/*
* 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 v1.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.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;
}
}