From 3ff38b6bfe39da9355f56c6203887f164cba4072 Mon Sep 17 00:00:00 2001
From: Jonathan Campbell <jonathan@castus.tv>
Date: Sun, 16 Jun 2024 22:35:55 -0700
Subject: [PATCH] DOS drive cache: Fix directory listing performance issues by
 deferring filename sort until after all entries have been added.
 [https://github.com/joncampbell123/dosbox-x/issues/5039]

---
 CHANGELOG               |  3 +++
 include/dos_system.h    |  2 +-
 src/dos/drive_cache.cpp | 11 +++++++----
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 8fc555e4ae..c1289de393 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,4 +1,7 @@
 Next:
+  - DOS drive cache: When listing a directory, defer the filename sort until
+    the entire list is built. This improves directory listing performance
+    in directories with many files. (joncampbell123).
   - INT 10h, if instructed, will now use the video parameter table to set
     standard VGA modes instead of internal logic. (joncampbell123).
   - Removed erroneous VGA display compensation code for certain EGA/VGA
diff --git a/include/dos_system.h b/include/dos_system.h
index 43de12d5df..e4e348f68d 100644
--- a/include/dos_system.h
+++ b/include/dos_system.h
@@ -270,7 +270,7 @@ class DOS_Drive_Cache {
 	CFileInfo*	FindDirInfo		(const char* path, char* expandedPath);
 	bool		RemoveSpaces		(char* str);
 	bool		OpenDir			(CFileInfo* dir, const char* expand, uint16_t& id);
-    char*       CreateEntry     (CFileInfo* dir, const char* name, const char* sname, bool is_directory);
+    char*       CreateEntry     (CFileInfo* dir, const char* name, const char* sname, bool is_directory, bool skipSort=false);
 	void		CopyEntry		(CFileInfo* dir, CFileInfo* from);
 	uint16_t		GetFreeID		(CFileInfo* dir);
 	void		Clear			(void);
diff --git a/src/dos/drive_cache.cpp b/src/dos/drive_cache.cpp
index 70d545b1d5..13b84ca226 100644
--- a/src/dos/drive_cache.cpp
+++ b/src/dos/drive_cache.cpp
@@ -824,7 +824,7 @@ bool DOS_Drive_Cache::OpenDir(CFileInfo* dir, const char* expand, uint16_t& id)
     return false;
 }
 
-char* DOS_Drive_Cache::CreateEntry(CFileInfo* dir, const char* name, const char* sname, bool is_directory) {
+char* DOS_Drive_Cache::CreateEntry(CFileInfo* dir, const char* name, const char* sname, bool is_directory, bool skipSort) {
     CFileInfo* info = new CFileInfo;
     strcpy(info->shortname, sname);
 	strcpy(info->orgname, name);
@@ -835,7 +835,7 @@ char* DOS_Drive_Cache::CreateEntry(CFileInfo* dir, const char* name, const char*
     if (sname[0]==0) CreateShortName(dir, info);
 
     // keep list sorted (so GetLongName works correctly, used by CreateShortName in this routine)
-    if (dir->fileList.size()>0) {
+    if (dir->fileList.size()>0 && !skipSort) {
         if (!(strcmp(info->shortname,dir->fileList.back()->shortname)<0)) {
             // append at end of list
             dir->fileList.push_back(info);
@@ -891,12 +891,15 @@ bool DOS_Drive_Cache::ReadDir(uint16_t id, char* &result, char * &lresult) {
         char dir_name[CROSS_LEN], dir_sname[DOS_NAMELENGTH+1];
         bool is_directory;
         if (drive->read_directory_first(dirp, dir_name, dir_sname, is_directory)) {
-            CreateEntry(dirSearch[id], dir_name, dir_sname, is_directory);
+            CreateEntry(dirSearch[id], dir_name, dir_sname, is_directory, /*skip search*/true);
             while (drive->read_directory_next(dirp, dir_name, dir_sname, is_directory)) {
-                CreateEntry(dirSearch[id], dir_name, dir_sname, is_directory);
+                CreateEntry(dirSearch[id], dir_name, dir_sname, is_directory, /*skip search*/true);
             }
         }
 
+        // Insertion skipped sorting, now sort in one go, which should be faster when faced with many files
+        std::sort(dirSearch[id]->fileList.begin(), dirSearch[id]->fileList.end(), SortByName);
+
         // close dir
         drive->closedir(dirp);