Class IntervalSize

1
2	/*
3	* Copyright (c) 2016 Vivid Solutions.
4	*
5	* All rights reserved. This program and the accompanying materials
6	* are made available under the terms of the Eclipse Public License 2.0
7	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
8	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
9	* and the Eclipse Distribution License is available at
10	*
11	* http://www.eclipse.org/org/documents/edl-v10.php.
12	*/
13	package org.locationtech.jts.index.quadtree;
14
15	/**
16	* Provides a test for whether an interval is
17	* so small it should be considered as zero for the purposes of
18	* inserting it into a binary tree.
19	* The reason this check is necessary is that round-off error can
20	* cause the algorithm used to subdivide an interval to fail, by
21	* computing a midpoint value which does not lie strictly between the
22	* endpoints.
23	*
24	* @version 1.7
25	*/
26	public class IntervalSize {
27
28	/**
29	* This value is chosen to be a few powers of 2 less than the
30	* number of bits available in the double representation (i.e. 53).
31	* This should allow enough extra precision for simple computations to be correct,
32	* at least for comparison purposes.
33	*/
34	public static final int MIN_BINARY_EXPONENT = -50;
35
36	/**
37	* Computes whether the interval [min, max] is effectively zero width.
38	* I.e. the width of the interval is so much less than the
39	* location of the interval that the midpoint of the interval cannot be
40	* represented precisely.
41	*/
42	public static boolean isZeroWidth(double min, double max)
43	{
44	double width = max - min;
45	if (width == 0.0) return true;
46
47	double maxAbs = Math.max(Math.abs(min), Math.abs(max));
48	double scaledInterval = width / maxAbs;
49	int level = DoubleBits.exponent(scaledInterval);
50	return level <= MIN_BINARY_EXPONENT;
51	}
52	}
53