switch rare drops to stacked space logic

src/CommandFormats.hh

@@ -1826,13 +1826,13 @@ struct C_Login_DC_PC_GC_9D {
   /* 08 */ be_uint64_t hardware_id;
   /* 10 */ le_uint32_t sub_version = 0;
   /* 14 */ uint8_t is_extended = 0; // If 1, structure has extended format
-  /* 15 */ Language language = Language::JAPANESE; // 0 = JP, 1 = EN, 2 = DE, 3 = FR, 4 = ES
+  /* 15 */ Language language = Language::JAPANESE;
   /* 16 */ parray<uint8_t, 0x2> unused3; // Always zeroes
   /* 18 */ pstring<TextEncoding::ASCII, 0x10> v1_serial_number;
   /* 28 */ pstring<TextEncoding::ASCII, 0x10> v1_access_key;
   /* 38 */ pstring<TextEncoding::ASCII, 0x10> serial_number; // On XB, this is the XBL gamertag
   /* 48 */ pstring<TextEncoding::ASCII, 0x10> access_key; // On XB, this is the XBL user ID
-  /* 58 */ pstring<TextEncoding::ASCII, 0x30> serial_number2; // On DCv2, this is the hardware ID; on XB, this is the XBL gamertag
+  /* 58 */ pstring<TextEncoding::ASCII, 0x30> serial_number2; // DCv2: hardware ID; XB: XBL gamertag
   /* 88 */ pstring<TextEncoding::ASCII, 0x30> access_key2; // On XB, this is the XBL user ID
   /* B8 */ pstring<TextEncoding::ASCII, 0x10> login_character_name;
   /* C8 */

src/ItemCreator.cc

@@ -38,6 +38,7 @@ ItemCreator::ItemCreator(
     shared_ptr<const BattleRules> restrictions)
     : log(std::format("[ItemCreator:{}/{}/{}/{}] ", phosg::name_for_enum(stack_limits->version), abbreviation_for_mode(mode), abbreviation_for_difficulty(difficulty), section_id), lobby_log.min_level),
       logic_version(stack_limits->version),
+      is_legacy_replay(false),
       stack_limits(stack_limits),
       mode(mode),
       difficulty(difficulty),
@@ -286,30 +287,48 @@ ItemCreator::DropResult ItemCreator::on_monster_item_drop(EnemyType enemy_type,
   }
 }
 
+ItemData ItemCreator::check_rare_specs_and_create_rare_item(
+    const std::vector<RareItemSet::ExpandedDrop>& specs, uint8_t area, bool force_rare) {
+  if (specs.empty()) {
+    return ItemData();
+  }
+
+  // This logic differs from the original client logic. This logic "stacks" all rare rates into a single probability
+  // space, whereas the original client logic chooses a new random number for each rare spec that it checks. The
+  // stacking logic makes the order of specs irrelevant, whereas the original client logic means that later specs are
+  // actually more rare than they should be. In the original client, this only matters for boxes, because enemies could
+  // not have multiple specs. Also, the original code uses 0xFFFFFFFF as the maximum here; we use 0x100000000 instead,
+  // which makes all rare items SLIGHTLY more rare.
+  int64_t det = force_rare ? 0 : this->rand_int(0x100000000);
+  if (this->is_legacy_replay) {
+    // For some old tests, we waste a few replay values because they used the old (non-stacked) logic. New tests should
+    // not use this codepath.
+    for (size_t z = 1; z < specs.size(); z++) {
+      this->rand_int(0x100000000);
+    }
+  }
+  this->log.info_f("{} specs to check with det={:08X}", specs.size(), det);
+  for (const auto& spec : specs) {
+    if (this->log.should_log(phosg::LogLevel::L_INFO)) {
+      this->log.info_f("Checking spec {:08X} => {} with det={:08X}", spec.probability, spec.data.hex(), det);
+    }
+    det -= spec.probability;
+    if (det < 0) {
+      return this->create_rare_item(spec.data, area);
+    }
+  }
+  return ItemData();
+}
+
 ItemData ItemCreator::check_rare_specs_and_create_rare_box_item(uint8_t area, bool force_rare) {
-  ItemData item;
   if (!this->are_rare_drops_allowed()) {
-    return item;
+    return ItemData();
   }
 
