wad: Refactor ResFindSignature to work in chunks

kinda mucky but it works

src/w_wad.cpp

@@ -522,13 +522,29 @@ static lumpinfo_t* ResGetLumpsWad (FILE* handle, UINT16* nlmp, const char* filen
  */
 static boolean ResFindSignature (FILE* handle, char endPat[], UINT32 startpos)
 {
+	//the Wii U has rather slow filesystem access, and fgetc is *unbearable*
+	//so I reimplemented this function to buffer 128k chunks
 	char *s;
 	int c;
 
+	fseek(handle, 0, SEEK_END);
+	size_t len = ftell(handle);
+
 	fseek(handle, startpos, SEEK_SET);
+	size_t remaining = len - startpos;
+	size_t chunkpos = startpos;
+
 	s = endPat;
-	while((c = fgetc(handle)) != EOF)
-	{
+
+	//128k buffers
+	size_t buffer_size = std::min(128 * 1024 * sizeof(char), remaining);
+	char* buffer = static_cast<char*>(malloc(buffer_size));
+
+	size_t bytes_read = 0;
+	while ((bytes_read = fread(buffer, 1, buffer_size, handle)) > 0) {
+		for (size_t i = 0; i < bytes_read; i++) {
+			c = (int)buffer[i];
+
 			if (*s != c && s > endPat) // No match?
 				s = endPat; // We "reset" the counter by sending the s pointer back to the start of the array.
 			if (*s == c)
@@ -536,10 +552,19 @@ static boolean ResFindSignature (FILE* handle, char endPat[], UINT32 startpos)
 				s++;
 				if (*s == 0x00) // The array pointer has reached the key char which marks the end. It means we have matched the signature.
 				{
+					//the original function would leave the FILE* seeked to the end of the match
+					size_t foundpos = chunkpos + i + 1;
+					fseek(handle, foundpos, SEEK_SET);
+
+					free(buffer);
 					return true;
 				}
 			}
 		}
+		chunkpos += bytes_read;
+	}
+
+	free(buffer);
 	return false;
 }