implementing isBigTiffType

src/bigtiffimage.cpp

@@ -38,9 +38,29 @@ namespace Exiv2
         return Image::AutoPtr(new BigTiffImage(io));
     }
 
-    bool isBigTiffType(BasicIo &, bool)
+    bool isBigTiffType(BasicIo& io, bool)
     {
-        return false;
+        byte header[2];
+        io.read(header, 2);
+
+        ByteOrder byteOrder = invalidByteOrder;
+        if (header[0] == 'I' && header[1] == 'I')
+            byteOrder = littleEndian;
+        else if (header[0] == 'M' && header[1] == 'M')
+            byteOrder = bigEndian;
+
+        bool isBigTiff = false;
+        if (byteOrder != invalidByteOrder)
+        {
+            byte version[2];
+            io.read(version, 2);
+
+            const uint16_t magic = getUShort(version, byteOrder);
+
+            isBigTiff = magic == 0x2A || magic == 0x2B;
+        }
+
+        return isBigTiff;
     }
 
 }