   uint8_t table_index = this->table_index_for_area(area);
   Episode episode = episode_for_area(area);
-  auto rare_specs = this->rare_item_set->get_box_specs(this->mode, episode, this->difficulty, this->section_id, table_index);
-  for (const auto& spec : rare_specs) {
-    item = this->check_rate_and_create_rare_item(spec, area, force_rare);
-    if (!item.empty()) {
-      if (this->log.should_log(phosg::LogLevel::L_INFO)) {
-        auto hex = spec.data.hex();
-        this->log.info_f("Box spec {:08X} produced item {}", spec.probability, hex);
-      }
-      break;
-    }
-    if (this->log.should_log(phosg::LogLevel::L_INFO)) {
-      auto hex = spec.data.hex();
-      this->log.info_f("Box spec {:08X} did not produce item {}", spec.probability, hex);
-    }
-  }
-  return item;
+  auto specs = this->rare_item_set->get_box_specs(this->mode, episode, this->difficulty, this->section_id, table_index);
+  return this->check_rare_specs_and_create_rare_item(specs, area, force_rare);
 }
 
 uint32_t ItemCreator::rand_int(uint64_t max) {
@@ -351,35 +370,13 @@ ItemData ItemCreator::check_rare_spec_and_create_rare_enemy_item(EnemyType enemy
   // can have multiple rare drops if JSONRareItemSet is used (the other RareItemSet implementations never return
   // multiple drops for an enemy type).
   Episode episode = episode_for_area(area);
-  auto rare_specs = this->rare_item_set->get_enemy_specs(
+  auto specs = this->rare_item_set->get_enemy_specs(
       this->mode, episode, this->difficulty, this->section_id, enemy_type);
-  ItemData item;
-  for (const auto& spec : rare_specs) {
-    item = this->check_rate_and_create_rare_item(spec, area, force_rare);
-    if (!item.empty()) {
-      if (this->log.should_log(phosg::LogLevel::L_INFO)) {
-        auto hex = spec.data.hex();
-        this->log.info_f("Enemy spec {:08X} produced item {}", spec.probability, hex);
-      }
-      break;
-    }
-    if (this->log.should_log(phosg::LogLevel::L_INFO)) {
-      auto hex = spec.data.hex();
-      this->log.info_f("Enemy spec {:08X} did not produce item {}", spec.probability, hex);
-    }
-  }
-  return item;
+  return this->check_rare_specs_and_create_rare_item(specs, area, force_rare);
 }
 
-ItemData ItemCreator::check_rate_and_create_rare_item(
-    const RareItemSet::ExpandedDrop& drop, uint8_t area, bool force_rare) {
-  // Note: The original code uses 0xFFFFFFFF as the maximum here. We use 0x100000000 instead, which makes all rare
-  // items SLIGHTLY more rare.
-  if (!force_rare && ((drop.probability == 0) || (this->rand_int(0x100000000) >= drop.probability))) {
-    return ItemData();
-  }
-
-  ItemData item = drop.data;
+ItemData ItemCreator::create_rare_item(const ItemData& drop_item, uint8_t area) {
+  ItemData item = drop_item;
   if (item.can_be_encoded_in_rel_rare_table()) {
     switch (item.data1[0]) {
       case 0:

src/ItemCreator.hh

@@ -37,6 +37,10 @@ public:
     bool is_from_rare_table = false;
   };
 
