/usr/local/lib/swipl/library/ext/clib/sha.pl
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 hash_atom(+HashCodes, -HexAtom) is det
Convert a list of bytes (integers 0..255) into the usual hexadecimal notation. E.g. 
?- sha_hash('SWI-Prolog', Hash, []),
   hash_atom(Hash, Hex).
Hash = [61, 128, 252, 38, 121, 69, 229, 85, 199|...],
Hex = '3d80fc267945e555c730403bd0ab0716e2a68c68'.