Move cache indexing into a global object. Only load the cache file once, instead of for each song loaded. (Speedup, and simplifies Song.cpp.)

It's still written over for each file; this way, if a file load crashes, the earlier files will still be written to cache.

stepmania/src/SongCacheIndex.cpp

@@ -0,0 +1,48 @@
+#include "SongCacheIndex.h"
+#include "RageLog.h"
+#include "RageUtil.h"
+#include "Song.h"
+
+SongCacheIndex *SONGINDEX;
+
+SongCacheIndex::SongCacheIndex()
+{
+	CacheIndex.SetPath( "Cache\\index.cache" );
+	ReadCacheIndex();
+}
+
+SongCacheIndex::~SongCacheIndex()
+{
+
+}
+
+void SongCacheIndex::ReadCacheIndex()
+{
+	CacheIndex.ReadFile();	// don't care if this fails
+
+	int iCacheVersion;
+	CacheIndex.GetValueI( "Cache", "CacheVersion", iCacheVersion );
+	if( iCacheVersion == FILE_CACHE_VERSION )
+		return; /* OK */
+
+	LOG->Trace( "Cache format is out of date.  Deleting all cache files." );
+	CStringArray asCacheFileNames;
+	GetDirListing( "Cache/*.*", asCacheFileNames );
+	for( int i=0; i<asCacheFileNames.GetSize(); i++ )
+		DeleteFile( "Cache/" + asCacheFileNames[i] );
+	CacheIndex.Reset();
+}
+
+void SongCacheIndex::AddCacheIndex(const CString &path, int hash)
+{
+	CacheIndex.SetValueI( "Cache", "CacheVersion", FILE_CACHE_VERSION );
+	CacheIndex.SetValueI( "Cache", path, hash );
+	CacheIndex.WriteFile();
+}
+
+int SongCacheIndex::GetCacheHash( const CString &path )
+{
+	int iDirHash;
+	CacheIndex.GetValueI( "Cache", path, iDirHash );
+	return iDirHash;
+}