Introduce temporary function to advance the global rng state and discard results

Source/engine/random.cpp

@@ -29,6 +29,14 @@ uint32_t GetLCGEngineState()
 	return sglGameSeed;
 }
 
+void DiscardRandomValues(unsigned count)
+{
+	while (count != 0) {
+		GenerateSeed();
+		count--;
+	}
+}
+
 uint32_t GenerateSeed()
 {
 	sglGameSeed = (RndMult * sglGameSeed) + RndInc;

Source/engine/random.hpp

@@ -29,6 +29,14 @@ void SetRndSeed(uint32_t seed);
  */
 uint32_t GetLCGEngineState();
 
+/**
+ * @brief Advance the global RandomNumberEngine state by the specified number of rounds
+ *
+ * Only used to maintain vanilla compatibility until logic requiring reproducable random number generation is isolated.
+ * @param count How many values to discard
+ */
+void DiscardRandomValues(unsigned count);
+
 /**
  * @brief Advances the global RandomNumberEngine state and returns the new value
  */
@@ -46,7 +54,7 @@ uint32_t GenerateSeed();
  *
  * @return A random number in the range [0,2^31) or -2^31
  */
-int32_t AdvanceRndSeed();
+[[nodiscard]] int32_t AdvanceRndSeed();
 
 /**
  * @brief Generates a random integer less than the given limit using the vanilla RNG

Source/items.cpp

@@ -1464,7 +1464,7 @@ _unique_items CheckUnique(Item &item, int lvl, int uper, bool recreate)
 	if (numu == 0)
 		return UITEM_INVALID;
 
-	AdvanceRndSeed();
+	DiscardRandomValues(1);
 	uint8_t itemData = 0;
 	while (numu > 0) {
 		if (uok[itemData])
@@ -2156,7 +2156,7 @@ void RecreateWitchItem(const Player &player, Item &item, _item_indexes idx, int
 		GetItemAttrs(item, idx, lvl);
 	} else if (gbIsHellfire && idx >= 114 && idx <= 117) {
 		SetRndSeed(iseed);
-		AdvanceRndSeed();
+		DiscardRandomValues(1);
 		GetItemAttrs(item, idx, lvl);
 	} else {
 		SetRndSeed(iseed);
@@ -2299,18 +2299,15 @@ std::string GetTranslatedItemNameMagical(const Item &item, bool hellfireItem, bo
 	int minlvl;
 	int maxlvl;
 	if ((item._iCreateInfo & CF_SMITHPREMIUM) != 0) {
-		AdvanceRndSeed(); // RndVendorItem
-		AdvanceRndSeed(); // GetItemAttrs
+		DiscardRandomValues(2); // RndVendorItem and GetItemAttrs
 		minlvl = lvl / 2;
 		maxlvl = lvl;
 	} else if ((item._iCreateInfo & CF_BOY) != 0) {
-		AdvanceRndSeed(); // RndVendorItem
-		AdvanceRndSeed(); // GetItemAttrs
+		DiscardRandomValues(2); // RndVendorItem and GetItemAttrs
 		minlvl = lvl;
 		maxlvl = lvl * 2;
 	} else if ((item._iCreateInfo & CF_WITCH) != 0) {
-		AdvanceRndSeed(); // RndVendorItem
-		AdvanceRndSeed(); // GetItemAttrs
+		DiscardRandomValues(2); // RndVendorItem and GetItemAttrs
 		int iblvl = -1;
 		if (GenerateRnd(100) <= 5)
 			iblvl = 2 * lvl;
@@ -2319,11 +2316,11 @@ std::string GetTranslatedItemNameMagical(const Item &item, bool hellfireItem, bo
 		minlvl = iblvl / 2;
 		maxlvl = iblvl;
 	} else {
-		AdvanceRndSeed(); // GetItemAttrs
+		DiscardRandomValues(1); // GetItemAttrs
 		int iblvl = GetItemBLevel(lvl, item._iMiscId, onlygood, item._iCreateInfo & CF_UPER15);
 		minlvl = iblvl / 2;
 		maxlvl = iblvl;
-		AdvanceRndSeed(); // CheckUnique
+		DiscardRandomValues(1); // CheckUnique
 	}
 
 	if (minlvl > 25)
@@ -2357,8 +2354,7 @@ std::string GetTranslatedItemNameMagical(const Item &item, bool hellfireItem, bo
 		else if (!hellfireItem && FlipCoin(4)) {
 			affixItemType = AffixItemType::Staff;
 		} else {
-			AdvanceRndSeed(); // Spell
-			AdvanceRndSeed(); // Charges
+			DiscardRandomValues(2); // Spell and Charges
 
 			int preidx = GetStaffPrefixId(maxlvl, onlygood, hellfireItem);
 			if (preidx == -1 || item._iSpell == SpellID::Null) {
@@ -2394,14 +2390,13 @@ std::string GetTranslatedItemNameMagical(const Item &item, bool hellfireItem, bo
 		    [&pPrefix](const PLStruct &prefix) {
 			    pPrefix = &prefix;
 			    // GenerateRnd(prefix.power.param2 - prefix.power.param2 + 1)
-			    AdvanceRndSeed();
+			    DiscardRandomValues(1);
 			    switch (pPrefix->power.type) {
 			    case IPL_TOHIT_DAMP:
-				    AdvanceRndSeed();
-				    AdvanceRndSeed();
+				    DiscardRandomValues(2);
 				    break;
 			    case IPL_TOHIT_DAMP_CURSE:
-				    AdvanceRndSeed();
+				    DiscardRandomValues(1);
 				    break;
 			    default:
 				    break;
@@ -2503,7 +2498,7 @@ void InitItems()
 	}
 
 	if (!setlevel) {
-		AdvanceRndSeed(); /* unused */
+		DiscardRandomValues(1);
 		if (Quests[Q_ROCK].IsAvailable())
 			SpawnRock();
 		if (Quests[Q_ANVIL].IsAvailable())
@@ -4251,7 +4246,7 @@ void SpawnWitch(int lvl)
 				if (lvl >= AllItemsList[bookType].iMinMLvl) {
 					item._iSeed = AdvanceRndSeed();
 					SetRndSeed(item._iSeed);
-					AdvanceRndSeed();
+					DiscardRandomValues(1);
 					GetItemAttrs(item, bookType, lvl);
 					item._iCreateInfo = lvl | CF_WITCH;
 					item._iIdentified = true;

