underclock/overclock SH4 option

Increase/reduce the dynarec cycle count for each block.
Issue #210

core/cfg/option.cpp

@@ -25,6 +25,7 @@ namespace config {
 // Dynarec
 
 Option<bool> DynarecEnabled("Dynarec.Enabled", true);
+Option<int> Sh4Clock("Sh4Clock", 200);
 
 // General
 

core/cfg/option.h

@@ -356,6 +356,9 @@ using OptionString = Option<std::string>;
 // Dynarec
 
 extern Option<bool> DynarecEnabled;
+#ifndef LIBRETRO
+extern Option<int> Sh4Clock;
+#endif
 
 // General
 

core/hw/sh4/dyna/decoder.cpp

@@ -1057,8 +1057,8 @@ _end:
 
 	verify(blk->oplist.size() <= BLOCK_MAX_SH_OPS_HARD);
 	
-	//make sure we don't use wayy-too-many cycles
-	blk->guest_cycles = std::min(blk->guest_cycles, max_cycles);
+	blk->guest_cycles = std::round(blk->guest_cycles * 200.f / std::max(1.f, (float)config::Sh4Clock));
+
 	//make sure we don't use wayy-too-few cycles
 	blk->guest_cycles = std::max(1U, blk->guest_cycles);
 	blk = nullptr;

core/rend/gui.cpp

@@ -2172,6 +2172,10 @@ static void gui_display_settings()
 				OptionRadioButton("Interpreter", config::DynarecEnabled, false,
 					"Use the interpreter. Very slow but may help in case of a dynarec problem");
 				ImGui::Columns(1, NULL, false);
+
+				OptionSlider("SH4 Clock", config::Sh4Clock, 100, 300,
+						"Over/Underclock the main SH4 CPU. Default is 200 MHz. Other values may crash, freeze or trigger unexpected nuclear reactions.",
+						"%d MHz");
 		    }
 	    	ImGui::Spacing();
 		    header("Network");

shell/libretro/libretro_core_options.h

@@ -689,6 +689,39 @@ struct retro_core_option_v2_definition option_defs_us[] = {
       "disabled",
 #endif
    },
+   {
+      CORE_OPTION_NAME "_sh4clock",
+      "SH4 CPU under/overclock",
+      NULL,
+      "Change the SH4 main CPU clock from the default 200 MHz. Underclocking may help slow platforms. Overclocking may increase the frame rate for some games. Use with caution.",
+      NULL,
+      "hacks",
+      {
+         { "100", "100 MHz" },
+         { "110", "110 MHz" },
+         { "120", "120 MHz" },
+         { "130", "130 MHz" },
+         { "140", "140 MHz" },
+         { "150", "150 MHz" },
+         { "160", "160 MHz" },
+         { "170", "170 MHz" },
+         { "180", "180 MHz" },
+         { "190", "190 MHz" },
+         { "200", "200 MHz" },
+         { "210", "210 MHz" },
+         { "220", "220 MHz" },
+         { "230", "230 MHz" },
+         { "240", "240 MHz" },
+         { "250", "250 MHz" },
+         { "260", "260 MHz" },
+         { "270", "270 MHz" },
+         { "280", "280 MHz" },
+         { "290", "290 MHz" },
+         { "300", "300 MHz" },
+         { NULL, NULL },
+      },
+      "200",
+   },
    {
       CORE_OPTION_NAME "_custom_textures",
       "Load Custom Textures",

shell/libretro/option.cpp

@@ -24,6 +24,7 @@ namespace config {
 // Dynarec
 
 Option<bool> DynarecEnabled("", true);
+IntOption Sh4Clock(CORE_OPTION_NAME "_sh4clock", 200);
 
 // General
 

shell/libretro/option_lr.h

@@ -202,3 +202,4 @@ extern Option<bool> PowerVR2Filter;
 extern IntOption TextureUpscale;
 extern IntOption MaxFilteredTextureSize;
 extern IntOption PerPixelLayers;
+extern IntOption Sh4Clock;