @Override
    public int hashCode() {
      return (int) (getClass().hashCode() ^ c ^ d ^ k0 ^ k1);
    }
  
    private static final class SipHasher extends AbstractStreamingHasher {
      private static final int CHUNK_SIZE = 8;
  
      // The number of compression rounds.
      private final int c;
      // The number of finalization rounds.
     private final int d;
 
     // Four 64-bit words of internal state.
     // The initial state corresponds to the ASCII string "somepseudorandomlygeneratedbytes",
     // big-endian encoded. There is nothing special about this value; the only requirement
     // was some asymmetry so that the initial v0 and v1 differ from v2 and v3.
     private long v0 = 0x736f6d6570736575L;
     private long v1 = 0x646f72616e646f6dL;
     private long v2 = 0x6c7967656e657261L;
     private long v3 = 0x7465646279746573L;
 
     // The number of bytes in the input.
     private long b = 0;
 
     // The final 64-bit chunk includes the last 0 through 7 bytes of m followed by null bytes
     // and ending with a byte encoding the positive integer b mod 256.
     private long finalM = 0;
 
     SipHasher(int c, int d, long k0, long k1) {
       super(CHUNK_SIZE);
       this.c = c;
       this.d = d;
       this.v0 ^= k0;
       this.v1 ^= k1;
       this.v2 ^= k0;
       this.v3 ^= k1;
     }
 
     @Override protected void process(ByteBuffer buffer) {
       b += CHUNK_SIZE;
       processM(buffer.getLong());
     }
 
     @Override protected void processRemaining(ByteBuffer buffer) {
       b += buffer.remaining();
       for (int i = 0; buffer.hasRemaining(); i += 8) {
         finalM ^= (buffer.get() & 0xFFL) << i;
       }
     }
 
     @Override public HashCode makeHash() {
       // End with a byte encoding the positive integer b mod 256.
       finalM ^= b << 56;
       processM(finalM);
 
       // Finalization
       v2 ^= 0xFFL;
       sipRound(d);
       return HashCode.fromLong(v0 ^ v1 ^ v2 ^ v3);
     }
 
     private void processM(long m) {
       v3 ^= m;
       sipRound(c);
       v0 ^= m;
     }
 
     private void sipRound(int iterations) {
       for (int i = 0; i < iterations; i++) {
         v0 += v1;
         v2 += v3;
         v1 = Long.rotateLeft(v1, 13);
         v3 = Long.rotateLeft(v3, 16);
         v1 ^= v0;
         v3 ^= v2;
         v0 = Long.rotateLeft(v0, 32);
         v2 += v1;
         v0 += v3;
         v1 = Long.rotateLeft(v1, 17);
         v3 = Long.rotateLeft(v3, 21);
         v1 ^= v2;
         v3 ^= v0;
         v2 = Long.rotateLeft(v2, 32);
       }
     }
   }
 
   private static final long serialVersionUID = 0L;
 }