ir: Add opcodes for unsigned reciprocal estimate

src/common/math_util.cpp

@@ -0,0 +1,31 @@
+/* This file is part of the dynarmic project.
+ * Copyright (c) 2018 MerryMage
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2 or any later version.
+ */
+
+#include <array>
+#include "common/math_util.h"
+
+namespace Dynarmic::Common {
+
+u8 RecipEstimate(u64 a) {
+    using LUT = std::array<u8, 256>;
+    static constexpr u64 lut_offset = 256;
+
+    static const LUT lut = [] {
+        LUT result{};
+        for (u64 i = 0; i < result.size(); i++) {
+            u64 a = i + lut_offset;
+
+            a = a * 2 + 1;
+            u64 b = (1u << 19) / a;
+            result[i] = static_cast<u8>((b + 1) / 2);
+        }
+        return result;
+    }();
+
+    return lut[a - lut_offset];
+}
+
+} // namespace Dynarmic::Common