
/*
 * Copyright (c) 2016 Vivid Solutions.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *
 * http://www.eclipse.org/org/documents/edl-v10.php.
 */
package org.locationtech.jts.index.quadtree;

/**
 * Provides a test for whether an interval is
 * so small it should be considered as zero for the purposes of
 * inserting it into a binary tree.
 * The reason this check is necessary is that round-off error can
 * cause the algorithm used to subdivide an interval to fail, by
 * computing a midpoint value which does not lie strictly between the
 * endpoints.
 *
 * @version 1.7
 */
public class IntervalSize {

  /**
   * This value is chosen to be a few powers of 2 less than the
   * number of bits available in the double representation (i.e. 53).
   * This should allow enough extra precision for simple computations to be correct,
   * at least for comparison purposes.
   */
  public static final int MIN_BINARY_EXPONENT = -50;

  /**
   * Computes whether the interval [min, max] is effectively zero width.
   * I.e. the width of the interval is so much less than the
   * location of the interval that the midpoint of the interval cannot be
   * represented precisely.
   */
  public static boolean isZeroWidth(double min, double max)
  {
    double width = max - min;
    if (width == 0.0) return true;

    double maxAbs = Math.max(Math.abs(min), Math.abs(max));
    double scaledInterval = width / maxAbs;
    int level = DoubleBits.exponent(scaledInterval);
    return level <= MIN_BINARY_EXPONENT;
  }
}
