def _update_offset_value(self, f, offset, size, value):
        '''
        Writes "value" into location "offset" in file "f".
        '''
        f.seek(offset, 0)
        if (size == 8):
            f.write(struct.pack('>q', value))
        else:
            f.write(struct.pack('>i', value))
Writes "value" into location "offset" in file "f".