The swastika is a mirror image of a hindu symbol, so how did it end up on Hitler's Nazi Party flag?

Hitler particualry admired its versatility for branding. He successfully subverted its original meaning - it occurs in other cultures than Hindu - I recall seeing it at Dougga in modern Tunisia (with a party of Germans ironically) used in in mosaic pavements. There is athree leggesd version which is still used by neo-facist groups.