Data commit

Task/Isqrt-integer-square-root-of-X/Prolog/isqrt-integer-square-root-of-x.pro

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+%%% -*- Prolog -*-
+%%%
+%%% The Rosetta Code integer square root task, for SWI Prolog.
+%%%
+
+%% pow4gtx/2 -- Find a power of 4 greater than X.
+pow4gtx(X, Q) :- pow4gtx(X, 1, Q), !.
+pow4gtx(X, A, Q) :- X < A, Q is A.
+pow4gtx(X, A, Q) :- A1 is A * 4,
+                    pow4gtx(X, A1, Q).
+
+%% isqrt/2 -- Find integer square root.
+%% isqrt/3 -- Find integer square root and remainder.
+isqrt(X, R) :- isqrt(X, R, _).
+isqrt(X, R, Z) :- pow4gtx(X, Q),
+                  isqrt(X, Q, 0, X, R, Z).
+isqrt(_, 1, R0, Z0, R, Z) :- R is R0,
+                             Z is Z0.
+isqrt(X, Q, R0, Z0, R, Z) :- Q1 is Q // 4,
+                             T is Z0 - R0 - Q1,
+                             (T >= 0
+                             -> R1 is (R0 // 2) + Q1,
+                                isqrt(X, Q1, R1, T, R, Z)
+                             ;  R1 is R0 // 2,
+                                isqrt(X, Q1, R1, Z0, R, Z)).
+
+roots(N) :- roots(0, N).
+roots(I, N) :- isqrt(I, R),
+               write(R),
+               (I =:= N; write(" ")),
+               I1 is I + 1,
+               (N < I1, !; roots(I1, N)).
+
+rootspow7(N) :- rootspow7(1, N).
+rootspow7(I, N) :- Pow7 is 7**I,
+                   isqrt(Pow7, R),
+                   format("~t~D~2|~t~D~87|~t~D~131|~n",
+                          [I, Pow7, R]),
+                   I1 is I + 2,
+                   (N < I1, !; rootspow7(I1, N)).
+
+main :-
+  format("isqrt(i) for 0 <= i <= 65:~2n"),
+  roots(65),
+  format("~3n"),
+  format("isqrt(7**i) for 1 <= i <= 73, i odd:~2n"),
+  format("~t~s~2|~t~s~87|~t~s~131|~n",
+         ["i", "7**i", "isqrt(7**i)"]),
+  format("-----------------------------------------------------------------------------------------------------------------------------------~n"),
+  rootspow7(73),
+  halt.
+
+:- initialization(main).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%% Instructions for GNU Emacs--
+%%% local variables:
+%%% mode: prolog
+%%% prolog-indent-width: 2
+%%% end:
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%