Improved WiiVC check to avoid false positives & added functions to read and manipulate fcr31 (#669)

* Added functions to access and manipulate the fcr31 register

* Improved WiiVC emulator check to avoid false positives

* Updated comments

* Moved float.h to include directory

asm/fcr31.s

@@ -0,0 +1,69 @@
+.include "macros.inc"
+.section .text, "ax"
+.set noreorder
+.set noat
+
+glabel fcr_get_rounding_mode
+cfc1 $v0, $31
+jr $ra
+andi $v0, 0x3
+
+glabel fcr_set_rounding_mode
+cfc1 $t0, $31
+xor $at, $t0, $a0
+andi $at, $at, 0x3
+xor $at, $at, $t0
+jr $ra
+ctc1 $at, $31
+
+glabel fcr_get_enabled_exceptions
+cfc1 $v0, $31
+srl $v0, $v0, 7
+jr $ra
+andi $v0, $v0, 0x1f
+
+glabel fcr_set_enabled_exceptions
+cfc1 $t0, $31
+sll $a0, $a0, 7
+xor $at, $t0, $a0
+andi $at, $at, 0xf80
+xor $at, $at, $t0
+jr $ra
+ctc1 $at, $31
+
+glabel fcr_enable_exceptions
+cfc1 $at, $31
+andi $a0, $a0, 0x1f
+sll $a0, $a0, 7
+or $at, $at, $a0
+jr $ra
+ctc1 $at, $31
+
+glabel fcr_disable_exceptions
+cfc1 $at, $31
+andi $a0, $a0, 0x1f
+sll $a0, $a0, 7
+or $at, $at, $a0
+subu $at, $at, $a0
+jr $ra
+ctc1 $at, $31
+
+glabel fcr_get_cause
+cfc1 $v0, $31
+srl $v0, $v0, 12
+jr $ra
+andi $v0, $v0, 0x3f
+
+glabel fcr_get_flags
+cfc1 $v0, $31
+srl $v0, $v0, 2
+jr $ra
+andi $v0, $v0, 0x1f
+
+glabel fcr_clear_flags
+cfc1 $t0, $31
+xor $at, $t0, $0
+andi $at, $at, 0x7c
+xor $at, $at, $t0
+jr $ra
+ctc1 $at, $31

include/float.h

@@ -0,0 +1,58 @@
+#ifndef GAME_FLOAT_H
+#define GAME_FLOAT_H
+
+#include "types.h"
+
+typedef enum {
+    FRC_RM_ROUND_TO_NEAREST = 0x0,
+    FRC_RM_ROUND_TO_ZERO = 0x1,
+    FRC_RM_ROUND_TO_POSITIVE_INFINITY = 0x2,
+    FRC_RM_ROUND_TO_MINUS_INFINITY = 0x3
+} FloatRoundingMode;
+
+typedef enum {
+    FRC_EXCEPTION_INEXACT_OPERATION = 0x1,
+    FRC_EXCEPTION_UNDERFLOW = 0x2,
+    FRC_EXCEPTION_OVERFLOW = 0x4,
+    FRC_EXCEPTION_DIVISION_BY_ZERO = 0x8,
+    FRC_EXCEPTION_INVALID_OPERATION = 0x10,
+    FRC_EXCEPTION_UNIMPLEMENTED_OPERATION = 0x20 // only for Cause bits
+} FloatExceptionBits;
+
+extern FloatRoundingMode fcr_get_rounding_mode(void);
+extern void fcr_set_rounding_mode(FloatRoundingMode);
+
+// Get the Enable bits in FCR31
+extern FloatExceptionBits fcr_get_enabled_exceptions(void);
+
+// Set the Enable bits in FCR31 to the given bitset
+// NOTE: Ares is currently the only emulator to actually respect the Enable bits.
+//       Floating point exceptions will still not occur on other emulators.
+extern void fcr_set_enabled_exceptions(FloatExceptionBits);
+
+// Set the Enable bits to 1 for the given exception(s). Do not change any other exceptions.
+// NOTE: Ares is currently the only emulator to actually respect the Enable bits.
+//       Floating point exceptions will still not occur on other emulators.
+extern void fcr_enable_exceptions(FloatExceptionBits);
+
+// Set the Enable bits to 0 for the given exception(s). Do not change any other exceptions.
+extern void fcr_disable_exceptions(FloatExceptionBits);
+
+// Returns TRUE if all of the given exceptions are enabled
+inline Bool32 fcr_check_exceptions_enabled(FloatExceptionBits exceptions) {
+    return (fcr_get_enabled_exceptions() & exceptions) == exceptions;
+}
+
+// Gets the exception(s) raised by the most recently executed floating point instruction
+extern FloatExceptionBits fcr_get_cause(void);
+
+// Gets the current exception flags. These flags are set when an exception would be raised,
+// but the exception is not currently enabled. They are only cleared by calling fcr_clear_flags.
+// NOTE: This currently will only work on console and Ares. Other emulators will always return 0
+extern FloatExceptionBits fcr_get_flags(void);
+
+// Clear the current exception flags
+extern void fcr_clear_flags(void);
+
+#endif
+

sm64.ld

@@ -162,6 +162,7 @@ SECTIONS
 #endif
       KEEP(BUILD_DIR/asm/pj64_get_count_factor_asm.o(.text*));
       KEEP(BUILD_DIR/asm/round.o(.text*));
+      KEEP(BUILD_DIR/asm/fcr31.o(.text*));
 
       BUILD_DIR/src/boot*.o(.text*);
       BUILD_DIR/src/hvqm*.o(.text*);

src/game/emutest.c

@@ -8,6 +8,7 @@
 #include <ultra64.h>
 #include <string.h>
 #include "emutest_vc.h"
+#include "float.h"
 #include "types.h"
 
 extern OSMesgQueue gSIEventMesgQueue;
@@ -90,18 +91,22 @@ void detect_emulator() {
     }
     
     /*
-     * This check forces RTZ bug on vc
-     * If console is N64/adequate Emu round-to-nearest (RTN) rounding mode is used
-     * If console is VC round-to-zero (RTZ) mode is used
+     * This check forces RZ bug on vc
+     * If console is N64/adequate Emu, the current rounding mode, which is initialized to round-to-nearest (RN), is used
+     * If console is VC round-to-zero (RZ) mode is always used
      *
      * The double value 0.9999999999999999 used is 0x3FEFFFFFFFFFFFFF in binary
      * Exponent=01111111110, Mantissa=1111111111111111111111111111111111111111111111111111
-     * RTZ will output not 1.0f, RTN will output exactly 1.0f
+     * RZ will output not 1.0f, RN will output exactly 1.0f
     */
+    const FloatRoundingMode roundingMode = fcr_get_rounding_mode();
+    fcr_set_rounding_mode(FRC_RM_ROUND_TO_NEAREST);
     if (1.0f != round_double_to_float(0.9999999999999999)) {
         gEmulator = EMU_WIIVC;
+        fcr_set_rounding_mode(roundingMode);
         return;
     }
+    fcr_set_rounding_mode(roundingMode);
 
     // Perform a read from unmapped PIF ram.
     // On console and well behaved emulators, this echos back the lower half of