Recognize our own magic hash

so that when we create GME files with MP3 files without a magic header,
we do not have to guess the XOR value.

Author: nomeata

src/Constants.hs

@@ -16,6 +16,11 @@ arithOpCode XOr  = [0xF7, 0xFF]
 -- Neg is unary, hence a Command
 arithOpCode Set  = [0xF9, 0xFF]
 
+knownRawXOR :: Word32
+knownRawXOR = 0x00000039 -- from Bauernhof
+
+knownXOR :: Word8
+knownXOR = 0xAD
 
 fileMagics :: [(BC.ByteString, String)]
 fileMagics =

src/GMEParser.hs

@@ -238,10 +238,12 @@ getBinaries = do
         binary <- getSegAt offset (BC.unpack desc) (getBS length)
         return (desc, binary)
 
-getAudios :: SGet ([B.ByteString], Bool, Word8)
-getAudios = do
+getAudios :: Word32 -> SGet ([B.ByteString], Bool, Word8)
+getAudios rawXor = do
     until <- lookAhead getWord32
-    x <- lookAhead $ jumpTo until >> getXor
+    x <- case () of
+          () | rawXor == knownRawXOR -> return knownXOR
+             | otherwise             -> lookAhead $ jumpTo until >> getXor
     offset <- bytesRead
     let n_entries = fromIntegral ((until - offset) `div` 8)
     at_doubled <- lookAhead $ do
@@ -359,13 +361,14 @@ getSpecials = (,) <$> getWord16 <*> getWord16
 getTipToiFile :: SGet TipToiFile
 getTipToiFile = getSegAt 0x00 "Header" $ do
     ttScripts <- indirection "Scripts" getScripts
-    (ttAudioFiles, ttAudioFilesDoubles, ttAudioXor) <- indirection "Media" getAudios
+    ttRawXor <- getAt 0x001C getWord32
+    (ttAudioFiles, ttAudioFilesDoubles, ttAudioXor) <- indirection "Media" (getAudios ttRawXor)
     _ <- getWord32 -- Usually 0x0000238b
     _ <- indirection "Additional script" getScript
     ttGames <- indirection "Games" $ indirections getWord32 "" getGame
     ttProductId <- getWord32
     ttInitialRegs <- indirection "Initial registers" getInitialRegs
-    ttRawXor <- getWord32
+    _ <- getWord32 -- raw Xor
     (ttComment, ttDate) <- do
         l <- getWord8
         c <- getBS (fromIntegral l)

src/TipToiYaml.hs

@@ -280,15 +280,15 @@ ttYaml2tt dir (TipToiYAML {..}) extCodeMap = do
 
     return $ (TipToiFile
         { ttProductId = ttyProduct_Id
-        , ttRawXor = 0x00000039 -- from Bauernhof
+        , ttRawXor = knownRawXOR
         , ttComment = BC.pack (fromMaybe "created with tip-toi-reveng" ttyComment)
         , ttDate = BC.pack date
         , ttWelcome = welcome
         , ttInitialRegs = [fromMaybe 0 (M.lookup r initRegs) | r <- [0..maxReg]]
         , ttScripts = scripts'
         , ttGames = []
         , ttAudioFiles = files
-        , ttAudioXor = 0xAD
+        , ttAudioXor = knownXOR
         , ttAudioFilesDoubles = False
         , ttChecksum = 0x00
         , ttChecksumCalc = 0x00