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/*
 * Copyright (C) 2015 Brent Douglas and other contributors
 * as indicated by the @author tags. All rights reserved.
 *
 * 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 io.machinecode.vial.core;

import java.util.Arrays;

/**
 * @author Brent Douglas
 * @since 1.0
 */
public class Util {

  private static final int LINE_SIZE =
      1024; // Integer.decode(System.getProperty("io.machinecode.vial.line.size","1024"));

  /**
   * Fill the specified segment of an array with the provided value. Initializes a small amount of
   * values directly, larger values are them copied using {@link System#arraycopy(Object, int,
   * Object, int, int)} on the previous section in order to make sure the accessed values are in the
   * L1 cache.
   *
   * @param array The array to fill. Must not be null.
   * @param start The first index of the array to be set to value inclusive.
   * @param end The last index of the array to be set to value exclusive.
   * @param value The value to put in the array.
   */
  public static void fill(
      final Object[] array, final int start, final int end, final Object value) {
    assert start >= 0 && start <= end;
    assert end <= array.length;
    assert array.length == 0 || array.length == pow2(array.length);
    final int n = LINE_SIZE;
    int i = Math.min(n, end);
    Arrays.fill(array, start, i, value);
    while (i < end) {
      System.arraycopy(array, i - n, array, i, n);
      i += n;
    }
  }

  /**
   * Compute an acceptable size for the backing array of a hash collection.
   *
   * @param size The amount items required to fit in the array before rehashing. Must be larger than
   *     0.
   * @param factor The load factor of the array.
   * @param max The largest acceptable array size. Must be a power of two.
   * @return The lesser of next power of two greater than or equal to size / factor or max.
   */
  public static int capacity(final int size, final float factor, final int max) {
    assert size > 0;
    int c = (int) Math.ceil(size / factor);
    c--;
    c |= c >> 1;
    c |= c >> 2;
    c |= c >> 4;
    c |= c >> 8;
    c |= c >> 16;
    c++;
    return c >= max ? max : c;
  }

  public static int pow2(int c) {
    assert c > 0;
    c--;
    c |= c >> 1;
    c |= c >> 2;
    c |= c >> 4;
    c |= c >> 8;
    c |= c >> 16;
    c++;
    return c;
  }
}