From 40d4d80c255c9043e4692d05542ddaa8182de90b Mon Sep 17 00:00:00 2001
From: zeromus <zeromus@users.sf.net>
Date: Fri, 18 Mar 2016 00:36:55 +0000
Subject: [PATCH] (winport) fix: #1543 fex identifying ROMs as compressed
 archives, causing crash (added a method to attempt to ID any kind of NDS rom
 before even passing it to FEX)

---
 desmume/src/utils/decrypt/header.cpp | 45 ++++++++++++++++++++++++----
 desmume/src/utils/decrypt/header.h   |  3 ++
 desmume/src/windows/OpenArchive.cpp  | 10 +++++++
 3 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/desmume/src/utils/decrypt/header.cpp b/desmume/src/utils/decrypt/header.cpp
index 5fb07011f..2d890c29d 100644
--- a/desmume/src/utils/decrypt/header.cpp
+++ b/desmume/src/utils/decrypt/header.cpp
@@ -26,7 +26,7 @@
 //#include "ndstool.h"
 //#include "banner.h"
 //#include "sha1.h"
-//#include "crc.h"
+#include "crc.h"
 //#include "bigint.h"
 //#include "arm7_sha1_homebrew.h"
 //#include "arm7_sha1_nintendo.h"
@@ -58,10 +58,22 @@
 ///*
 // * CalcLogoCRC
 // */
-//unsigned short CalcLogoCRC(Header &header)
-//{
-//	return CalcCrc16((unsigned char *)&header + 0xC0, 156);
-//}
+
+extern unsigned short crc16tab[];
+static short MyCalcCrc(unsigned char *data, unsigned int length)
+{
+	short crc = (short)~0;
+	for (unsigned int i=0; i<length; i++)
+	{
+		crc = (crc >> 8) ^ crc16tab[(crc ^ data[i]) & 0xFF];
+	}
+	return crc;
+}
+
+unsigned short CalcLogoCRC(Header &header)
+{
+	return MyCalcCrc((unsigned char *)&header + 0xC0, 156);
+}
 //
 /*
  * DetectRomType
@@ -656,3 +668,26 @@ int DetectRomType(const Header &header, char *secure)
 //
 //	fclose(fNDS);
 //}
+
+
+bool CheckLogoCRC(void* bytes512)
+{
+	Header* header = (Header*)bytes512;
+	unsigned short crc = CalcLogoCRC(*header); //this isn't working, don't know why
+	return header->logo_crc == crc;
+}
+
+bool DetectAnyRom(void* bytes512)
+{
+	//if(CheckLogoCRC(bytes512)) return true; //this isn't working
+
+	//use other heuristics
+	Header* header = (Header*)bytes512;
+	//at least we have 5 bytes to ID here, not bad
+	if(header->rom_header_size != 0x4000) return false;
+	if(header->logo[0] != 0x24) return false;
+	if(header->logo_crc != 0xCF56) return false;
+	//if(header->zero[0] != 0) return false; //not sure if some weird demos will be packing data in here
+	
+	return true;
+}
\ No newline at end of file
diff --git a/desmume/src/utils/decrypt/header.h b/desmume/src/utils/decrypt/header.h
index 5009673c9..89b93899a 100644
--- a/desmume/src/utils/decrypt/header.h
+++ b/desmume/src/utils/decrypt/header.h
@@ -124,6 +124,9 @@ int HashAndCompareWithList(char *filename, unsigned char sha1[]);
 int DetectRomType(const Header& header, char* secure);
 unsigned short CalcSecureAreaCRC(bool encrypt);
 
+bool CheckLogoCRC(void* bytes512);
+bool DetectAnyRom(void* bytes512);
+
 #define ROMTYPE_HOMEBREW	0
 #define ROMTYPE_MULTIBOOT	1
 #define ROMTYPE_NDSDUMPED	2	// decrypted secure area
diff --git a/desmume/src/windows/OpenArchive.cpp b/desmume/src/windows/OpenArchive.cpp
index b81865f02..8cf939175 100644
--- a/desmume/src/windows/OpenArchive.cpp
+++ b/desmume/src/windows/OpenArchive.cpp
@@ -30,6 +30,7 @@
 
 #include "resource.h"
 #include "main.h"
+#include "utils/decrypt/header.h"
 
 static char Str_Tmp[1024];
 
@@ -414,6 +415,15 @@ bool ObtainFile(const char* Name, char *const & LogicalName, char *const & Physi
 
 	while(true)
 	{
+		//before sending to FEX, see if we're known to be an NDS file
+		//(this will stop games beginning with the name ZOO from being mis-recognized as a zoo file)
+		FILE* inf = fopen(PhysicalName,"rb");
+		u8 bytes512[512];
+		bool got512 = fread(bytes512,1,512,inf)==512;
+		fclose(inf);
+		if(got512 && DetectAnyRom(bytes512))
+			return true;
+
 		ArchiveFile archive (PhysicalName);
 		if(!archive.IsCompressed())
 		{