Merge pull request #417 from notoria/mediants

Implemented predicate mediants/2 with Stern-Brocot tree

src/prolog/lib/arithmetic.pl

@@ -1,6 +1,10 @@
-:- module(arithmetic, [msb/2, lsb/2]).
+:- module(arithmetic, [lsb/2, msb/2, number_to_rational/2,
+                       number_to_rational/3,
+                       rational_numerator_denominator/3]).
 
+:- use_module(library(charsio), [write_term_to_chars/3]).
 :- use_module(library(error)).
+:- use_module(library(lists), [append/3, member/2]).
 
 lsb(X, N) :-
     builtins:must_be_number(X, lsb/2),
@@ -25,3 +29,80 @@ msb_(X, M, N) :-
     X1 is X >> 1,
     M1 is M + 1,
     msb_(X1, M1, N).
+
+number_to_rational(Real0, Fraction) :-
+    (   var(Real0) -> instantiation_error(number_to_rational/2)
+    ;   Real0 = R1/R2 ->
+        (   member(R, [R1, R2]), \+ number(R) ->
+                type_error(number, R, number_to_rational/2)
+        ;   Real = R1/R2
+        )
+    ;   number(Real0),
+        Real = Real0/1
+    ),
+    number_to_rational(1.0e-6/1, Real, Fraction).
+
+% If 0 <= Eps0 <= 1e-16 then the search is for "infinite" precision.
+number_to_rational(Eps0, Real0, Fraction) :-
+    (   var(Eps0) -> instantiation_error(number_to_rational/3)
+    ;   Eps0 = E0/E1 ->
+        (   member(E, [E0, E1]), \+ number(E) ->
+                type_error(number, E, number_to_rational/3)
+        ;   Eps = E0/E1
+        )
+    ;   number(Eps0),
+        Eps = Eps0/1
+    ),
+    (   var(Real0) -> instantiation_error(number_to_rational/3)
+    ;   Real0 = R1/R2 ->
+        (   member(R, [R1, R2]), \+ number(R) ->
+                type_error(number, R, number_to_rational/3)
+        ;   Real = R1/R2
+        )
+    ;   number(Real0),
+        Real = Real0/1
+    ),
+    E0/E1 = Eps,
+    P0/Q0 = Real,
+    S is sign(E0) * sign(E1),
+    (   S < 0 -> domain_error(not_less_than_zero, Eps0, number_to_rational/3)
+    ;   P1 is abs(P0),
+        Q1 is abs(Q0),
+        Qn1n is P1 * E1 - Q1 * E0,
+        Qn1d is Q1 * E1,
+        Qn1 = Qn1n/Qn1d,
+        Qp1n is P1 * E1 + Q1 * E0,
+        Qp1d = Qn1d,
+        Qp1 = Qp1n/Qp1d,
+        stern_brocot_(Qn1, Qp1, 0/1, 1/0, P2/Q2),
+        P3 is sign(P0) * sign(Q0) * P2,
+        Fraction is P3 rdiv Q2
+    ).
+
+number(X) :-
+    (   integer(X)
+    ;   float(X)
+    ;   rational(X)
+    ).
+
+stern_brocot_(Qnn/Qnd, Qpn/Qpd, A/B, C/D, Fraction) :-
+    Fn1 is A + C,
+    Fd1 is B + D,
+    simplify_fraction(Fn1/Fd1, Fn/Fd),
+    S1 is sign(Fn * Qnd - Fd * Qnn),
+    S2 is sign(Fn * Qpd - Fd * Qpn),
+    (   S1 < 0 -> stern_brocot_(Qnn/Qnd, Qpn/Qpd, Fn/Fd, C/D, Fraction)
+    ;   S2 > 0 -> stern_brocot_(Qnn/Qnd, Qpn/Qpd, A/B, Fn/Fd, Fraction)
+    ;   Fraction = Fn/Fd
+    ).
+
+simplify_fraction(A0/B0, A/B) :-
+    G is gcd(A0, B0),
+    A is A0 div G,
+    B is B0 div G.
+
+rational_numerator_denominator(R, N, D) :-
+    write_term_to_chars(R, [], Cs),
+    append(Ns, [' ', r, d, i, v, ' '|Ds], Cs),
+    number_chars(N, Ns),
+    number_chars(D, Ds).

src/prolog/machine/code_repo.rs

@@ -53,12 +53,23 @@ impl CodeRepo {
         self.term_dir
             .get_mut(&key)
             .map(|entry| {
-                (
-                    Predicate((entry.0).0.drain(len..).collect()),
-                    entry.1.drain(queue_len..).collect(),
-                )
+                let terms =
+                    if len < (entry.0).0.len() {
+                        (entry.0).0.drain(len ..).collect()
+                    } else {
+                        vec![]
+                    };
+
+                let queue =
+                    if queue_len < entry.1.len() {
+                        entry.1.drain(queue_len ..).collect()
+                    } else {
+                        VecDeque::new()
+                    };
+
+                (Predicate(terms), queue)
             })
-            .unwrap_or((Predicate::new(), VecDeque::from(vec![])))
+            .unwrap_or((Predicate::new(), VecDeque::new()))
     }
 
     pub(crate)

src/prolog/machine/term_expansion.rs

@@ -181,6 +181,7 @@ impl<'a> TermStream<'a> {
             te_len,
             te_queue_len,
         );
+
         let goal_expansion_additions = self.wam.code_repo.truncate_terms(
             (clause_name!("goal_expansion"), 2),
             ge_len,