add fuzzer for cellsToMultiPolygon (#1122)

Author: isaacbrodsky

CMakeLists.txt

@@ -295,6 +295,7 @@ set(OTHER_SOURCE_FILES
     src/apps/fuzzers/fuzzerLatLngToCell.c
     src/apps/fuzzers/fuzzerCellToLatLng.c
     src/apps/fuzzers/fuzzerGridDisk.c
+    src/apps/fuzzers/fuzzerCellsToMultiPolygon.c
     src/apps/fuzzers/fuzzerCellsToLinkedMultiPolygon.c
     src/apps/fuzzers/fuzzerDistances.c
     src/apps/fuzzers/fuzzerCellArea.c
@@ -622,6 +623,8 @@ if(BUILD_FUZZERS)
     add_h3_fuzzer(fuzzerLatLngToCell src/apps/fuzzers/fuzzerLatLngToCell.c)
     add_h3_fuzzer(fuzzerCellToLatLng src/apps/fuzzers/fuzzerCellToLatLng.c)
     add_h3_fuzzer(fuzzerGridDisk src/apps/fuzzers/fuzzerGridDisk.c)
+    add_h3_fuzzer(fuzzerCellsToMultiPolygon
+                  src/apps/fuzzers/fuzzerCellsToMultiPolygon.c)
     add_h3_fuzzer(fuzzerCellsToLinkedMultiPolygon
                   src/apps/fuzzers/fuzzerCellsToLinkedMultiPolygon.c)
     add_h3_fuzzer(fuzzerDistances src/apps/fuzzers/fuzzerDistances.c)

src/apps/fuzzers/README.md

@@ -24,6 +24,8 @@ The public API of H3 is covered in the following fuzzers:
 | cellToParent | [fuzzerHierarchy](./fuzzerHierarchy.c)
 | cellToVertex | [fuzzerVertexes](./fuzzerVertexes.c)
 | cellToVertexes | [fuzzerVertexes](./fuzzerVertexes.c)
+| cellsToMultiPolygon | [fuzzerCellsToMultiPolygon.c](./fuzzerCellsToMultiPolygon.c)
+| cellsToLinkedMultiPolygon | [fuzzerCellsToLinkedMultiPolygon.c](./fuzzerCellsToLinkedMultiPolygon.c)
 | cellsToDirectedEdge | [fuzzerDirectedEdge](./fuzzerDirectedEdge.c)
 | childPosToCell| [fuzzerCellToChildPos](./fuzzerCellToChildPos.c)
 | compactCells | [fuzzerCompact](./fuzzerCompact.c)

src/apps/fuzzers/fuzzerCellsToMultiPolygon.c

@@ -0,0 +1,37 @@
+/*
+ * 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.
+ */
+/** @file
+ * @brief Fuzzer program for cellsToMultiPolygon
+ */
+
+#include "aflHarness.h"
+#include "h3api.h"
+#include "utility.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+    const H3Index *h3Set = (const H3Index *)data;
+    int sz = size / sizeof(H3Index);
+
+    GeoMultiPolygon polygon;
+    H3Error err = H3_EXPORT(cellsToMultiPolygon)(h3Set, sz, &polygon);
+
+    if (!err) {
+        H3_EXPORT(destroyGeoMultiPolygon)(&polygon);
+    }
+    return 0;
+}
+
+AFL_HARNESS_MAIN(sizeof(H3Index) * 1024);