[MISC] Add HIBF_UNREACHABLE

Author: eseiler

.github/workflows/ci_coverage.yml

@@ -78,6 +78,7 @@ jobs:
                 --exclude ${GITHUB_WORKSPACE}/test/include/hibf/test/iterator_test_template.hpp \
                 --exclude-lines-by-pattern '^\s*$' \
                 --exclude-lines-by-pattern '^\s*};$' \
+                --exclude-lines-by-pattern '^\s*HIBF_UNREACHABLE;' \
                 --exclude-unreachable-branches \
                 --exclude-throw-branches \
                 --exclude-noncode-lines \

include/hibf/platform.hpp

@@ -101,6 +101,24 @@
 #    error "This is not a C++ compiler."
 #endif
 
+/*!\brief Macro to mark unreachable code paths.
+ * \details
+ * In debug mode, it triggers an assertion failure.
+ * In release mode, it calls `std::unreachable`.
+ * ### Example
+ * \include test/snippet/platform_unreachable.cpp
+ */
+#ifndef HIBF_UNREACHABLE
+// The do { ... } while (0) is a common pattern to enforce the semicolon after the macro.
+// clang-format off
+#    ifndef NDEBUG
+#        define HIBF_UNREACHABLE do { assert(false); } while (0) // GCOVR_EXCL_LINE
+#    else
+#        define HIBF_UNREACHABLE do { std::unreachable(); } while (0)
+#    endif
+#endif
+// clang-format on
+
 // ============================================================================
 //  Dependencies
 // ============================================================================

src/interleaved_bloom_filter.cpp

@@ -210,16 +210,11 @@ interleaved_bloom_filter::membership_agent_type::bulk_contains(size_t const valu
     size_t const bin_words_ = ibf_ptr->bin_words;
     size_t const hash_funs_ = ibf_ptr->hash_funs;
 
-#ifndef NDEBUG
-    assert(bin_words_ != 0u);
-    assert(hash_funs_ != 0u);
-#else
     // Removes case for bin_words_ == 0u. The same statment inside the switch-case wouldn't have that effect.
     if (bin_words_ == 0u)
-        __builtin_unreachable();
+        HIBF_UNREACHABLE;
     if (hash_funs_ == 0u)
-        __builtin_unreachable();
-#endif
+        HIBF_UNREACHABLE;
 
     for (size_t i = 0; i < hash_funs_; ++i)
         bloom_filter_indices[i] = ibf_ptr->hash_and_fit(value, ibf_ptr->hash_seeds[i]) / 64u;

test/snippet/platform_unreachable.cpp

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2006-2025, Knut Reinert & Freie Universität Berlin
+// SPDX-FileCopyrightText: 2016-2025, Knut Reinert & MPI für molekulare Genetik
+// SPDX-License-Identifier: CC0-1.0
+
+#include <utility> // for unreachable
+
+#include <hibf/platform.hpp> // for HIBF_UNREACHABLE
+
+int foo(int const i)
+{
+    // The compiler will not generate the default branch.
+    // Note that an input of any `i` other than `0` and `1` is undefined behavior!
+    switch (i)
+    {
+    case 0:
+        return -5;
+    case 1:
+        return 3;
+    default:
+        HIBF_UNREACHABLE; // HIBF_UNREACHABLE must be followed by a semicolon.
+    }
+}