From 7335c8e1d881db0dd4a2937d9e55d01ad98a930e Mon Sep 17 00:00:00 2001
From: Greg Burd <greg@burd.me>
Date: Thu, 13 Jun 2024 05:58:12 -0400
Subject: [PATCH] find a span of unset bits in an empty map

---
 CMakeLists.txt  | 9 ++++++++-
 Makefile        | 6 ++++++
 src/sparsemap.c | 7 +++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 088bb31..3dc0c4a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,4 +84,11 @@ add_executable(soak tests/soak.c lib/common.c lib/tdigest.c lib/roaring.c)
 target_link_libraries(soak PRIVATE sparsemap)
 target_include_directories(soak PRIVATE ${HEADER_DIR} lib)
 target_link_libraries(soak PUBLIC m)
-add_custom_target(run_soak COMMAND soak WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
\ No newline at end of file
+add_custom_target(run_soak COMMAND soak WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+
+# Add fuzzer program
+add_executable(fuzzer tests/fuzzer.c)
+target_link_libraries(fuzzer PRIVATE sparsemap)
+target_include_directories(fuzzer PRIVATE ${HEADER_DIR} lib)
+target_link_libraries(fuzzer PUBLIC m)
+add_custom_target(run_fuzzer COMMAND fuzzer WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
diff --git a/Makefile b/Makefile
index 2c00376..1623914 100644
--- a/Makefile
+++ b/Makefile
@@ -49,6 +49,9 @@ test: tests
 soak: tests
 	env ASAN_OPTIONS=detect_leaks=1 LSAN_OPTIONS=verbosity=1:log_threads=1 ./tests/soak
 
+fuzzer: tests
+	env ASAN_OPTIONS=detect_leaks=1 LSAN_OPTIONS=verbosity=1:log_threads=1 ./tests/fuzzer ./crash.case
+
 tests/test: $(TEST_OBJS) $(LIB_OBJS) $(STATIC_LIB)
 	$(CC) $^ $(LIBS) -o $@ $(TEST_FLAGS)
 
@@ -90,6 +93,9 @@ examples/ex_4: $(LIB_OBJS) examples/ex_4.o $(STATIC_LIB)
 tests/soak: $(LIB_OBJS) tests/soak.o $(STATIC_LIB)
 	$(CC) $^ $(LIBS) -o $@ $(TEST_FLAGS)
 
+tests/fuzzer: $(LIB_OBJS) tests/fuzzer.o $(STATIC_LIB)
+	$(CC) $^ $(LIBS) -o $@ $(TEST_FLAGS) -DFUZZ_DEBUG
+
 todo:
 	rg -i 'todo|gsb|abort'
 
diff --git a/src/sparsemap.c b/src/sparsemap.c
index da9ad78..4b1d479 100644
--- a/src/sparsemap.c
+++ b/src/sparsemap.c
@@ -1705,6 +1705,10 @@ sparsemap_select(sparsemap_t *map, sparsemap_idx_t n, bool value)
   sm_idx_t start;
   size_t count = __sm_get_chunk_count(map);
 
+  if (count == 0 && value == false) {
+    return n;
+  }
+
   uint8_t *p = __sm_get_chunk_data(map, 0);
 
   for (size_t i = 0; i < count; i++) {
@@ -1847,6 +1851,9 @@ sparsemap_span(sparsemap_t *map, sparsemap_idx_t idx, size_t len, bool value)
      many selects we can avoid by taking the rank of the range and starting
      at that bit. */
   nth = (idx == 0) ? 0 : sparsemap_rank(map, 0, idx - 1, value);
+  if (SPARSEMAP_NOT_FOUND(nth)) {
+    return nth;
+  }
   /* Find the first bit that matches value, then... */
   offset = sparsemap_select(map, nth, value);
   do {