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;
 }

}