JitCommon: Signed 32-bit division magic constants

Add a function to calculate the magic constants required to optimize
signed 32-bit division.

Since this optimization is not exclusive to any particular architecture,
JitCommon seemed like a good place to put this.

1 files changed, 33 insertions, 0 deletions

diff --git a/Source/UnitTests/DivUtilsTest.cpp b/Source/UnitTests/DivUtilsTest.cpp
new file mode 100644
index 0000000000..7802fc8496
--- /dev/null
+++ b/Source/UnitTests/DivUtilsTest.cpp
@@ -0,0 +1,33 @@
+// Copyright 2021 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include <gtest/gtest.h>
+
+#include "Core/PowerPC/JitCommon/DivUtils.h"
+
+using namespace JitCommon;
+
+TEST(DivUtils, Signed)
+{
+  Magic m3 = SignedDivisionConstants(3);
+  Magic m5 = SignedDivisionConstants(5);
+  Magic m7 = SignedDivisionConstants(7);
+  Magic minus3 = SignedDivisionConstants(-3);
+  Magic minus5 = SignedDivisionConstants(-5);
+  Magic minus7 = SignedDivisionConstants(-7);
+
+  EXPECT_EQ(0x55555556, m3.multiplier);
+  EXPECT_EQ(0, m3.shift);
+  EXPECT_EQ(0x66666667, m5.multiplier);
+  EXPECT_EQ(1, m5.shift);
+  EXPECT_EQ(-0x6DB6DB6D, m7.multiplier);
+  EXPECT_EQ(2, m7.shift);
+
+  EXPECT_EQ(-0x55555556, minus3.multiplier);
+  EXPECT_EQ(0, minus3.shift);
+  EXPECT_EQ(-0x66666667, minus5.multiplier);
+  EXPECT_EQ(1, minus5.shift);
+  EXPECT_EQ(0x6DB6DB6D, minus7.multiplier);
+  EXPECT_EQ(2, minus7.shift);
+}