- Ported the COMPATF2_OLD_RANDOM_GENERATOR compatibility flag from Zandronum and added it to the Doom (Strict) compatibility mode.

Added new compatflag "old random generator", controlled by the new CVAR compat_oldrandom. If this is enabled, the original Doom random table is used to generate random integers in [0,255], which should make for instance the SSG cause a little more damage.

src/d_main.cpp

@@ -598,7 +598,7 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 			COMPATF_TRACE | COMPATF_MISSILECLIP | COMPATF_SOUNDTARGET | COMPATF_NO_PASSMOBJ | COMPATF_LIMITPAIN |
 			COMPATF_DEHHEALTH | COMPATF_INVISIBILITY | COMPATF_CROSSDROPOFF | COMPATF_CORPSEGIBS | COMPATF_HITSCAN |
 			COMPATF_WALLRUN | COMPATF_NOTOSSDROPS | COMPATF_LIGHT | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_BADANGLES | COMPATF2_FLOORMOVE | COMPATF2_POINTONLINE | COMPATF2_EXPLODE2;
+		w = COMPATF2_BADANGLES | COMPATF2_FLOORMOVE | COMPATF2_POINTONLINE | COMPATF2_EXPLODE2 | COMPATF2_OLD_RANDOM_GENERATOR;
 		break;
 
 	case 3: // Boom compat mode
@@ -677,6 +677,7 @@ CVAR (Flag, compat_checkswitchrange,	compatflags2, COMPATF2_CHECKSWITCHRANGE);
 CVAR (Flag, compat_explode1,			compatflags2, COMPATF2_EXPLODE1);
 CVAR (Flag, compat_explode2,			compatflags2, COMPATF2_EXPLODE2);
 CVAR (Flag, compat_railing,				compatflags2, COMPATF2_RAILING);
+CVAR (Flag, compat_oldrandom,			compatflags2, COMPATF2_OLD_RANDOM_GENERATOR);
 
 CVAR(Bool, vid_activeinbackground, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG)
 
@@ -2123,6 +2124,7 @@ static void D_DoomInit()
 	srand(rngseed);
 		
 	FRandom::StaticClearRandom ();
+	M_ClearRandom();
 
 	if (!batchrun) Printf ("M_LoadDefaults: Load system defaults.\n");
 	M_LoadDefaults ();			// load before initing other systems

src/doomdef.h

@@ -506,6 +506,7 @@ enum : unsigned int
 	COMPATF2_EXPLODE2		= 1 << 9,	// Use original explosion code throughout.
 	COMPATF2_RAILING		= 1 << 10,	// Bugged Strife railings.
 	COMPATF2_SCRIPTWAIT		= 1 << 11,	// Use old scriptwait implementation where it doesn't wait on a non-running script.
+	COMPATF2_OLD_RANDOM_GENERATOR	= 1 << 12,	// [BB] Use Doom's random table instead of ZDoom's random number generator.
 };
 
 // Emulate old bugs for select maps. These are not exposed by a cvar

src/g_game.cpp

@@ -2683,6 +2683,7 @@ bool G_ProcessIFFDemo (FString &mapname)
 			if (mapname[0] != 0)
 			{
 				FRandom::StaticClearRandom ();
+				M_ClearRandom();
 			}
 			consoleplayer = *demo_p++;
 			break;

src/g_level.cpp

@@ -474,6 +474,7 @@ void G_InitNew (const char *mapname, bool bTitleLevel)
 			rngseed = use_staticrng ? staticrngseed : (rngseed + 1);
 		}
 		FRandom::StaticClearRandom ();
+		M_ClearRandom();
 		P_ClearACSVars(true);
 		level.time = 0;
 		level.maptime = 0;

src/m_random.cpp

@@ -60,6 +60,7 @@
 #include <assert.h>
 
 #include "doomstat.h"
+#include "doomdef.h"
 #include "m_random.h"
 #include "serializer.h"
 #include "b_bot.h"
@@ -75,6 +76,36 @@
 
