[H3] Minor optimization in creating Vec2d objects

libs/h3/src/main/java/org/elasticsearch/h3/CoordIJK.java

@@ -111,6 +111,15 @@ public Vec2d ijkToHex2d() {
         return new Vec2d(i - 0.5 * j, j * Constants.M_SQRT3_2);
     }
 
+    /**
+     * Find the center point in spherical coordinates of a hex on a particular icosahedral face.
+     */
+    public LatLng ijkToGeo(int face, int res, boolean substrate) {
+        final int i = Math.subtractExact(this.i, this.k);
+        final int j = Math.subtractExact(this.j, this.k);
+        return Vec2d.hex2dToGeo(i - 0.5 * j, j * Constants.M_SQRT3_2, face, res, substrate);
+    }
+
     /**
      * Add ijk coordinates.
      *
@@ -270,12 +279,10 @@ public void neighbor(int digit) {
      * clockwise aperture 7 grid.
      */
     public void upAp7r() {
-        i = Math.subtractExact(this.i, this.k);
-        j = Math.subtractExact(this.j, this.k);
-        final int i = (int) Math.round((Math.addExact(Math.multiplyExact(2, this.i), this.j)) / 7.0);
-        final int j = (int) Math.round((Math.subtractExact(Math.multiplyExact(3, this.j), this.i)) / 7.0);
-        this.i = i;
-        this.j = j;
+        final int i = Math.subtractExact(this.i, this.k);
+        final int j = Math.subtractExact(this.j, this.k);
+        this.i = (int) Math.round((Math.addExact(Math.multiplyExact(2, i), j)) / 7.0);
+        this.j = (int) Math.round((Math.subtractExact(Math.multiplyExact(3, j), i)) / 7.0);
         this.k = 0;
         ijkNormalize();
     }
@@ -286,12 +293,10 @@ public void upAp7r() {
      *
      */
     public void upAp7() {
-        i = Math.subtractExact(this.i, this.k);
-        j = Math.subtractExact(this.j, this.k);
-        final int i = (int) Math.round((Math.subtractExact(Math.multiplyExact(3, this.i), this.j)) / 7.0);
-        final int j = (int) Math.round((Math.addExact(Math.multiplyExact(2, this.j), this.i)) / 7.0);
-        this.i = i;
-        this.j = j;
+        final int i = Math.subtractExact(this.i, this.k);
+        final int j = Math.subtractExact(this.j, this.k);
+        this.i = (int) Math.round((Math.subtractExact(Math.multiplyExact(3, i), j)) / 7.0);
+        this.j = (int) Math.round((Math.addExact(Math.multiplyExact(2, j), i)) / 7.0);
         this.k = 0;
         ijkNormalize();
     }

libs/h3/src/main/java/org/elasticsearch/h3/FaceIJK.java

@@ -421,8 +421,7 @@ public Overage adjustOverageClassII(int res, boolean pentLeading4, boolean subst
      * @param res The H3 resolution of the cell.
      */
     public LatLng faceIjkToGeo(int res) {
-        Vec2d v = coord.ijkToHex2d();
-        return v.hex2dToGeo(face, res, false);
+        return coord.ijkToGeo(face, res, false);
     }
 
     /**
@@ -526,8 +525,7 @@ public CellBoundary faceIjkPentToCellBoundary(int res, int start, int length) {
             // vert == start + NUM_PENT_VERTS is only used to test for possible
             // intersection on last edge
             if (vert < start + Constants.NUM_PENT_VERTS) {
-                final Vec2d vec = fijk.coord.ijkToHex2d();
-                final LatLng point = vec.hex2dToGeo(fijk.face, adjRes, true);
+                final LatLng point = fijk.coord.ijkToGeo(fijk.face, adjRes, true);
                 boundary.add(point);
             }
             lastFace = fijk.face;
@@ -651,8 +649,7 @@ public CellBoundary faceIjkToCellBoundary(final int res, final int start, final
             // vert == start + NUM_HEX_VERTS is only used to test for possible
             // intersection on last edge
             if (vert < start + Constants.NUM_HEX_VERTS) {
-                final Vec2d vec = fijk.coord.ijkToHex2d();
-                final LatLng point = vec.hex2dToGeo(fijk.face, adjRes, true);
+                final LatLng point = fijk.coord.ijkToGeo(fijk.face, adjRes, true);
                 boundary.add(point);
             }
             lastFace = fijk.face;

libs/h3/src/main/java/org/elasticsearch/h3/Vec2d.java

@@ -96,7 +96,7 @@ final class Vec2d {
     }
 
     /**
-     * Determines the center point in spherical coordinates of a cell given by 2D
+     * Determines the center point in spherical coordinates of a cell given by this 2D
      * hex coordinates on a particular icosahedral face.
      *
      * @param face      The icosahedral face upon which the 2D hex coordinate system is
@@ -106,8 +106,24 @@ final class Vec2d {
      *                  grid relative to the specified resolution.
      */
     public LatLng hex2dToGeo(int face, int res, boolean substrate) {
+        return hex2dToGeo(this.x, this.y, face, res, substrate);
+    }
+
+    /**
+     * Determines the center point in spherical coordinates of a cell given by the provided 2D
+     * hex coordinates on a particular icosahedral face.
+     *
+     * @param x         The x component of the 2D hex coordinates.
+     * @param y         The y component of the 2D hex coordinates.
+     * @param face      The icosahedral face upon which the 2D hex coordinate system is
+     *                  centered.
+     * @param res       The H3 resolution of the cell.
+     * @param substrate Indicates whether or not this grid is actually a substrate
+     *                  grid relative to the specified resolution.
+     */
+    static LatLng hex2dToGeo(double x, double y, int face, int res, boolean substrate) {
         // calculate (r, theta) in hex2d
-        double r = v2dMag();
+        double r = Math.sqrt(x * x + y * y);
 
         if (r < Constants.EPSILON) {
             return faceCenterGeo[face];
@@ -283,15 +299,6 @@ public static Vec2d v2dIntersect(Vec2d p0, Vec2d p1, Vec2d p2, Vec2d p3) {
         return new Vec2d(p0.x + (t * s1x), p0.y + (t * s1y));
     }
 
-    /**
-     * Calculates the magnitude of a 2D cartesian vector.
-     *
-     * @return The magnitude of the vector.
-     */
-    private double v2dMag() {
-        return Math.sqrt(x * x + y * y);
-    }
-
     /**
      * Normalizes radians to a value between 0.0 and two PI.
      *