support non-BB rare enemy generation logic

src/Map.cc

@@ -683,8 +683,9 @@ string Map::Object::str() const {
       this->item_drop_checked ? "true" : "false");
 }
 
-Map::Map(uint32_t lobby_id, std::shared_ptr<PSOLFGEncryption> random_crypt)
+Map::Map(Version version, uint32_t lobby_id, std::shared_ptr<PSOLFGEncryption> random_crypt)
     : log(string_printf("[Lobby:%08" PRIX32 ":map] ", lobby_id), lobby_log.min_level),
+      version(version),
       random_crypt(random_crypt) {}
 
 void Map::clear() {
@@ -722,10 +723,27 @@ bool Map::check_and_log_rare_enemy(bool default_is_rare, uint32_t rare_rate) {
   if (default_is_rare) {
     return true;
   }
-  if ((this->rare_enemy_indexes.size() < 0x10) && (this->random_crypt->next() < rare_rate)) {
-    this->rare_enemy_indexes.emplace_back(this->enemies.size());
-    return true;
+
+  // On BB, rare enemy indexes are generated by the server and sent to the
+  // client, so we can use any method we want to choose rares. On other
+  // versions, we must match the client's logic, even though it's more
+  // computationally expensive.
+  if (this->version == Version::BB_V4) {
+    if ((this->rare_enemy_indexes.size() < 0x10) && (this->random_crypt->next() < rare_rate)) {
+      this->rare_enemy_indexes.emplace_back(this->enemies.size());
+      return true;
+    }
+
+  } else {
+    // TODO: We only need the first value from this crypt, so it's unfortunate
+    // that we have to initialize the entire thing. Find a way to make this
+    // faster.
+    PSOV2Encryption crypt(this->random_crypt->seed());
+    if ((static_cast<float>((crypt.next() >> 16) & 0xFFFF) / 65536.0f) < 0.002f) {
+      return true;
+    }
   }
+
   return false;
 }