 // TYPES -------------------------------------------------------------------
 
+// Doom's original random number generator.
+
+//
+// M_Random
+// Returns a 0-255 number
+//
+unsigned char rndtable[256] = {
+	0,	 8, 109, 220, 222, 241, 149, 107,  75, 248, 254, 140,  16,	66 ,
+	74,  21, 211,  47,	80, 242, 154,  27, 205, 128, 161,  89,	77,  36 ,
+	95, 110,  85,  48, 212, 140, 211, 249,	22,  79, 200,  50,	28, 188 ,
+	52, 140, 202, 120,	68, 145,  62,  70, 184, 190,  91, 197, 152, 224 ,
+	149, 104,  25, 178, 252, 182, 202, 182, 141, 197,	4,	81, 181, 242 ,
+	145,  42,  39, 227, 156, 198, 225, 193, 219,  93, 122, 175, 249,   0 ,
+	175, 143,  70, 239,  46, 246, 163,	53, 163, 109, 168, 135,   2, 235 ,
+	25,  92,  20, 145, 138,  77,  69, 166,	78, 176, 173, 212, 166, 113 ,
+	94, 161,  41,  50, 239,  49, 111, 164,	70,  60,   2,  37, 171,  75 ,
+	136, 156,  11,	56,  42, 146, 138, 229,  73, 146,  77,	61,  98, 196 ,
+	135, 106,  63, 197, 195,  86,  96, 203, 113, 101, 170, 247, 181, 113 ,
+	80, 250, 108,	7, 255, 237, 129, 226,	79, 107, 112, 166, 103, 241 ,
+	24, 223, 239, 120, 198,  58,  60,  82, 128,   3, 184,  66, 143, 224 ,
+	145, 224,  81, 206, 163,  45,  63,	90, 168, 114,  59,	33, 159,  95 ,
+	28, 139, 123,  98, 125, 196,  15,  70, 194, 253,  54,  14, 109, 226 ,
+	71,  17, 161,  93, 186,  87, 244, 138,	20,  52, 123, 251,	26,  36 ,
+	17,  46,  52, 231, 232,  76,  31, 221,	84,  37, 216, 165, 212, 106 ,
+	197, 242,  98,	43,  39, 175, 254, 145, 190,  84, 118, 222, 187, 136 ,
+	120, 163, 236, 249
+};
+
+int 	prndindex = 0;
+
 // EXTERNAL FUNCTION PROTOTYPES --------------------------------------------
 
 // PUBLIC FUNCTION PROTOTYPES ----------------------------------------------
@@ -139,6 +170,18 @@ static TDeletingArray<FRandom *> NewRNGs;
 
 // CODE --------------------------------------------------------------------
 
+// Which one is deterministic?
+int P_Random (void)
+{
+	prndindex = (prndindex+1)&0xff;
+	return rndtable[prndindex];
+}
+
+void M_ClearRandom (void)
+{
+	prndindex = 0;
+}
+
 //==========================================================================
 //
 // FRandom - Nameless constructor
@@ -230,6 +273,26 @@ FRandom::~FRandom ()
 	}
 }
 
+// [BB] Moved implementation here.
+int FRandom::operator()()
+{
+	// [BB] Use Doom's original random numbers if the user wants it.
+	if ( compatflags2 & COMPATF2_OLD_RANDOM_GENERATOR )
+		return P_Random();
+
+	return GenRand32() & 255;
+}
+
+// [BB] Moved implementation here.
+int FRandom::Random2()
+{
+	// [BB] Use Doom's original random numbers if the user wants it.
+	if ( compatflags2 & COMPATF2_OLD_RANDOM_GENERATOR )
+		return ( P_Random() - P_Random() );
+
+	return Random2(255);
+}
+
 //==========================================================================
 //
 // FRandom :: StaticClearRandom
@@ -336,6 +399,7 @@ void FRandom::StaticReadRNGState(FSerializer &arc)
 
 	// Call StaticClearRandom in order to ensure that SFMT is initialized
 	FRandom::StaticClearRandom ();
+	M_ClearRandom();
 
 	if (arc.BeginArray("rngs"))
 	{

src/m_random.h

@@ -49,10 +49,8 @@ public:
 	~FRandom ();
 
 	// Returns a random number in the range [0,255]
-	int operator()()
-	{
-		return GenRand32() & 255;
-	}
+	// [BB] Moved the implementation to m_random.cpp.
+	int operator()();
 
 	// Returns a random number in the range [0,mod)
 	int operator() (int mod)
@@ -63,10 +61,8 @@ public:
 	}
 
 	// Returns rand# - rand#
-	int Random2()
-	{
-		return Random2(255);
-	}
+	// [BB] Moved the implementation to m_random.cpp.
+	int Random2();
 
 // Returns (rand# & mask) - (rand# & mask)
 	int Random2(int mask)
@@ -224,4 +220,8 @@ extern bool use_staticrng;
 // M_Random can be used for numbers that do not affect gameplay
 extern FRandom M_Random;
 
+// Returns a number from 0 to 255, from a lookup table.
+int P_Random (void);
+void M_ClearRandom (void);
+
 #endif

wadsrc/static/language.enu

@@ -2219,6 +2219,7 @@ CMPTMNU_CHECKSWITCHRANGE	= "Enable buggy CheckSwitchRange behavior";
 CMPTMNU_EXPLODE1			= "No vertical thrust from explosions";
 CMPTMNU_EXPLODE2			= "Use original Doom explosion behavior";
 CMPTMNU_RAILINGHACK			= "Enable buggy Strife railing";
+CMPTMNU_OLDRANDOM				= "Use original Doom pseudo-RNG";
 
 // Sound Options
 SNDMNU_TITLE			= "SOUND OPTIONS";

wadsrc/static/menudef.txt

@@ -1675,6 +1675,7 @@ OptionMenu "CompatActorMenu" protected
 	Option "$CMPTMNU_INVISIBILITY",					"compat_INVISIBILITY", "YesNo"
 	Option "$CMPTMNU_MINOTAUR",						"compat_MINOTAUR", "YesNo"
 	Option "$CMPTMNU_NOTOSSDROPS",					"compat_NOTOSSDROPS", "YesNo"
+	Option "$CMPTMNU_OLDRANDOM",					"compat_oldrandom", "YesNo"
 	Class "CompatibilityMenu"
 }