content: /*
   * Copyright (C) 2007 The Guava Authors
   *
   * 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
   *
   * 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.weex.utils;
  
  import java.util.HashMap;
  
  public class WXDataStructureUtil {
  
    /**
     * The largest power of two that can be represented as an {@code int}.
     */
    private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
  
    /**
     * Creates a {@code HashMap} instance, with a high enough "initial capacity" that it <i>should</i>
     * hold {@code expectedSize} elements without growth. This behavior cannot be broadly guaranteed,
     * but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed that the method
     * isn't inadvertently <i>oversizing</i> the returned map.
     *
     * @param expectedSize the number of entries you expect to add to the returned map
     * @return a new, empty {@code HashMap} with enough capacity to hold {@code expectedSize} entries
     * without resizing
     * @throws IllegalArgumentException if {@code expectedSize} is negative
     */
    public static <K, V> HashMap<K, V> newHashMapWithExpectedSize(int expectedSize) {
      return new HashMap<>(capacity(expectedSize));
    }
  
    /**
     * Returns a capacity that is sufficient to keep the map from being resized as long as it grows no
     * larger than expectedSize and the load factor is >= its default (0.75).
     */
    private static int capacity(int expectedSize) {
      if (expectedSize < 3) {
        checkNonnegative(expectedSize, "expectedSize");
        return expectedSize + 1;
      }
      if (expectedSize < MAX_POWER_OF_TWO) {
        // This is the calculation used in JDK8 to resize when a putAll
        // happens; it seems to be the most conservative calculation we
        // can make.  0.75 is the default load factor.
        return (int) ((float) expectedSize / 0.75F + 1.0F);
      }
      return Integer.MAX_VALUE; // any large value
    }
  
    private static int checkNonnegative(int value, String name) {
      if (value < 0) {
        throw new IllegalArgumentException(name + " cannot be negative but was: " + value);
      }
      return value;
    }
  }
  