From 7d50301b46d6d9638aab3579e3a330f2cb01b267 Mon Sep 17 00:00:00 2001
From: Zachary Burke <zachary.burke@gmail.com>
Date: Tue, 2 Jan 2018 09:36:22 -0800
Subject: [PATCH] Majorly improved performance when fetching Mame names.

After profiling UI filtering and startup I determined that
getCleanMameName was responsible for the incredibly long load times when
loading/filtering Mame ROMS. This function was using a linear search
over a pre-sorted array to find a corresponding Mame ROM Name from the
ROM name. It now uses a binary search which improves UI load/filter
responsiveness by a couple orders of magnitude.

Single core performance on my i7 for 10,000 iterations was 2.01 secs vs
7.77e-4 secs
---
 es-app/src/FileData.cpp   |  2 +-
 es-app/src/PlatformId.cpp | 48 ++++++++++++++++++++++++++++++++++-----
 es-app/src/PlatformId.h   |  7 +++++-
 3 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/es-app/src/FileData.cpp b/es-app/src/FileData.cpp
index 9ba6c082d..31e636819 100644
--- a/es-app/src/FileData.cpp
+++ b/es-app/src/FileData.cpp
@@ -40,7 +40,7 @@ std::string FileData::getDisplayName() const
 {
 	std::string stem = mPath.stem().generic_string();
 	if(mSystem && mSystem->hasPlatformId(PlatformIds::ARCADE) || mSystem->hasPlatformId(PlatformIds::NEOGEO))
-		stem = PlatformIds::getCleanMameName(stem.c_str());
+		stem = PlatformIds::mameTitleSearch(stem.c_str());
 
 	return stem;
 }
diff --git a/es-app/src/PlatformId.cpp b/es-app/src/PlatformId.cpp
index bf37bc52b..e437a367c 100644
--- a/es-app/src/PlatformId.cpp
+++ b/es-app/src/PlatformId.cpp
@@ -95,16 +95,52 @@ namespace PlatformIds
 		return PlatformNames[id];
 	}
 
-	const char* getCleanMameName(const char* from)
+	int getMameTitleCount()
 	{
 		const char** mameNames = mameNameToRealName;
-
-		while(*mameNames != NULL && strcmp(from, *mameNames) != 0)
+		int count = 0;
+		while (*mameNames != NULL)
+		{
 			mameNames += 2;
+			count++;
+		}
+		return count;
+	}
 
-		if(*mameNames)
-			return *(mameNames + 1);
-		
+
+	const char* mameTitleSearch(const char* from)
+	{
+		// The start and end index range from [0, number of roms]
+		int iStart = 0;
+		static int mameCount = getMameTitleCount();
+		int iEnd = mameCount;
+
+		while (iStart < iEnd)
+		{
+			// The middle entry is halfway between the start and end index
+			const int iMiddle = (iStart + iEnd) / 2;
+
+			// mameNameToRealName contains 2 sequential entries for every entry, so the indexes look like this:
+			// 0: key, value,
+			// 2: key, value,
+			// 4: key, value
+			// This means that there are twice as many indexes as there are numbers of ROMs. So to get the
+			// iMiddle'th entry, we need to multiply by 2 because iMiddle goes from [0, number of roms].
+			const int iKey = iMiddle * 2;
+			const int comp = strcmp(mameNameToRealName[iKey], from);
+			if (comp < 0)
+			{
+				// Remember, iMiddle ranges from [0, number of roms] so we only increment by 1
+				iStart = iMiddle + 1;
+			}
+			else if (comp > 0)
+			{
+				iEnd = iMiddle;
+			}
+			// The Key was found, now return the Value
+			else return mameNameToRealName[iKey + 1];
+		}
 		return from;
 	}
+
 }
diff --git a/es-app/src/PlatformId.h b/es-app/src/PlatformId.h
index 8b08cde0f..be553e8fc 100644
--- a/es-app/src/PlatformId.h
+++ b/es-app/src/PlatformId.h
@@ -78,7 +78,12 @@ namespace PlatformIds
 	PlatformId getPlatformId(const char* str);
 	const char* getPlatformName(PlatformId id);
 
-	const char* getCleanMameName(const char* from);
+	// Get the number of Mame titles in the mameNameToRealName array
+	// Should only run this once and store in a static or cached variable
+	int getMameTitleCount();
+
+	// Perform a binary search for a game title given a rom name
+	const char* mameTitleSearch(const char* from);
 }
 
 #endif // ES_APP_PLATFORM_ID_H