Source/levels/drlg_l1.cpp

@@ -701,42 +701,42 @@ void AddWall()
 				continue;
 
 			if (dungeon[i][j] == Corner) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxX = HorizontalWallOk({ i, j });
 				if (maxX != -1) {
 					HorizontalWall({ i, j }, HWall, maxX);
 				}
 			}
 			if (dungeon[i][j] == Corner) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxY = VerticalWallOk({ i, j });
 				if (maxY != -1) {
 					VerticalWall({ i, j }, VWall, maxY);
 				}
 			}
 			if (dungeon[i][j] == VWallEnd) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxX = HorizontalWallOk({ i, j });
 				if (maxX != -1) {
 					HorizontalWall({ i, j }, DWall, maxX);
 				}
 			}
 			if (dungeon[i][j] == HWallEnd) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxY = VerticalWallOk({ i, j });
 				if (maxY != -1) {
 					VerticalWall({ i, j }, DWall, maxY);
 				}
 			}
 			if (dungeon[i][j] == HWall) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxX = HorizontalWallOk({ i, j });
 				if (maxX != -1) {
 					HorizontalWall({ i, j }, HWall, maxX);
 				}
 			}
 			if (dungeon[i][j] == VWall) {
-				AdvanceRndSeed();
+				DiscardRandomValues(1);
 				int maxY = VerticalWallOk({ i, j });
 				if (maxY != -1) {
 					VerticalWall({ i, j }, VWall, maxY);

Source/levels/drlg_l3.cpp

@@ -1683,7 +1683,7 @@ void Fence()
 	for (WorldTileCoord j = 1; j < DMAXY; j++) {     // BUGFIX: Change '0' to '1' (fixed)
 		for (WorldTileCoord i = 1; i < DMAXX; i++) { // BUGFIX: Change '0' to '1' (fixed)
 			// note the comma operator is used here to advance the RNG state
-			if (dungeon[i][j] == 7 && (AdvanceRndSeed(), !IsNearThemeRoom({ i, j }))) {
+			if (dungeon[i][j] == 7 && (DiscardRandomValues(1), !IsNearThemeRoom({ i, j }))) {
 				if (FlipCoin()) {
 					int y1 = j;
 					// BUGFIX: Check `y1 >= 0` first (fixed)

Source/levels/drlg_l4.cpp

@@ -446,7 +446,7 @@ void AddWall()
 			}
 			for (auto d : { 10, 12, 13, 15, 16, 21, 22 }) {
 				if (d == dungeon[i][j]) {
-					AdvanceRndSeed();
+					DiscardRandomValues(1);
 					int x = HorizontalWallOk(i, j);
 					if (x != -1) {
 						HorizontalWall(i, j, x);
@@ -455,7 +455,7 @@ void AddWall()
 			}
 			for (auto d : { 8, 9, 11, 14, 15, 16, 21, 23 }) {
 				if (d == dungeon[i][j]) {
-					AdvanceRndSeed();
+					DiscardRandomValues(1);
 					int y = VerticalWallOk(i, j);
 					if (y != -1) {
 						VerticalWall(i, j, y);

Source/levels/themes.cpp

@@ -514,7 +514,7 @@ void Theme_Treasure(int t)
 	int treasrnd[4] = { 4, 9, 7, 10 };
 	int monstrnd[4] = { 6, 8, 3, 7 };
 
-	AdvanceRndSeed();
+	DiscardRandomValues(1);
 	for (int yp = 0; yp < MAXDUNY; yp++) {
 		for (int xp = 0; xp < MAXDUNX; xp++) {
 			if (dTransVal[xp][yp] == themes[t].ttval && IsTileNotSolid({ xp, yp })) {

Source/objects.cpp

@@ -3869,7 +3869,7 @@ void InitObjects()
 	if (currlevel == 16) {
 		AddDiabObjs();
 	} else {
-		AdvanceRndSeed();
+		DiscardRandomValues(1);
 		if (currlevel == 9 && !UseMultiplayerQuests())
 			AddSlainHero();
 		if (Quests[Q_MUSHROOM].IsAvailable())

test/random_test.cpp

@@ -25,8 +25,8 @@ TEST(RandomTest, RandomEngineParams)
 	// C++11 defines the default seed for a LCG engine as 1. The ten thousandth value is commonly used for sanity checking
 	// a sequence, so as we've had one round since state 1 we need to discard another 9998 values to get to the 10000th state.
 	// To make off by one errors more visible test the 9999th value as well as 10000th
-	for (auto i = 2; i <= 9998; i++)
-		GenerateSeed();
+	DiscardRandomValues(9997);
+
 	uint32_t expectedState = 3495122800U;
 	EXPECT_EQ(GenerateSeed(), expectedState) << "Wrong engine state after 9999 invocations";
 	expectedState = 3007658545U;