src/hotspot/share/classfile/altHashing.cpp

/*
 * Copyright (c) 2012, 2025, 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.
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/*
 * halfsiphash code adapted from reference implementation
 * (https://github.com/veorq/SipHash/blob/master/halfsiphash.c)
 * which is distributed with the following copyright:
 */

/*
   SipHash reference C implementation

   Copyright (c) 2016 Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>

   To the extent possible under law, the author(s) have dedicated all copyright
   and related and neighboring rights to this software to the public domain
   worldwide. This software is distributed without any warranty.

   You should have received a copy of the CC0 Public Domain Dedication along
   with
   this software. If not, see
   <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#include "classfile/altHashing.hpp"
#include "classfile/vmClasses.hpp"
#include "oops/klass.inline.hpp"
#include "oops/markWord.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/os.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.
static intptr_t object_hash(Klass* k) {
  intptr_t hc = k->java_mirror()->mark().hash();
  return hc != markWord::no_hash ? hc : os::random();
}

// Seed value used for each alternative hash calculated.
uint64_t AltHashing::compute_seed() {
  uint64_t nanos = os::javaTimeNanos();
  uint64_t now = os::javaTimeMillis();
  uint32_t SEED_MATERIAL[8] = {
            (uint32_t) object_hash(vmClasses::String_klass()),
            (uint32_t) object_hash(vmClasses::System_klass()),
            (uint32_t) os::random(),  // current thread isn't a java thread
            (uint32_t) (((uint64_t)nanos) >> 32),
            (uint32_t) nanos,
            (uint32_t) (((uint64_t)now) >> 32),
            (uint32_t) now,
            (uint32_t) (os::javaTimeNanos() >> 2)
  };

  return halfsiphash_64(SEED_MATERIAL, 8);
}

// utility function copied from java/lang/Integer
static uint32_t Integer_rotateLeft(uint32_t i, int distance) {
  return (i << distance) | (i >> (32 - distance));
}

static void halfsiphash_rounds(uint32_t v[4], int rounds) {
  while (rounds-- > 0) {
    v[0] += v[1];
    v[1] = Integer_rotateLeft(v[1], 5);
    v[1] ^= v[0];
    v[0] = Integer_rotateLeft(v[0], 16);
    v[2] += v[3];
    v[3] = Integer_rotateLeft(v[3], 8);
    v[3] ^= v[2];
    v[0] += v[3];
    v[3] = Integer_rotateLeft(v[3], 7);
    v[3] ^= v[0];
    v[2] += v[1];
    v[1] = Integer_rotateLeft(v[1], 13);
    v[1] ^= v[2];
    v[2] = Integer_rotateLeft(v[2], 16);
  }
}

static void halfsiphash_adddata(uint32_t v[4], uint32_t newdata, int rounds) {
  v[3] ^= newdata;
  halfsiphash_rounds(v, rounds);
  v[0] ^= newdata;
}

static void halfsiphash_init32(uint32_t v[4], uint64_t seed) {
  v[0] = seed & 0xffffffff;
  v[1] = (uint32_t)(seed >> 32);
  v[2] = 0x6c796765 ^ v[0];
  v[3] = 0x74656462 ^ v[1];
}

static void halfsiphash_init64(uint32_t v[4], uint64_t seed) {
  halfsiphash_init32(v, seed);
  v[1] ^= 0xee;
}

static uint32_t halfsiphash_finish32(uint32_t v[4], int rounds) {
  v[2] ^= 0xff;
  halfsiphash_rounds(v, rounds);
  return (v[1] ^ v[3]);
}

static uint64_t halfsiphash_finish64(uint32_t v[4], int rounds) {
  uint64_t rv;
  v[2] ^= 0xee;
  halfsiphash_rounds(v, rounds);
  rv = v[1] ^ v[3];
  v[1] ^= 0xdd;
  halfsiphash_rounds(v, rounds);
  rv |= (uint64_t)(v[1] ^ v[3]) << 32;
  return rv;
}

// HalfSipHash-2-4 (32-bit output) for Symbols
uint32_t AltHashing::halfsiphash_32(uint64_t seed, const void* in, int len) {

  const unsigned char* data = (const unsigned char*)in;
  uint32_t v[4];
  uint32_t newdata;
  int off = 0;
  int count = len;

  halfsiphash_init32(v, seed);

  // body
  while (count >= 4) {

    // Avoid sign extension with 0x0ff
    newdata = (data[off] & 0x0FF)
        | (data[off + 1] & 0x0FF) << 8
        | (data[off + 2] & 0x0FF) << 16
        | data[off + 3] << 24;

    count -= 4;
    off += 4;

    halfsiphash_adddata(v, newdata, 2);
  }

  // tail
  newdata = ((uint32_t)len) << 24; // (Byte.SIZE / Byte.SIZE);

  if (count > 0) {
    switch (count) {
      case 3:
        newdata |= (data[off + 2] & 0x0ff) << 16;
      // fall through
      case 2:
        newdata |= (data[off + 1] & 0x0ff) << 8;
      // fall through
      case 1:
        newdata |= (data[off] & 0x0ff);
      // fall through
    }
  }

  halfsiphash_adddata(v, newdata, 2);

  // finalization
  return halfsiphash_finish32(v, 4);
}

// HalfSipHash-2-4 (32-bit output) for Strings
uint32_t AltHashing::halfsiphash_32(uint64_t seed, const uint16_t* data, int len) {
  uint32_t v[4];
  uint32_t newdata;
  int off = 0;
  int count = len;

  halfsiphash_init32(v, seed);

  // body
  while (count >= 2) {
    uint16_t d1 = data[off++] & 0x0FFFF;
    uint16_t d2 = data[off++];
    newdata = (d1 | d2 << 16);

    count -= 2;

    halfsiphash_adddata(v, newdata, 2);
  }

  // tail
  newdata = ((uint32_t)len * 2) << 24; // (Character.SIZE / Byte.SIZE);
  if (count > 0) {
    newdata |= (uint32_t)data[off];
  }
  halfsiphash_adddata(v, newdata, 2);

  // finalization
  return halfsiphash_finish32(v, 4);
}

// HalfSipHash-2-4 (64-bit output) for integers (used to create seed)
uint64_t AltHashing::halfsiphash_64(uint64_t seed, const uint32_t* data, int len) {
  uint32_t v[4];

  int off = 0;
  int end = len;

  halfsiphash_init64(v, seed);

  // body
  while (off < end) {
    halfsiphash_adddata(v, (uint32_t)data[off++], 2);
  }

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

  // finalization
  halfsiphash_adddata(v, ((uint32_t)len * 4) << 24, 2); // (Integer.SIZE / Byte.SIZE);
  return halfsiphash_finish64(v, 4);
}

// HalfSipHash-2-4 (64-bit output) for integers (used to create seed)
uint64_t AltHashing::halfsiphash_64(const uint32_t* data, int len) {
  return halfsiphash_64((uint64_t)0, data, len);
}