Fix non-atomic refcount decrement

include/roaring/portability.h

@@ -635,7 +635,7 @@ static inline void croaring_refcount_inc(croaring_refcount_t *val) {
 static inline bool croaring_refcount_dec(croaring_refcount_t *val) {
     assert(*val > 0);
     *val -= 1;
-    return val == 0;
+    return *val == 0;
 }
 
 static inline uint32_t croaring_refcount_get(const croaring_refcount_t *val) {

tests/CMakeLists.txt

@@ -18,6 +18,9 @@ add_c_test(run_container_unit)
 add_c_test(toplevel_unit)
 add_c_test(util_unit)
 add_c_test(format_portability_unit)
+add_c_test(refcount_unit)
+target_compile_definitions(refcount_unit PRIVATE
+  CROARING_ATOMIC_IMPL=CROARING_ATOMIC_IMPL_NONE)
 add_c_test(robust_deserialization_unit)
 add_c_test(container_comparison_unit)
 add_c_test(add_offset)

tests/refcount_unit.c

@@ -0,0 +1,21 @@
+#include <stdint.h>
+
+#include <roaring/portability.h>
+
+#include "test.h"
+
+DEFINE_TEST(test_non_atomic_refcount) {
+    croaring_refcount_t refcount = 2;
+
+    assert_false(croaring_refcount_dec(&refcount));
+    assert_int_equal(croaring_refcount_get(&refcount), 1);
+    assert_true(croaring_refcount_dec(&refcount));
+    assert_int_equal(croaring_refcount_get(&refcount), 0);
+}
+
+int main() {
+    const struct CMUnitTest tests[] = {
+        cmocka_unit_test(test_non_atomic_refcount),
+    };
+    return cmocka_run_group_tests(tests, NULL, NULL);
+}