src/util/hash/MurmurHash3.java

package util.hash;

/**
 *  The MurmurHash3 algorithm was created by Austin Appleby and placed in the public domain.
 *  This java port was authored by Yonik Seeley and also placed into the public domain.
 *  The author hereby disclaims copyright to this source code.
 *  <p>
 *  This produces exactly the same hash values as the final C++
 *  version of MurmurHash3 and is thus suitable for producing the same hash values across
 *  platforms.
 *  <p>
 *  The 32 bit x86 version of this hash should be the fastest variant for relatively short keys like ids.
 *  murmurhash3_x64_128 is a good choice for longer strings or if you need more than 32 bits of hash.
 *  <p>
 *  Note - The x86 and x64 versions do _not_ produce the same results, as the
 *  algorithms are optimized for their respective platforms.
 *  <p>
 *  See http://github.com/yonik/java_util for future updates to this file.
 */
public final class MurmurHash3 {

  /** 128 bits of state */
  public static final class LongPair {
    public long val1;
    public long val2;
  }

  public static final int fmix32(int h) {
    h ^= h >>> 16;
    h *= 0x85ebca6b;
    h ^= h >>> 13;
    h *= 0xc2b2ae35;
    h ^= h >>> 16;
    return h;
  }

  public static final long fmix64(long k) {
    k ^= k >>> 33;
    k *= 0xff51afd7ed558ccdL;
    k ^= k >>> 33;
    k *= 0xc4ceb9fe1a85ec53L;
    k ^= k >>> 33;
    return k;
  }

  /** Gets a long from a byte buffer in little endian byte order. */
  public static final long getLongLittleEndian(byte[] buf, int offset) {
    return     ((long)buf[offset+7]    << 56)   // no mask needed
            | ((buf[offset+6] & 0xffL) << 48)
            | ((buf[offset+5] & 0xffL) << 40)
            | ((buf[offset+4] & 0xffL) << 32)
            | ((buf[offset+3] & 0xffL) << 24)
            | ((buf[offset+2] & 0xffL) << 16)
            | ((buf[offset+1] & 0xffL) << 8)
            | ((buf[offset  ] & 0xffL));        // no shift needed
  }


  /** Returns the MurmurHash3_x86_32 hash. */
  @SuppressWarnings("fallthrough")
  public static int murmurhash3_x86_32(byte[] data, int offset, int len, int seed) {

    final int c1 = 0xcc9e2d51;
    final int c2 = 0x1b873593;

    int h1 = seed;
    int roundedEnd = offset + (len & 0xfffffffc);  // round down to 4 byte block

    for (int i=offset; i<roundedEnd; i+=4) {
      // little endian load order
      int k1 = (data[i] & 0xff) | ((data[i+1] & 0xff) << 8) | ((data[i+2] & 0xff) << 16) | (data[i+3] << 24);
      k1 *= c1;
      k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
      k1 *= c2;

      h1 ^= k1;
      h1 = (h1 << 13) | (h1 >>> 19);  // ROTL32(h1,13);
      h1 = h1*5+0xe6546b64;
    }

    // tail
    int k1 = 0;

    switch(len & 0x03) {
      case 3:
        k1 = (data[roundedEnd + 2] & 0xff) << 16;
        // fallthrough
      case 2:
        k1 |= (data[roundedEnd + 1] & 0xff) << 8;
        // fallthrough
      case 1:
        k1 |= (data[roundedEnd] & 0xff);
        k1 *= c1;
        k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
        k1 *= c2;
        h1 ^= k1;
    }

    // finalization
    h1 ^= len;

    // fmix(h1);
    h1 ^= h1 >>> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >>> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >>> 16;

    return h1;
  }


  /** Returns the MurmurHash3_x86_32 hash of the UTF-8 bytes of the String without actually encoding
   * the string to a temporary buffer.  This is more than 2x faster than hashing the result
   * of String.getBytes().
   */
  public static int murmurhash3_x86_32(CharSequence data, int offset, int len, int seed) {

    final int c1 = 0xcc9e2d51;
    final int c2 = 0x1b873593;

    int h1 = seed;

    int pos = offset;
    int end = offset + len;
    int k1 = 0;
    int k2 = 0;
    int shift = 0;
    int bits = 0;
    int nBytes = 0;   // length in UTF8 bytes


    while (pos < end) {
      int code = data.charAt(pos++);
      if (code < 0x80) {
        k2 = code;
        bits = 8;

        /***
        // optimized ascii implementation (currently slower!!! code size?)
        if (shift == 24) {
          k1 = k1 | (code << 24);

          k1 *= c1;
          k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
          k1 *= c2;

          h1 ^= k1;
          h1 = (h1 << 13) | (h1 >>> 19);  // ROTL32(h1,13);
          h1 = h1*5+0xe6546b64;

          shift = 0;
          nBytes += 4;
          k1 = 0;
        } else {
          k1 |= code << shift;
          shift += 8;
        }
        continue;
       ***/

