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Java example source code file (altHashing.cpp)

This example Java source code file (altHashing.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

althashing::murmur3_32, althashing\:\:compute_seed, althashing\:\:test_alt_hash, althashing\:\:testequivalenthashes, eight_byte, expected, four_char, hashes, integer_rotateleft, murmur3_32_x86_check_value, one_byte, one_char, product, three_byte

The altHashing.cpp Java example source code

/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "classfile/altHashing.hpp"
#include "classfile/symbolTable.hpp"
#include "classfile/systemDictionary.hpp"
#include "oops/markOop.hpp"
#include "runtime/thread.hpp"

// Get the hash code of the classes mirror if it exists, otherwise just
// return a random number, which is one of the possible hash code used for
// objects.  We don't want to call the synchronizer hash code to install
// this value because it may safepoint.
intptr_t object_hash(Klass* k) {
  intptr_t hc = k->java_mirror()->mark()->hash();
  return hc != markOopDesc::no_hash ? hc : os::random();
}

// Seed value used for each alternative hash calculated.
jint AltHashing::compute_seed() {
  jlong nanos = os::javaTimeNanos();
  jlong now = os::javaTimeMillis();
  jint SEED_MATERIAL[8] = {
            (jint) object_hash(SystemDictionary::String_klass()),
            (jint) object_hash(SystemDictionary::System_klass()),
            (jint) os::random(),  // current thread isn't a java thread
            (jint) (((julong)nanos) >> 32),
            (jint) nanos,
            (jint) (((julong)now) >> 32),
            (jint) now,
            (jint) (os::javaTimeNanos() >> 2)
  };

  return murmur3_32(SEED_MATERIAL, 8);
}


// Murmur3 hashing for Symbol
jint AltHashing::murmur3_32(jint seed, const jbyte* data, int len) {
  jint h1 = seed;
  int count = len;
  int offset = 0;

  // body
  while (count >= 4) {
    jint k1 = (data[offset] & 0x0FF)
        | (data[offset + 1] & 0x0FF) << 8
        | (data[offset + 2] & 0x0FF) << 16
        | data[offset + 3] << 24;

    count -= 4;
    offset += 4;

    k1 *= 0xcc9e2d51;
    k1 = Integer_rotateLeft(k1, 15);
    k1 *= 0x1b873593;

    h1 ^= k1;
    h1 = Integer_rotateLeft(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
  }

  // tail

  if (count > 0) {
    jint k1 = 0;

    switch (count) {
      case 3:
        k1 ^= (data[offset + 2] & 0xff) << 16;
      // fall through
      case 2:
        k1 ^= (data[offset + 1] & 0xff) << 8;
      // fall through
      case 1:
        k1 ^= (data[offset] & 0xff);
      // fall through
      default:
        k1 *= 0xcc9e2d51;
        k1 = Integer_rotateLeft(k1, 15);
        k1 *= 0x1b873593;
        h1 ^= k1;
    }
  }

  // finalization
  h1 ^= len;

  // finalization mix force all bits of a hash block to avalanche
  h1 ^= ((unsigned int)h1) >> 16;
  h1 *= 0x85ebca6b;
  h1 ^= ((unsigned int)h1) >> 13;
  h1 *= 0xc2b2ae35;
  h1 ^= ((unsigned int)h1) >> 16;

  return h1;
}

// Murmur3 hashing for Strings
jint AltHashing::murmur3_32(jint seed, const jchar* data, int len) {
  jint h1 = seed;

  int off = 0;
  int count = len;

  // body
  while (count >= 2) {
    jchar d1 = data[off++] & 0xFFFF;
    jchar d2 = data[off++];
    jint k1 = (d1 | d2 << 16);

    count -= 2;

    k1 *= 0xcc9e2d51;
    k1 = Integer_rotateLeft(k1, 15);
    k1 *= 0x1b873593;

    h1 ^= k1;
    h1 = Integer_rotateLeft(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
  }

  // tail

  if (count > 0) {
    int k1 = data[off];

    k1 *= 0xcc9e2d51;
    k1 = Integer_rotateLeft(k1, 15);
    k1 *= 0x1b873593;
    h1 ^= k1;
  }

  // finalization
  h1 ^= len * 2; // (Character.SIZE / Byte.SIZE);

  // finalization mix force all bits of a hash block to avalanche
  h1 ^= ((unsigned int)h1) >> 16;
  h1 *= 0x85ebca6b;
  h1 ^= ((unsigned int)h1) >> 13;
  h1 *= 0xc2b2ae35;
  h1 ^= ((unsigned int)h1) >> 16;

  return h1;
}

// Hash used for the seed.
jint AltHashing::murmur3_32(jint seed, const int* data, int len) {
  jint h1 = seed;

  int off = 0;
  int end = len;

  // body
  while (off < end) {
    jint k1 = data[off++];

    k1 *= 0xcc9e2d51;
    k1 = Integer_rotateLeft(k1, 15);
    k1 *= 0x1b873593;

    h1 ^= k1;
    h1 = Integer_rotateLeft(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
  }

  // tail (always empty, as body is always 32-bit chunks)

  // finalization

  h1 ^= len * 4; // (Integer.SIZE / Byte.SIZE);

