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functions - Default behaviour of Hash[expr] and hashing in different versions of Mathematica


In different versions of Mathematica, Wolfram silently changed the behaviour of Hash when the algorithm is not specified explicitly


Hash[1]
(* 6568131406215528669 (Version 10.1) *)

Hash[1]

(* 4371187653775642860 (Version 9.0.1) *)

Hash[1]
(* 1742717557 (Version 8.0.4) *)

This is a serious violation of how a public function/API should be supported in such a large software as Mathematica. Especially, since the documentation of Hash suggests that the behaviour will be consistent:



Hash[expr,...] will always give the same result for the same expression expr.



More importantly, the default hashing algorithms seems to be completely detached from all available settings, as it seems impossible to recreate the default hash when explicitly choosing one.



Hash[1]
(* 6568131406215528669 *)

Hash[1,#]&/@{"Adler32","CRC32","MD2","MD5","SHA","SHA256","SHA384","SHA512"}//Column
(* 
3959688615
3017272578
277753940344783714340401450212752361952
68231128815270908652080701364659390939
846778260378026149058641558857036959755342858310

35440229038221092521327873929090932360118094198559938935455836283354874680335
32975197285603495667013724312557093882636446440150950620624270433328413926233671687205762131877578287401554708845055
12579926171497332473039920596952835386489858401292624452730263741969134739018228297640298179049647746066620814234742520593670116132355345543156774710409041
*)

Does someone know, 1. how to reproduce the default hashing behaviour when explicitly choosing a method and 2. re-create the default hashing behaviour in different versions?




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