+  inline void set_legacy_replay() {
+    this->is_legacy_replay = true;
+  }
+
   DropResult on_monster_item_drop(EnemyType enemy_type, uint8_t area, bool force_rare);
   DropResult on_box_item_drop(uint8_t area, bool force_rare);
   // Note: param3-6 refer to the corresponding fields of the object definition
@@ -70,6 +74,7 @@ private:
 
   phosg::PrefixedLogger log;
   Version logic_version;
+  bool is_legacy_replay;
   std::shared_ptr<const ItemData::StackLimits> stack_limits;
   GameMode mode;
   Difficulty difficulty;
@@ -123,7 +128,9 @@ private:
 
   ItemData check_rare_spec_and_create_rare_enemy_item(EnemyType enemy_type, uint8_t area, bool force_rare);
   ItemData check_rare_specs_and_create_rare_box_item(uint8_t area, bool force_rare);
-  ItemData check_rate_and_create_rare_item(const RareItemSet::ExpandedDrop& drop, uint8_t area, bool force_rare);
+  ItemData check_rare_specs_and_create_rare_item(
+      const std::vector<RareItemSet::ExpandedDrop>& specs, uint8_t area, bool force_rare);
+  ItemData create_rare_item(const ItemData& drop_item, uint8_t area);
 
   void generate_rare_weapon_bonuses(ItemData& item, Episode episode, uint32_t random_sample);
   void deduplicate_weapon_bonuses(ItemData& item) const;

src/Lobby.cc

@@ -230,6 +230,9 @@ void Lobby::create_item_creator(Version logic_version) {
       effective_section_id,
       rand_crypt,
       this->quest ? this->quest->meta.battle_rules : nullptr);
+  if (s->use_legacy_item_random_behavior) {
+    this->item_creator->set_legacy_replay();
+  }
 }
 
 uint8_t Lobby::effective_section_id() const {

src/ReplaySession.cc

@@ -365,6 +365,9 @@ ReplaySession::ReplaySession(shared_ptr<ServerState> state, FILE* input_log, boo
     if (line == "### use psov2 crypt") {
       this->state->use_psov2_rand_crypt = true;
     }
+    if (line == "### use legacy item random behavior") {
+      this->state->use_legacy_item_random_behavior = true;
+    }
     if (line.starts_with("### cc ")) {
       // ### cc $<chat command>
       if (this->clients.size() != 1) {

src/ServerState.hh

@@ -157,6 +157,7 @@ struct ServerState : public std::enable_shared_from_this<ServerState> {
   bool default_switch_assist_enabled = false;
   bool use_game_creator_section_id = false;
   bool use_psov2_rand_crypt = false; // Used in some tests
+  bool use_legacy_item_random_behavior = false; // Used in some tests
   bool rare_notifs_enabled_for_client_drops = false;
   bool default_rare_notifs_enabled_v1_v2 = false;
   bool default_rare_notifs_enabled_v3_v4 = false;

tests/DCv1-DCv2-PCv2-CrossplayPrivateDrops.test.txt

@@ -1,4 +1,5 @@
 ### use psov2 crypt
+### use legacy item random behavior
 I 35932 2025-05-22 21:56:44 - [C-1] Channel name updated: C-1 @ ip:10.37.129.2:49620
 I 35932 2025-05-22 21:56:44 - [C-1] Created
 I 35932 2025-05-22 21:56:44 - [GameServer] Client connected: C-1 via TG-9300-PC_V2-pc-game_server

tests/GC-JungleGame.test.txt

@@ -1,4 +1,5 @@
 ### use psov2 crypt
+### use legacy item random behavior
 I 39471 2025-05-21 23:39:20 - [IPStackSimulator] Virtual network N-2 connected via T-IPS-5059
 I 39471 2025-05-21 23:39:20 - [IPStackSimulator] Client opened TCP connection 23232323238C062D (10.0.1.535:1581 -> 35.35.35.35:9100) (acked_server_seq=BD656BE7, next_client_seq=4F6748DF)
 I 39471 2025-05-21 23:39:20 - [C-9] Channel name updated: C-9 @ ipss:N-2:127.0.0.1:57072