Disable set bit by rand()%20 and initRand() on GDC status read. It wa…

…s the primary cause of severe emulator lag in some PC-98 game cases, especially when palette fades are involved

CHANGELOG

@@ -1,4 +1,10 @@
 Unreleased
+  - Disabled code to randomly return GDC drawing
+    status active. The implementation was causing
+    severe performance issues. The code has not
+    been removed because it could be optimized and
+    fixed and could even follow the state of GDC
+    drawing. (joncampbell123)
   - VGA 6-bit DAC mode expand to full 8-bit range,
     instead of simple shifting (joncampbell123).
   - Fix 8254 PIT emulation (joncampbell123)

src/hardware/vga_pc98_gdc.cpp

@@ -649,8 +649,16 @@ uint8_t PC98_GDC_state::read_status(void) {
     if (rfifo_has_content())
         ret |= 0x01; // data ready
     else if (fifo_read == fifo_write) {
+#if 0 // THIS IS CAUSING SEVERE PERFORMANCE ISSUES, DISABLED!
+	// According to
+	// [http://hackipedia.org/browse.cgi/Computer/Platform/PC%2c%20NEC%20PC%2d98/Collections/Undocumented%209801%2c%209821%20Volume%202%20%28webtech.co.jp%29/io%5fdisp%2etxt]
+	// bit 3 (0x08) is supposed to indicate when the GDC is drawing. Perhaps the contributer who's
+	// pull request added this found a PC-98 game that failed to run without it. Re-enable when a
+	// higher performance implementation is possible. Also, recent commits in 2022 added actual
+	// GDC drawing functionality, so perhaps this should mirror that too?
         initRand();
         if (rand()%20<1) ret |= 0x08;
+#endif
     }
 
     return ret;