Had to reimplement getValue to not use TreeMap/SortedMap apis unavailable in Froyo. Added some comments so it should be easier to read. Test cases continue to pass.

core/src/net/sf/openrocket/util/LinearInterpolator.java

@@ -1,7 +1,7 @@
 package net.sf.openrocket.util;
 
 import java.util.Iterator;
-import java.util.Map;
+import java.util.SortedMap;
 import java.util.TreeMap;
 
 public class LinearInterpolator implements Cloneable {
@@ -14,7 +14,7 @@ public class LinearInterpolator implements Cloneable {
 	 */
 	public LinearInterpolator() {
 	}
-	
+
 	/**
 	 * Construct a <code>LinearInterpolator</code> with the given points.
 	 * 
@@ -27,8 +27,8 @@ public class LinearInterpolator implements Cloneable {
 	public LinearInterpolator(double[] x, double[] y) {
 		addPoints(x,y);
 	}
-	
+
-	
+
 	/**
 	 * Add the point to the linear interpolation.
 	 * 
@@ -38,7 +38,7 @@ public class LinearInterpolator implements Cloneable {
 	public void addPoint(double x, double y) {
 		sortMap.put(x, y);
 	}
-	
+
 	/**
 	 * Add the points to the linear interpolation.
 	 * 
@@ -56,41 +56,66 @@ public class LinearInterpolator implements Cloneable {
 			sortMap.put(x[i],y[i]);
 		}
 	}
-	
-	
-	
-	public double getValue(double x) {
-		Map.Entry<Double,Double> e1, e2;
-		double x1, x2;
-		double y1, y2;
-		
-		e1 = sortMap.floorEntry(x);
-		
-		if (e1 == null) {
-			// x smaller than any value in the set
-			e1 = sortMap.firstEntry();
-			if (e1 == null) {
-				throw new IllegalStateException("No points added yet to the interpolator.");
-			}
-			return e1.getValue();
-		}
-		
-		x1 = e1.getKey();
-		e2 = sortMap.higherEntry(x1);
 
-		if (e2 == null) {
+
-			// x larger than any value in the set
+
-			return e1.getValue();
+	public double getValue(double x) {
+		double x1, x2;
+		Double y1, y2;
+		// Froyo does not support floorEntry, firstEntry or higherEntry.  We instead have to
+		// resort to using other more awkward methods.
+
+		y1 = sortMap.get(x);
+
+		if ( y1 != null ) {
+			// Wow, x was a key in the map.  Such luck.
+			return y1.doubleValue();
+		}
+
+		// we now know that x is not in the map, so we need to find the lower and higher keys.
+		
+		// let's just make certain that our map is not empty.
+		if ( sortMap.isEmpty() ) {
+			throw new IllegalStateException("No points added yet to the interpolator.");
 		}
 		
-		x2 = e2.getKey();
+		// firstKey in the map - cannot be null since the map is not empty.
-		y1 = e1.getValue();
+		Double firstKey = sortMap.firstKey();
-		y2 = e2.getValue();
+
+		// x is smaller than the first entry in the map.
+		if ( x < firstKey.doubleValue() ) {
+			y1 = sortMap.get(firstKey);
+			return y1.doubleValue();
+		}
 		
+		// floor key is the largest key smaller than x - since we have at least one key,
+		// and x>=firstKey, we know that floorKey != null.
+		Double floorKey = sortMap.subMap(firstKey, x).lastKey();
+
+		x1 = floorKey.doubleValue();
+		y1 = sortMap.get(floorKey);
+
+		// Now we need to find the key that is greater or equal to x
+		SortedMap<Double,Double> tailMap = sortMap.tailMap(x);
+
+		// Check if x is bigger than all the entries.
+		if ( tailMap.isEmpty() ) {
+			return y1.doubleValue();
+		}
+		Double ceilKey = tailMap.firstKey();
+		
+		// Check if x is bigger than all the entries.
+		if ( ceilKey == null ) {
+			return y1.doubleValue();
+		}
+		
+		x2 = ceilKey.doubleValue();
+		y2 = sortMap.get(ceilKey);
+
 		return (x - x1)/(x2-x1) * (y2-y1) + y1;
 	}
-	
+
-	
+
 	public double[] getXPoints() {
 		double[] x = new double[sortMap.size()];
 		Iterator<Double> iter = sortMap.keySet().iterator();
@@ -99,8 +124,8 @@ public class LinearInterpolator implements Cloneable {
 		}
 		return x;
 	}
-	
+
-	
+
 	@SuppressWarnings("unchecked")
 	@Override
 	public LinearInterpolator clone() {