Fix root-node precision problems

tzaeschke · Jun 30, 2024 · 97d1f45 · 97d1f45
1 parent f55e4b8
commit 97d1f45
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Showing 3 changed files with 50 additions and 3 deletions.
diff --git a/src/main/java/org/tinspin/index/qthypercube2/QuadTreeKD2.java b/src/main/java/org/tinspin/index/qthypercube2/QuadTreeKD2.java
@@ -132,7 +132,7 @@ private void adjustRootSize(double[] key) {
 			for (int i = 0; i < root.getValueCount(); i++) {
 				dMax = Math.max(dMax, MathTools.maxDelta(root.getValues()[i].point(), root.getCenter()));
 			}
-			double radius = MathTools.floorPowerOfTwo(dMax) * 2;
+			double radius = MathTools.ceilPowerOfTwo(dMax + QUtil.EPS_MUL);
 			if (radius > 0) {
 				root.adjustRadius(radius);
 			} else if (root.getValueCount() >= maxNodeSize - 1) {

diff --git a/src/main/java/org/tinspin/index/util/MathTools.java b/src/main/java/org/tinspin/index/util/MathTools.java
@@ -21,11 +21,23 @@ public class MathTools {
 
     private MathTools() {}
 
+    /**
+     * Similar to Math.ceil() with the ceiling being the next higher power of 2.
+     * The resulting number can repeatedly and (almost) always be divided by two without loss of precision.
+     * @param d input
+     * @return next power of two above or equal to 'input'
+     */
+    public static double ceilPowerOfTwo(double d) {
+        double ceil = floorPowerOfTwo(d);
+        return ceil == d ? ceil : ceil * 2;
+    }
+
     /**
      * Similar to Math.floor() with the floor being the next lower power of 2.
-     * The resulting number can repeatedly (almost) always be divided by two without loss of precision.
+     * The resulting number can repeatedly and (almost) always be divided by two without loss of precision.
+     * We calculate the "floor" by setting the "fraction" of the bit representation to 0.
      * @param d input
-     * @return next lower power of two below 'input'
+     * @return next power of two below or equal to 'input'
      */
     public static double floorPowerOfTwo(double d) {
         // Set fraction to "0".

diff --git a/src/test/java/org/tinspin/util/MathToolsTest.java b/src/test/java/org/tinspin/util/MathToolsTest.java
@@ -25,13 +25,48 @@
 
 public class MathToolsTest {
 
+    @Test
+    public void powerOfTwoCeil() {
+        assertEquals(1./32., MathTools.ceilPowerOfTwo(0.03), 0.0);
+        assertEquals(0.5, MathTools.ceilPowerOfTwo(0.3), 0.0);
+        assertEquals(4, MathTools.ceilPowerOfTwo(3), 0.0);
+        assertEquals(32, MathTools.ceilPowerOfTwo(30), 0.0);
+        assertEquals(512, MathTools.ceilPowerOfTwo(300), 0.0);
+
+        assertEquals(-0.5, MathTools.ceilPowerOfTwo(-0.3), 0.0);
+        assertEquals(-4, MathTools.ceilPowerOfTwo(-3), 0.0);
+        assertEquals(-32, MathTools.ceilPowerOfTwo(-30), 0.0);
+
+        // identity
+        assertEquals(0, MathTools.ceilPowerOfTwo(0), 0.0);
+        assertEquals(-0.5, MathTools.ceilPowerOfTwo(-0.5), 0.0);
+        assertEquals(0.5, MathTools.ceilPowerOfTwo(0.5), 0.0);
+        assertEquals(-1, MathTools.ceilPowerOfTwo(-1), 0.0);
+        assertEquals(1, MathTools.ceilPowerOfTwo(1), 0.0);
+        assertEquals(-2, MathTools.ceilPowerOfTwo(-2), 0.0);
+        assertEquals(2, MathTools.ceilPowerOfTwo(2), 0.0);
+    }
+
     @Test
     public void powerOfTwoFloor() {
         assertEquals(1./64., MathTools.floorPowerOfTwo(0.03), 0.0);
         assertEquals(0.25, MathTools.floorPowerOfTwo(0.3), 0.0);
         assertEquals(2, MathTools.floorPowerOfTwo(3), 0.0);
         assertEquals(16, MathTools.floorPowerOfTwo(30), 0.0);
         assertEquals(256, MathTools.floorPowerOfTwo(300), 0.0);
+
+        assertEquals(-0.25, MathTools.floorPowerOfTwo(-0.3), 0.0);
+        assertEquals(-2, MathTools.floorPowerOfTwo(-3), 0.0);
+        assertEquals(-16, MathTools.floorPowerOfTwo(-30), 0.0);
+
+        // identity
+        assertEquals(0, MathTools.ceilPowerOfTwo(0), 0.0);
+        assertEquals(-0.5, MathTools.ceilPowerOfTwo(-0.5), 0.0);
+        assertEquals(0.5, MathTools.ceilPowerOfTwo(0.5), 0.0);
+        assertEquals(-1, MathTools.ceilPowerOfTwo(-1), 0.0);
+        assertEquals(1, MathTools.ceilPowerOfTwo(1), 0.0);
+        assertEquals(-2, MathTools.ceilPowerOfTwo(-2), 0.0);
+        assertEquals(2, MathTools.ceilPowerOfTwo(2), 0.0);
     }
 
     @Test