Optimization in getEdgeHexagons (#913)

* Optimization in getEdgeHexagons

Replace 4 fpdiv's with 1 fpdiv and 4 fpmul's

* Updated changelog to add #913

CHANGELOG.md

@@ -9,7 +9,7 @@ The public API of this library consists of the functions declared in file
 ### Changed
 - Replace internal algorithm for `polygonToCells` with a new version that is more memory-efficient (#785)
 - Reorganize tests into public / internal. (#762)
-- Performance enhancement for aarch64, may improve other platforms (#790, #792, #852, #905)
+- Performance enhancement for aarch64, may improve other platforms (#790, #792, #852, #905, #913)
 - `clang-format` upgraded to version 14. (#834)
 - Fixed tests that incorrectly did not test resolution 15. (#820)
 - Use `CMAKE_INSTALL_LIBDIR` when choosing where to install library files. (#819)

src/h3lib/lib/algos.c

@@ -837,12 +837,13 @@ H3Error _getEdgeHexagons(const GeoLoop *geoloop, int64_t numHexagons, int res,
         }
         for (int64_t j = 0; j < numHexesEstimate; j++) {
             LatLng interpolate;
+            double invNumHexesEst = 1.0 / numHexesEstimate;
             interpolate.lat =
-                (origin.lat * (numHexesEstimate - j) / numHexesEstimate) +
-                (destination.lat * j / numHexesEstimate);
+                (origin.lat * (numHexesEstimate - j) * invNumHexesEst) +
+                (destination.lat * j * invNumHexesEst);
             interpolate.lng =
-                (origin.lng * (numHexesEstimate - j) / numHexesEstimate) +
-                (destination.lng * j / numHexesEstimate);
+                (origin.lng * (numHexesEstimate - j) * invNumHexesEst) +
+                (destination.lng * j * invNumHexesEst);
             H3Index pointHex;
             H3Error e = H3_EXPORT(latLngToCell)(&interpolate, res, &pointHex);
             if (e) {