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/*
 * Licensed to Elasticsearch B.V. under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch B.V. licenses this file to you 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.
 */
/*
 * Copyright 2014-2020 Real Logic Limited.
 *
 * 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
 *
 * https://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.
 */
package co.elastic.otel.profiler.collections;

/** Hashing functions for applying to integers. */
public class Hashing {
  /** Default load factor to be used in open addressing hashed data structures. */
  public static final float DEFAULT_LOAD_FACTOR = 0.55f;

  /**
   * Generate a hash for an int value. This is a no op.
   *
   * @param value to be hashed.
   * @return the hashed value.
   */
  public static int hash(final int value) {
    return value * 31;
  }

  /**
   * Generate a hash for an long value.
   *
   * @param value to be hashed.
   * @return the hashed value.
   */
  public static int hash(final long value) {
    long hash = value * 31;
    hash = (int) hash ^ (int) (hash >>> 32);

    return (int) hash;
  }

  /**
   * Generate a hash for a int value.
   *
   * @param value to be hashed.
   * @param mask mask to be applied that must be a power of 2 - 1.
   * @return the hash of the value.
   */
  public static int hash(final int value, final int mask) {
    final int hash = value * 31;

    return hash & mask;
  }

  /**
   * Generate a hash for a K value.
   *
   * @param  is the type of value
   * @param value to be hashed.
   * @param mask mask to be applied that must be a power of 2 - 1.
   * @return the hash of the value.
   */
  public static  int hash(final K value, final int mask) {
    final int hash = value.hashCode();

    return hash & mask;
  }

  /**
   * Generate a hash for a long value.
   *
   * @param value to be hashed.
   * @param mask mask to be applied that must be a power of 2 - 1.
   * @return the hash of the value.
   */
  public static int hash(final long value, final int mask) {
    long hash = value * 31;
    hash = (int) hash ^ (int) (hash >>> 32);

    return (int) hash & mask;
  }

  /**
   * Generate an even hash for a int value.
   *
   * @param value to be hashed.
   * @param mask mask to be applied that must be a power of 2 - 1.
   * @return the hash of the value which is always even.
   */
  public static int evenHash(final int value, final int mask) {
    final int hash = (value << 1) - (value << 8);

    return hash & mask;
  }

  /**
   * Generate an even hash for a long value.
   *
   * @param value to be hashed.
   * @param mask mask to be applied that must be a power of 2 - 1.
   * @return the hash of the value which is always even.
   */
  public static int evenHash(final long value, final int mask) {
    int hash = (int) value ^ (int) (value >>> 32);
    hash = (hash << 1) - (hash << 8);

    return hash & mask;
  }

  /**
   * Combined two 32 bit keys into a 64-bit compound.
   *
   * @param keyPartA to make the upper bits
   * @param keyPartB to make the lower bits.
   * @return the compound key
   */
  public static long compoundKey(final int keyPartA, final int keyPartB) {
    return ((long) keyPartA << 32) | (keyPartB & 0xFFFF_FFFFL);
  }

  public static int hashCode(long value) {
    return (int) (value ^ (value >>> 32));
  }
}