backend_x64: Accurately handle NaNs

src/common/fp_util.h

@@ -0,0 +1,76 @@
+/* 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.
+ */
+
+#pragma once
+
+#include <boost/optional.hpp>
+
+namespace Dynarmic {
+namespace Common {
+
+/// Is 32-bit floating point value a QNaN?
+constexpr bool IsQNaN(u32 value) {
+    return (value & 0x7fc00000) == 0x7fc00000;
+}
+
+/// Is 32-bit floating point value a SNaN?
+constexpr bool IsSNaN(u32 value) {
+    return (value & 0x7fc00000) == 0x7f800000 && (value & 0x007fffff) != 0;
+}
+
+/// Is 32-bit floating point value a NaN?
+constexpr bool IsNaN(u32 value) {
+    return IsQNaN(value) || IsSNaN(value);
+}
+
+/// Given a pair of arguments, return the NaN value which would be returned by an ARM processor.
+/// If neither argument is a NaN, returns boost::none.
+inline boost::optional<u32> ProcessNaNs(u32 a, u32 b) {
+    if (IsSNaN(a)) {
+        return a | 0x00400000;
+    } else if (IsSNaN(b)) {
+        return b | 0x00400000;
+    } else if (IsQNaN(a)) {
+        return a;
+    } else if (IsQNaN(b)) {
+        return b;
+    }
+    return boost::none;
+}
+
+/// Is 64-bit floating point value a QNaN?
+constexpr bool IsQNaN(u64 value) {
+    return (value & 0x7FF8'0000'0000'0000) == 0x7FF8'0000'0000'0000;
+}
+
+/// Is 64-bit floating point value a SNaN?
+constexpr bool IsSNaN(u64 value) {
+    return (value & 0x7FF8'0000'0000'0000) == 0x7FF0'0000'0000'0000
+        && (value & 0x0007'FFFF'FFFF'FFFF) != 0;
+}
+
+/// Is 64-bit floating point value a NaN?
+constexpr bool IsNaN(u64 value) {
+    return IsQNaN(value) || IsSNaN(value);
+}
+
+/// Given a pair of arguments, return the NaN value which would be returned by an ARM processor.
+/// If neither argument is a NaN, returns boost::none.
+inline boost::optional<u64> ProcessNaNs(u64 a, u64 b) {
+    if (IsSNaN(a)) {
+        return a | 0x0008'0000'0000'0000;
+    } else if (IsSNaN(b)) {
+        return b | 0x0008'0000'0000'0000;
+    } else if (IsQNaN(a)) {
+        return a;
+    } else if (IsQNaN(b)) {
+        return b;
+    }
+    return boost::none;
+}
+
+} // namespace Common
+} // namespace Dynarmic