refactor: mul_hi64() fallback implementation now compiles on all platforms

Author: benthevining

libbenbot/src/search/Search.cpp

@@ -467,7 +467,6 @@ void Context::search() // NOLINT(readability-function-cognitive-complexity)
     transTable.new_search();
     callbacks.search_start(options);
 
-    // TODO: use a separate MoveList
     // if the movesToSearch was empty, then we search all legal moves
     if (options.movesToSearch.empty()) {
         chess::moves::generate(position, std::back_inserter(options.movesToSearch));

libutil/src/MulHi64.cpp

@@ -12,11 +12,37 @@
  * ======================================================================================
  */
 
+#include <cstdint>
 #include <libutil/Math.hpp>
 
-#ifdef __SIZEOF_INT128__
+namespace {
+[[nodiscard, gnu::const, maybe_unused]] auto mul_hi64_fallback(
+    const uint64_t first, const uint64_t second) noexcept
+    -> uint64_t
+{
+    auto get_lo_32_bits = [](const uint64_t value) noexcept {
+        return static_cast<uint64_t>(static_cast<std::uint32_t>(value));
+    };
+
+    auto get_hi_32_bits = [](const uint64_t value) noexcept {
+        return static_cast<uint64_t>(value >> UINT64_C(32));
+    };
+
+    const auto a_lo = get_lo_32_bits(first);
+    const auto a_hi = get_hi_32_bits(first);
+
+    const auto b_lo = get_lo_32_bits(second);
+    const auto b_hi = get_hi_32_bits(second);
+
+    const auto c_1 = get_hi_32_bits(a_lo * b_lo);
+    const auto c_2 = (a_hi * b_lo) + c_1;
+    const auto c_3 = (a_lo * b_hi) + get_lo_32_bits(c_2);
 
-#    include <cstdint>
+    return (a_hi * b_hi) + get_hi_32_bits(c_2) + get_hi_32_bits(c_3);
+}
+} // namespace
+
+#ifdef __SIZEOF_INT128__
 
 namespace util::math {
 
@@ -67,9 +93,6 @@ auto mul_hi64(
 } // namespace util::math
 
 #else
-
-#    include <cstdint>
-
 #    warning "No optimized version of mul_hi64() is available, using fallback"
 
 namespace util::math {
@@ -78,21 +101,7 @@ auto mul_hi64(
     const uint64_t first, const uint64_t second) noexcept
     -> uint64_t
 {
-    auto get_lo_32_bits = [](const uint64_t value) {
-        return static_cast<uint64_t>(static_cast<std::uint32_t>(value));
-    };
-
-    const auto a_lo = get_lo_32_bits(first);
-    const auto a_hi = first >> 32uz;
-
-    const auto b_lo = get_lo_32_bits(second);
-    const auto b_hi = second >> 32uz;
-
-    const auto c_1 = (a_lo * b_lo) >> 32uz;
-    const auto c_2 = (a_hi * b_lo) + c_1;
-    const auto c_3 = (a_lo * b_hi) + get_lo_32_bits(c_2);
-
-    return (a_hi * b_hi) + (c_2 >> 32uz) + (c_3 >> 32uz);
+    return mul_hi64_fallback(first, second);
 }
 
 } // namespace util::math