Implement ArmFPURoundMode.cpp

Fixes https://bugs.dolphin-emu.org/issues/12388. Might also fix
other games that have problems with float/paired instructions
in JitArm64, but I haven't tested any.

Source/Core/Common/ArmFPURoundMode.cpp

@@ -0,0 +1,78 @@
+// Copyright 2021 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include "Common/CommonTypes.h"
+#include "Common/FPURoundMode.h"
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+static u64 GetFPCR()
+{
+#ifdef _MSC_VER
+  return _ReadStatusReg(ARM64_FPCR);
+#else
+  u64 fpcr;
+  __asm__ __volatile__("mrs %0, fpcr" : "=r"(fpcr));
+  return fpcr;
+#endif
+}
+
+static void SetFPCR(u64 fpcr)
+{
+#ifdef _MSC_VER
+  _WriteStatusReg(ARM64_FPCR, fpcr);
+#else
+  __asm__ __volatile__("msr fpcr, %0" : : "ri"(fpcr));
+#endif
+}
+
+namespace FPURoundMode
+{
+static const u64 default_fpcr = GetFPCR();
+static u64 saved_fpcr = default_fpcr;
+
+void SetRoundMode(int mode)
+{
+  // We don't need to do anything here since SetSIMDMode is always called after calling this
+}
+
+void SetPrecisionMode(PrecisionMode mode)
+{
+}
+
+void SetSIMDMode(int rounding_mode, bool non_ieee_mode)
+{
+  // Flush-To-Zero (non-IEEE mode: denormal outputs are set to +/- 0)
+  constexpr u32 FZ = 1 << 24;
+
+  // lookup table for FPSCR.RN-to-FPCR.RMode translation
+  constexpr u32 rounding_mode_table[] = {
+      (0 << 22),  // nearest
+      (3 << 22),  // zero
+      (1 << 22),  // +inf
+      (2 << 22),  // -inf
+  };
+
+  const u64 base = default_fpcr & ~(0b111 << 22);
+  SetFPCR(base | rounding_mode_table[rounding_mode] | (non_ieee_mode ? FZ : 0));
+}
+
+void SaveSIMDState()
+{
+  saved_fpcr = GetFPCR();
+}
+
+void LoadSIMDState()
+{
+  SetFPCR(saved_fpcr);
+}
+
+void LoadDefaultSIMDState()
+{
+  SetFPCR(default_fpcr);
+}
+
+}  // namespace FPURoundMode