/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2001-2006 Vivid Solutions
* (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*/
package org.geotools.geometry.iso.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.
*
*
*
* @source $URL$
* @version 1.7.2
*/
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;
}
}