      }
      else if (code < 0x800) {
        k2 = (0xC0 | (code >> 6))
                | ((0x80 | (code & 0x3F)) << 8);
        bits = 16;
      }
      else if (code < 0xD800 || code > 0xDFFF || pos>=end) {
        // we check for pos>=end to encode an unpaired surrogate as 3 bytes.
        k2 = (0xE0 | (code >> 12))
                | ((0x80 | ((code >> 6) & 0x3F)) << 8)
                | ((0x80 | (code & 0x3F)) << 16);
        bits = 24;
      } else {
        // surrogate pair
        // int utf32 = pos < end ? (int) data.charAt(pos++) : 0;
        int utf32 = (int) data.charAt(pos++);
        utf32 = ((code - 0xD7C0) << 10) + (utf32 & 0x3FF);
        k2 = (0xff & (0xF0 | (utf32 >> 18)))
             | ((0x80 | ((utf32 >> 12) & 0x3F))) << 8
             | ((0x80 | ((utf32 >> 6) & 0x3F))) << 16
             |  (0x80 | (utf32 & 0x3F)) << 24;
        bits = 32;
      }


      k1 |= k2 << shift;

      // int used_bits = 32 - shift;  // how many bits of k2 were used in k1.
      // int unused_bits = bits - used_bits; //  (bits-(32-shift)) == bits+shift-32  == bits-newshift

      shift += bits;
      if (shift >= 32) {
        // mix after we have a complete word

        k1 *= c1;
        k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
        k1 *= c2;

        h1 ^= k1;
        h1 = (h1 << 13) | (h1 >>> 19);  // ROTL32(h1,13);
        h1 = h1*5+0xe6546b64;

        shift -= 32;
        // unfortunately, java won't let you shift 32 bits off, so we need to check for 0
        if (shift != 0) {
          k1 = k2 >>> (bits-shift);   // bits used == bits - newshift
        } else {
          k1 = 0;
        }
        nBytes += 4;
      }

    } // inner

    // handle tail
    if (shift > 0) {
      nBytes += shift >> 3;
      k1 *= c1;
      k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
      k1 *= c2;
      h1 ^= k1;
    }

    // finalization
    h1 ^= nBytes;

    // fmix(h1);
    h1 ^= h1 >>> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >>> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >>> 16;

    return h1;
  }


  /** Returns the MurmurHash3_x64_128 hash, placing the result in "out". */
  @SuppressWarnings("fallthrough")
  public static void murmurhash3_x64_128(byte[] key, int offset, int len, int seed, LongPair out) {
    // The original algorithm does have a 32 bit unsigned seed.
    // We have to mask to match the behavior of the unsigned types and prevent sign extension.
    long h1 = seed & 0x00000000FFFFFFFFL;
    long h2 = seed & 0x00000000FFFFFFFFL;

    final long c1 = 0x87c37b91114253d5L;
    final long c2 = 0x4cf5ad432745937fL;

    int roundedEnd = offset + (len & 0xFFFFFFF0);  // round down to 16 byte block
    for (int i=offset; i<roundedEnd; i+=16) {
        long k1 = getLongLittleEndian(key, i);
        long k2 = getLongLittleEndian(key, i+8);
        k1 *= c1; k1  = Long.rotateLeft(k1,31); k1 *= c2; h1 ^= k1;
        h1 = Long.rotateLeft(h1,27); h1 += h2; h1 = h1*5+0x52dce729;
        k2 *= c2; k2  = Long.rotateLeft(k2,33); k2 *= c1; h2 ^= k2;
        h2 = Long.rotateLeft(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
    }

    long k1 = 0;
    long k2 = 0;

    switch (len & 15) {
      case 15: k2  = (key[roundedEnd+14] & 0xffL) << 48;
      case 14: k2 |= (key[roundedEnd+13] & 0xffL) << 40;
      case 13: k2 |= (key[roundedEnd+12] & 0xffL) << 32;
      case 12: k2 |= (key[roundedEnd+11] & 0xffL) << 24;
      case 11: k2 |= (key[roundedEnd+10] & 0xffL) << 16;
      case 10: k2 |= (key[roundedEnd+ 9] & 0xffL) << 8;
      case  9: k2 |= (key[roundedEnd+ 8] & 0xffL);
        k2 *= c2; k2  = Long.rotateLeft(k2, 33); k2 *= c1; h2 ^= k2;
      case  8: k1  = ((long)key[roundedEnd+7]) << 56;
      case  7: k1 |= (key[roundedEnd+6] & 0xffL) << 48;
      case  6: k1 |= (key[roundedEnd+5] & 0xffL) << 40;
      case  5: k1 |= (key[roundedEnd+4] & 0xffL) << 32;
      case  4: k1 |= (key[roundedEnd+3] & 0xffL) << 24;
      case  3: k1 |= (key[roundedEnd+2] & 0xffL) << 16;
      case  2: k1 |= (key[roundedEnd+1] & 0xffL) << 8;
      case  1: k1 |= (key[roundedEnd  ] & 0xffL);
        k1 *= c1; k1  = Long.rotateLeft(k1,31); k1 *= c2; h1 ^= k1;
    }

    //----------
    // finalization

    h1 ^= len; h2 ^= len;

    h1 += h2;
    h2 += h1;

    h1 = fmix64(h1);
    h2 = fmix64(h2);

    h1 += h2;
    h2 += h1;

    out.val1 = h1;
    out.val2 = h2;
  }

}