31 lines
586 B
Plaintext
31 lines
586 B
Plaintext
:- module gray.
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:- interface.
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:- import_module int.
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:- type gray.
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% VALUE conversion functions
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:- func gray.from_int(int) = gray.
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:- func gray.to_int(gray) = int.
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% REPRESENTATION conversion predicate
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:- pred gray.coerce(gray, int).
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:- mode gray.coerce(in, out) is det.
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:- mode gray.coerce(out, in) is det.
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:- implementation.
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:- import_module list.
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:- type gray
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---> gray(int).
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gray.from_int(X) = gray(X `xor` (X >> 1)).
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gray.to_int(gray(G)) = (G > 0 -> G `xor` gray.to_int(gray(G >> 1))
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; G).
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gray.coerce(gray(I), I).
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:- end_module gray.
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