Thanks for testing that. I uploaded version 0.05 a couple of days ago that implemented the dual macro, but did not set the define(s) in the Makefile.PL (I forgot!). The defines used are from Digest::MD5 which have quite a complex makefile setup. Anyway I also changed from using long to perl's U32. Now although the macro must still be the old simple macro it seems to pass on the 64 bit systems it was failing on before (4 of them).

To test the theory that although perl warns you that you can't depend on U32 being exactly 32 bits wide I uploaded Test::U32 - so far it has not detected a failure case. I will be interesting to know.