  // finalization mix force all bits of a hash block to avalanche
  h1 ^= ((juint)h1) >> 16;
  h1 *= 0x85ebca6b;
  h1 ^= ((juint)h1) >> 13;
  h1 *= 0xc2b2ae35;
  h1 ^= ((juint)h1) >> 16;

  return h1;
}

jint AltHashing::murmur3_32(const int* data, int len) {
  return murmur3_32(0, data, len);
}

#ifndef PRODUCT
// Overloaded versions for internal test.
jint AltHashing::murmur3_32(const jbyte* data, int len) {
  return murmur3_32(0, data, len);
}

jint AltHashing::murmur3_32(const jchar* data, int len) {
  return murmur3_32(0, data, len);
}

// Internal test for alternate hashing.  Translated from JDK version
// test/sun/misc/Hashing.java
static const jbyte ONE_BYTE[] = { (jbyte) 0x80};
static const jbyte TWO_BYTE[] = { (jbyte) 0x80, (jbyte) 0x81};
static const jchar ONE_CHAR[] = { (jchar) 0x8180};
static const jbyte THREE_BYTE[] = { (jbyte) 0x80, (jbyte) 0x81, (jbyte) 0x82};
static const jbyte FOUR_BYTE[] = { (jbyte) 0x80, (jbyte) 0x81, (jbyte) 0x82, (jbyte) 0x83};
static const jchar TWO_CHAR[] = { (jchar) 0x8180, (jchar) 0x8382};
static const jint ONE_INT[] = { 0x83828180};
static const jbyte SIX_BYTE[] = { (jbyte) 0x80, (jbyte) 0x81, (jbyte) 0x82, (jbyte) 0x83, (jbyte) 0x84, (jbyte) 0x85};
static const jchar THREE_CHAR[] = { (jchar) 0x8180, (jchar) 0x8382, (jchar) 0x8584};
static const jbyte EIGHT_BYTE[] = {
  (jbyte) 0x80, (jbyte) 0x81, (jbyte) 0x82,
  (jbyte) 0x83, (jbyte) 0x84, (jbyte) 0x85,
  (jbyte) 0x86, (jbyte) 0x87};
static const jchar FOUR_CHAR[] = {
  (jchar) 0x8180, (jchar) 0x8382,
  (jchar) 0x8584, (jchar) 0x8786};

static const jint TWO_INT[] = { 0x83828180, 0x87868584};

static const juint MURMUR3_32_X86_CHECK_VALUE = 0xB0F57EE3;

void AltHashing::testMurmur3_32_ByteArray() {
  // printf("testMurmur3_32_ByteArray\n");

  jbyte vector[256];
  jbyte hashes[4 * 256];

  for (int i = 0; i < 256; i++) {
    vector[i] = (jbyte) i;
  }

  // Hash subranges {}, {0}, {0,1}, {0,1,2}, ..., {0,...,255}
  for (int i = 0; i < 256; i++) {
    jint hash = murmur3_32(256 - i, vector, i);
    hashes[i * 4] = (jbyte) hash;
    hashes[i * 4 + 1] = (jbyte) (((juint)hash) >> 8);
    hashes[i * 4 + 2] = (jbyte) (((juint)hash) >> 16);
    hashes[i * 4 + 3] = (jbyte) (((juint)hash) >> 24);
  }

  // hash to get const result.
  juint final_hash = murmur3_32(hashes, 4*256);

  assert (MURMUR3_32_X86_CHECK_VALUE == final_hash,
    err_msg(
        "Calculated hash result not as expected. Expected %08X got %08X\n",
        MURMUR3_32_X86_CHECK_VALUE,
        final_hash));
}

void AltHashing::testEquivalentHashes() {
  jint jbytes, jchars, ints;

  // printf("testEquivalentHashes\n");

  jbytes = murmur3_32(TWO_BYTE, 2);
  jchars = murmur3_32(ONE_CHAR, 1);
  assert (jbytes == jchars,
    err_msg("Hashes did not match. b:%08x != c:%08x\n", jbytes, jchars));

  jbytes = murmur3_32(FOUR_BYTE, 4);
  jchars = murmur3_32(TWO_CHAR, 2);
  ints = murmur3_32(ONE_INT, 1);
  assert ((jbytes == jchars) && (jbytes == ints),
    err_msg("Hashes did not match. b:%08x != c:%08x != i:%08x\n", jbytes, jchars, ints));

  jbytes = murmur3_32(SIX_BYTE, 6);
  jchars = murmur3_32(THREE_CHAR, 3);
  assert (jbytes == jchars,
    err_msg("Hashes did not match. b:%08x != c:%08x\n", jbytes, jchars));

  jbytes = murmur3_32(EIGHT_BYTE, 8);
  jchars = murmur3_32(FOUR_CHAR, 4);
  ints = murmur3_32(TWO_INT, 2);
  assert ((jbytes == jchars) && (jbytes == ints),
    err_msg("Hashes did not match. b:%08x != c:%08x != i:%08x\n", jbytes, jchars, ints));
}

// Returns true if the alternate hashcode is correct
void AltHashing::test_alt_hash() {
  testMurmur3_32_ByteArray();
  testEquivalentHashes();
}
#endif // PRODUCT

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