Add Gosper island boundary edge iterator

CMakeLists.txt

@@ -187,6 +187,7 @@ set(LIB_SOURCE_FILES
     src/h3lib/lib/localij.c
     src/h3lib/lib/latLng.c
     src/h3lib/lib/directedEdge.c
+    src/h3lib/lib/iterGosper.c
     src/h3lib/lib/mathExtensions.c
     src/h3lib/lib/iterators.c
     src/h3lib/lib/vertexGraph.c
@@ -286,6 +287,7 @@ set(OTHER_SOURCE_FILES
     src/apps/testapps/testH3IteratorsInternal.c
     src/apps/testapps/testMathExtensionsInternal.c
     src/apps/testapps/testDescribeH3Error.c
+    src/apps/testapps/testGosperIter.c
     src/apps/testapps/testGeoLoopArea.c
     src/apps/miscapps/cellToBoundaryHier.c
     src/apps/miscapps/cellToLatLngHier.c
@@ -325,6 +327,7 @@ set(OTHER_SOURCE_FILES
     src/apps/benchmarks/benchmarkGridDiskCells.c
     src/apps/benchmarks/benchmarkGridPathCells.c
     src/apps/benchmarks/benchmarkDirectedEdge.c
+    src/apps/benchmarks/benchmarkGosperIter.c
     src/apps/benchmarks/benchmarkVertex.c
     src/apps/benchmarks/benchmarkIsValidCell.c
     src/apps/benchmarks/benchmarkH3Api.c
@@ -674,6 +677,8 @@ if(BUILD_BENCHMARKS)
                      src/apps/benchmarks/benchmarkGridPathCells.c)
     add_h3_benchmark(benchmarkDirectedEdge
                      src/apps/benchmarks/benchmarkDirectedEdge.c)
+    add_h3_benchmark(benchmarkGosperIter
+                     src/apps/benchmarks/benchmarkGosperIter.c)
     add_h3_benchmark(benchmarkVertex src/apps/benchmarks/benchmarkVertex.c)
     add_h3_benchmark(benchmarkIsValidCell
                      src/apps/benchmarks/benchmarkIsValidCell.c)

CMakeTests.cmake

@@ -262,6 +262,7 @@ add_h3_test(testH3IteratorsInternal src/apps/testapps/testH3IteratorsInternal.c)
 add_h3_test(testMathExtensionsInternal
             src/apps/testapps/testMathExtensionsInternal.c)
 add_h3_test(testDescribeH3Error src/apps/testapps/testDescribeH3Error.c)
+add_h3_test(testGosperIter src/apps/testapps/testGosperIter.c)
 add_h3_test(testGeoLoopArea src/apps/testapps/testGeoLoopArea.c)
 
 add_h3_test_with_arg(testH3NeighborRotations

src/apps/benchmarks/benchmarkGosperIter.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2026 Uber Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "benchmark.h"
+#include "iterators.h"
+
+H3Index hex2 = 0x820887fffffffff;   // res 2 hexagon
+H3Index pent2 = 0x820807fffffffff;  // res 2 pentagon
+
+void exhaustGosper(H3Index cell, int childRes) {
+    IterEdgesGosper iter = iterInitGosper(cell, childRes);
+    while (iter.e) iterStepGosper(&iter);
+}
+
+BEGIN_BENCHMARKS();
+
+// res: 2 -> 2
+BENCHMARK(hex_plus0, 50000000, { exhaustGosper(hex2, 2); });
+BENCHMARK(pent_plus0, 50000000, { exhaustGosper(pent2, 2); });
+
+// res: 2 -> 3
+BENCHMARK(hex_plus1, 500000, { exhaustGosper(hex2, 3); });
+BENCHMARK(pent_plus1, 500000, { exhaustGosper(pent2, 3); });
+
+// res: 2 -> 4
+BENCHMARK(hex_plus2, 100000, { exhaustGosper(hex2, 4); });
+BENCHMARK(pent_plus2, 100000, { exhaustGosper(pent2, 4); });
+
+// res: 2 -> 7
+BENCHMARK(hex_plus5, 1000, { exhaustGosper(hex2, 7); });
+BENCHMARK(pent_plus5, 1000, { exhaustGosper(pent2, 7); });
+
+// res: 2 -> 10
+BENCHMARK(hex_plus8, 100, { exhaustGosper(hex2, 10); });
+BENCHMARK(pent_plus8, 100, { exhaustGosper(pent2, 10); });
+
+// res: 2 -> 13
+BENCHMARK(hex_plus11, 10, { exhaustGosper(hex2, 13); });
+BENCHMARK(pent_plus11, 10, { exhaustGosper(pent2, 13); });
+
+END_BENCHMARKS();