a64/config: Allow NaN emulation accuracy to be set

include/dynarmic/A64/config.h

@@ -126,6 +126,18 @@ struct UserConfig {
     /// This is only used if page_table is not nullptr.
     bool silently_mirror_page_table = true;
 
+    // The below options relate to accuracy of floating-point emulation.
+
+    /// Determines how accurate NaN handling is.
+    enum class NaNAccuracy {
+        /// Results of operations with NaNs will exactly match hardware.
+        Accurate,
+        /// Behave as if FPCR.DN is always set.
+        AlwaysForceDefaultNaN,
+        /// No special handling of NaN, other than setting default NaN when FPCR.DN is set.
+        NoChecks,
+    } floating_point_nan_accuracy = NaNAccuracy::Accurate;
+
     // Determines whether AddTicks and GetTicksRemaining are called.
     // If false, execution will continue until soon after Jit::HaltExecution is called.
     // bool enable_ticks = true; // TODO

src/backend_x64/a64_emit_x64.cpp

@@ -48,7 +48,11 @@ bool A64EmitContext::FPSCR_FTZ() const {
 }
 
 bool A64EmitContext::FPSCR_DN() const {
-    return Location().FPCR().DN();
+    return Location().FPCR().DN() || conf.floating_point_nan_accuracy == A64::UserConfig::NaNAccuracy::AlwaysForceDefaultNaN;
+}
+
+bool A64EmitContext::AccurateNaN() const {
+    return conf.floating_point_nan_accuracy == A64::UserConfig::NaNAccuracy::Accurate;
 }
 
 A64EmitX64::A64EmitX64(BlockOfCode& code, A64::UserConfig conf)

src/backend_x64/a64_emit_x64.h

@@ -26,6 +26,7 @@ struct A64EmitContext final : public EmitContext {
     bool FPSCR_RoundTowardsZero() const override;
     bool FPSCR_FTZ() const override;
     bool FPSCR_DN() const override;
+    bool AccurateNaN() const override;
 
     const A64::UserConfig& conf;
 };