content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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.
   */
  
  package org.apache.kafka.timeline;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * A hash table which uses separate chaining.
   * <br>
   * In order to optimize memory consumption a bit, the common case where there is
   * one element per slot is handled by simply placing the element in the slot,
   * and the case where there are multiple elements is handled by creating an
   * array and putting that in the slot. Java is storing type info in memory
   * about every object whether we want it or not, so let's get some benefit
   * out of it.
   * <br>
   * Arrays and null values cannot be inserted.
   */
  @SuppressWarnings("unchecked")
  class BaseHashTable<T> {
      /**
       * The maximum load factor we will allow the hash table to climb to before expanding.
       */
      private static final double MAX_LOAD_FACTOR = 0.75f;
  
      /**
       * The minimum number of slots we can have in the hash table.
       */
      static final int MIN_CAPACITY = 2;
  
      /**
       * The maximum number of slots we can have in the hash table.
       */
      static final int MAX_CAPACITY = 1 << 30;
  
      private Object[] elements;
      private int size = 0;
  
      BaseHashTable(int expectedSize) {
          this.elements = new Object[expectedSizeToCapacity(expectedSize)];
      }
  
      /**
       * Calculate the capacity we should provision, given the expected size.
       * <br>
       * Our capacity must always be a power of 2, and never less than 2 or more
       * than MAX_CAPACITY.  We use 64-bit numbers here to avoid overflow
       * concerns.
       */
      static int expectedSizeToCapacity(int expectedSize) {
          long minCapacity = (long) Math.ceil((float) expectedSize / MAX_LOAD_FACTOR);
          return Math.max(MIN_CAPACITY,
                  (int) Math.min(MAX_CAPACITY, roundUpToPowerOfTwo(minCapacity)));
      }
  
      private static long roundUpToPowerOfTwo(long i) {
          if (i <= 0) {
              return 0;
          } else if (i > (1L << 62)) {
              throw new ArithmeticException("There are no 63-bit powers of 2 higher than " +
                      "or equal to " + i);
          } else {
              return 1L << -Long.numberOfLeadingZeros(i - 1);
          }
      }
  
      final int baseSize() {
          return size;
      }
  
      final Object[] baseElements() {
          return elements;
      }
  
      final T baseGet(Object key) {
          int slot = findSlot(key, elements.length);
          Object value = elements[slot];
          if (value == null) {
              return null;
          } else if (value instanceof Object[]) {
              T[] array = (T[]) value;
              for (T object : array) {
                  if (object.equals(key)) {
                      return object;
                  }
              }
              return null;
          } else if (value.equals(key)) {
              return (T) value;
          } else {
              return null;
          }
      }
  
      final T baseAddOrReplace(T newObject) {
          if (((size + 1) * MAX_LOAD_FACTOR > elements.length) &&
                  (elements.length < MAX_CAPACITY)) {
              int newSize = elements.length * 2;
              rehash(newSize);
          }
          int slot = findSlot(newObject, elements.length);
          Object cur = elements[slot];
          if (cur == null) {
              size++;
              elements[slot] = newObject;
              return null;
          } else if (cur instanceof Object[]) {
              T[] curArray = (T[]) cur;
              for (int i =  0; i < curArray.length; i++) {
                  T value = curArray[i];
                  if (value.equals(newObject)) {
                      curArray[i] = newObject;
                      return value;
                  }
              }
              size++;
              T[] newArray = (T[]) new Object[curArray.length + 1];
              System.arraycopy(curArray, 0, newArray, 0, curArray.length);
              newArray[curArray.length] = newObject;
              elements[slot] = newArray;
              return null;
          } else if (cur.equals(newObject)) {
              elements[slot] = newObject;
              return (T) cur;
          } else {
              size++;
              elements[slot] = new Object[] {cur, newObject};
              return null;
          }
      }
  
      final T baseRemove(Object key) {
          int slot = findSlot(key, elements.length);
          Object object = elements[slot];
          if (object == null) {
              return null;
          } else if (object instanceof Object[] curArray) {
              for (int i = 0; i < curArray.length; i++) {
                  if (curArray[i].equals(key)) {
                      size--;
                      if (curArray.length <= 2) {
                          int j = i == 0 ? 1 : 0;
                          elements[slot] = curArray[j];
                      } else {
                          Object[] newArray = new Object[curArray.length - 1];
                          System.arraycopy(curArray, 0, newArray, 0, i);
                          System.arraycopy(curArray, i + 1, newArray, i, curArray.length - 1 - i);
                          elements[slot] = newArray;
                      }
                      return (T) curArray[i];
                  }
              }
              return null;
          } else if (object.equals(key)) {
              size--;
              elements[slot] = null;
              return (T) object;
          } else {
              return null;
          }
      }
  
      /**
       * Expand the hash table to a new size.  Existing elements will be copied to new slots.
       */
      private void rehash(int newSize) {
          Object[] prevElements = elements;
          elements = new Object[newSize];
          List<Object> ready = new ArrayList<>();
          for (int slot = 0; slot < prevElements.length; slot++) {
              unpackSlot(ready, prevElements, slot);
              for (Object object : ready) {
                  int newSlot = findSlot(object, elements.length);
                  Object cur = elements[newSlot];
                  if (cur == null) {
                      elements[newSlot] = object;
                  } else if (cur instanceof Object[] curArray) {
                      Object[] newArray = new Object[curArray.length + 1];
                      System.arraycopy(curArray, 0, newArray, 0, curArray.length);
                      newArray[curArray.length] = object;
                      elements[newSlot] = newArray;
                  } else {
                      elements[newSlot] = new Object[]{cur, object};
                  }
              }
              ready.clear();
          }
      }
  
      /**
       * Find the slot in the array that an element should go into.
       */
      static int findSlot(Object object, int numElements) {
          // This performs a secondary hash using Knuth's multiplicative Fibonacci
          // hashing.  Then, we choose some of the highest bits.  The number of bits
          // we choose is based on the table size.  If the size is 2, we need 1 bit;
          // if the size is 4, we need 2 bits, etc.
          int objectHashCode = object.hashCode();
          int log2size = 32 - Integer.numberOfLeadingZeros(numElements);
          int shift = 65 - log2size;
          return (int) ((objectHashCode * -7046029254386353131L) >>> shift);
      }
  
      /**
       * Copy any elements in the given slot into the output list.
       */
      static <T> void unpackSlot(List<T> out, Object[] elements, int slot) {
          Object value = elements[slot];
          if (value != null) {
              if (value instanceof Object[] array) {
                  for (Object object : array) {
                      out.add((T) object);
                  }
              } else {
                  out.add((T) value);
              }
          }
      }
  
      String baseToDebugString() {
          StringBuilder bld = new StringBuilder();
          bld.append("BaseHashTable{");
          for (int i = 0; i < elements.length; i++) {
              Object slotObject = elements[i];
              bld.append(String.format("%n%d: ", i));
              if (slotObject == null) {
                  bld.append("null");
              } else if (slotObject instanceof Object[] array) {
                  String prefix = "";
                  for (Object object : array) {
                      bld.append(prefix);
                      prefix = ", ";
                      bld.append(object);
                  }
              } else {
                  bld.append(slotObject);
              }
          }
          bld.append(String.format("%n}"));
          return bld.toString();
      }
  }
  