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Merge pull request #443 from notoria/arithmetic

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Implemented expmod/4
This commit is contained in:
Mark Thom
2020-05-02 12:00:44 -03:00
committed by GitHub
parent 9dabce819a 7df7901532
commit c062b7c9da
1 changed files with 23 additions and 1 deletions
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24
src/prolog/lib/arithmetic.pl
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@@ -1,4 +1,4 @@
:- module(arithmetic, [lsb/2, msb/2, number_to_rational/2,
:- module(arithmetic, [expmod/4, lsb/2, msb/2, number_to_rational/2,
number_to_rational/3,
rational_numerator_denominator/3]).
@@ -6,6 +6,28 @@
:- use_module(library(error)).
:- use_module(library(lists), [append/3, member/2]).
expmod(Base, Expo, Mod, R) :-
( member(N, [Base, Expo, Mod]), var(N) -> instantiation_error(expmod/4)
; member(N, [Base, Expo, Mod]), \+ integer(N) ->
type_error(integer, N, expmod/4)
; Expo < 0 -> domain_error(not_less_than_zero, Expo, expmod/4)
; expmod_(Base, Expo, Mod, 1, R)
).
expmod_(_, _, 1, _, 0) :- !.
expmod_(_, 0, _, R, R) :- !.
expmod_(Base0, Expo0, Mod, C0, R) :-
Expo0 /\ 1 =:= 1,
C is (C0 * Base0) mod Mod,
!,
Expo is Expo0 >> 1,
Base is (Base0 * Base0) mod Mod,
expmod_(Base, Expo, Mod, C, R).
expmod_(Base0, Expo0, Mod, C, R) :-
Expo is Expo0 >> 1,
Base is (Base0 * Base0) mod Mod,
expmod_(Base, Expo, Mod, C, R).
lsb(X, N) :-
builtins:must_be_number(X, lsb/2),
( \+ integer(X) -> type_error(integer, X, lsb/2)