1 files changed, 63 insertions, 0 deletions
diff --git a/externals/dynarmic/tests/fp/mantissa_util_tests.cpp b/externals/dynarmic/tests/fp/mantissa_util_tests.cpp
new file mode 100644
index 0000000000..cff942c73f
--- /dev/null
+++ b/externals/dynarmic/tests/fp/mantissa_util_tests.cpp
@@ -0,0 +1,63 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2018 MerryMage
+ * SPDX-License-Identifier: 0BSD
+ */
+
+#include <tuple>
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+#include <mcl/stdint.hpp>
+
+#include "../rand_int.h"
+#include "dynarmic/common/fp/mantissa_util.h"
+#include "dynarmic/common/safe_ops.h"
+
+using namespace Dynarmic;
+using namespace Dynarmic::FP;
+
+TEST_CASE("ResidualErrorOnRightShift", "[fp]") {
+    const std::vector<std::tuple<u32, int, ResidualError>> test_cases{
+        {0x00000001, 1, ResidualError::Half},
+        {0x00000002, 1, ResidualError::Zero},
+        {0x00000001, 2, ResidualError::LessThanHalf},
+        {0x00000002, 2, ResidualError::Half},
+        {0x00000003, 2, ResidualError::GreaterThanHalf},
+        {0x00000004, 2, ResidualError::Zero},
+        {0x00000005, 2, ResidualError::LessThanHalf},
+        {0x00000006, 2, ResidualError::Half},
+        {0x00000007, 2, ResidualError::GreaterThanHalf},
+    };
+
+    for (auto [mantissa, shift, expected_result] : test_cases) {
+        const ResidualError result = ResidualErrorOnRightShift(mantissa, shift);
+        REQUIRE(result == expected_result);
+    }
+}
+
+TEST_CASE("ResidualErrorOnRightShift Randomized", "[fp]") {
+    for (size_t test = 0; test < 100000; test++) {
+        const u64 mantissa = mcl::bit::sign_extend<32, u64>(RandInt<u32>(0, 0xFFFFFFFF));
+        const int shift = RandInt<int>(-60, 60);
+
+        const ResidualError result = ResidualErrorOnRightShift(mantissa, shift);
+
+        const u64 calculated_error = Safe::ArithmeticShiftRightDouble(mantissa, u64(0), shift);
+        const ResidualError expected_result = [&] {
+            constexpr u64 half_error = 0x8000'0000'0000'0000ull;
+            if (calculated_error == 0) {
+                return ResidualError::Zero;
+            }
+            if (calculated_error < half_error) {
+                return ResidualError::LessThanHalf;
+            }
+            if (calculated_error == half_error) {
+                return ResidualError::Half;
+            }
+            return ResidualError::GreaterThanHalf;
+        }();
+
+        INFO(std::hex << "mantissa " << mantissa << " shift " << shift << " calculated_error " << calculated_error);
+        REQUIRE(result == expected_result);
+    }
+}