Filesystem: Add a cache for finding file info by disc offset

FileMonitor calls this every time a read happens, and there's no code that
only calls this a small number of times, so having a cache is worthwhile.

Source/Core/DiscIO/FileSystemGCWii.cpp

@@ -6,6 +6,7 @@
 #include <cinttypes>
 #include <cstddef>
 #include <cstring>
+#include <map>
 #include <memory>
 #include <string>
 #include <vector>
@@ -271,27 +272,32 @@ std::unique_ptr<IFileInfo> CFileSystemGCWii::FindFileInfo(u64 disc_offset) const
 	if (!IsValid())
 		return nullptr;
 
-	return FindFileInfo(disc_offset, m_root);
+	if (m_offset_file_info_cache.empty())
+		BuildOffsetFileInfoCache(m_root);
+
+	// Get the first file that ends after disc_offset
+	auto it = m_offset_file_info_cache.upper_bound(disc_offset);
+	if (it == m_offset_file_info_cache.end())
+		return nullptr;
+	std::unique_ptr<IFileInfo> result(new CFileInfoGCWii(m_root, it->second));
+
+	// If the file's start isn't after disc_offset, success
+	if (result->GetOffset() <= disc_offset)
+		return result;
+
+	return nullptr;
 }
 
-std::unique_ptr<IFileInfo> CFileSystemGCWii::FindFileInfo(u64 disc_offset, const IFileInfo& file_info) const
+void CFileSystemGCWii::BuildOffsetFileInfoCache(const IFileInfo& directory) const
 {
-	for (const IFileInfo& child : file_info)
+	for (const IFileInfo& file_info : directory)
 	{
-		if (child.IsDirectory())
-		{
-			std::unique_ptr<IFileInfo> result = FindFileInfo(disc_offset, child);
-			if (result)
-				return result;
-		}
-		else if ((file_info.GetOffset() <= disc_offset) &&
-		         ((file_info.GetOffset() + file_info.GetSize()) > disc_offset))
-		{
-			return std::unique_ptr<IFileInfo>(new CFileInfoGCWii((const CFileInfoGCWii&)file_info));
-		}
+		if (file_info.IsDirectory())
+			BuildOffsetFileInfoCache(file_info);
+		else
+			m_offset_file_info_cache.emplace(file_info.GetOffset() + file_info.GetSize(),
+		                                     reinterpret_cast<const CFileInfoGCWii&>(file_info).m_index);
 	}
-
-	return nullptr;
 }
 
 u64 CFileSystemGCWii::ReadFile(const IFileInfo* file_info, u8* _pBuffer, u64 _MaxBufferSize, u64 _OffsetInFile) const

Source/Core/DiscIO/FileSystemGCWii.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <cstddef>
+#include <map>
 #include <string>
 #include <vector>
 
@@ -18,6 +19,8 @@ class IVolume;
 
 class CFileInfoGCWii : public IFileInfo
 {
+friend class CFileSystemGCWii;
+
 public:
 	// None of the constructors take ownership of FST pointers
 
@@ -86,9 +89,11 @@ class CFileSystemGCWii : public IFileSystem
 	bool m_Wii;
 	std::vector<u8> m_file_system_table;
 	CFileInfoGCWii m_root;
+	// Maps the end offset of files to FST indexes
+	mutable std::map<u64, u32> m_offset_file_info_cache;
 
 	std::unique_ptr<IFileInfo> FindFileInfo(const std::string& path, const IFileInfo& file_info) const;
-	std::unique_ptr<IFileInfo> FindFileInfo(u64 disc_offset, const IFileInfo& file_info) const;
+	void BuildOffsetFileInfoCache(const IFileInfo& directory) const;
 	u32 GetOffsetShift() const;
 };