public boolean isValidIndex(int index) throws IOException {
        return provider.isValidIndex(index & GConv.INT_MASK);
    }
Returns true if the specified index into 
the underlying byte provider is valid.
@param index the index in the byte provider
@return returns true if the specified index is valid
@exception IOException if an I/O error occurs
GPL/DMG/src/dmg/java/mobiledevices/dmg/ghidra/GBinaryReader.java