Add '$random_integer'/3

src/lib/random.pl

@@ -15,16 +15,14 @@ the random seed. This makes everything completely reproducible.
 % Succeeds with probability 0.5.
 maybe :- '$maybe'.
 
-% The higher the precision, the slower it gets.
-random_number_precision(64).
-
 %% random(-R).
 %
 % Generates a random floating number between 0 (inclusive) and 1 (exclusive).
 random(R) :-
     var(R),
-    random_number_precision(N),
-    rnd(N, R).
+    N is 2^50,
+    '$random_integer'(0, N, K),
+    R is K/N.
 
 %% random_integer(+Lower, +Upper, -R).
 %
@@ -41,25 +39,10 @@ random_integer(Lower, Upper, R) :-
         type_error(integer, Lower, random_integer/3)
     ;   \+ integer(Upper) ->
         type_error(integer, Upper, random_integer/3)
-    ;   Upper > Lower,
-        random(R0),
-        R is floor((Upper - Lower) * R0 + Lower)
+    ;   Lower < Upper,
+        '$random_integer'(Lower, Upper, R)
     ).
 
-rnd(N, R) :-
-    rnd_(N, 0, R).
-
-rnd_(0, R, R) :- !.
-rnd_(N, R0, R) :-
-    maybe,
-    !,
-    N1 is N - 1,
-    rnd_(N1, R0, R).
-rnd_(N, R0, R) :-
-    N1 is N - 1,
-    R1 is R0 + 1.0 / 2.0 ^ N,
-    rnd_(N1, R1, R).
-
 %% set_random(+Seed).
 %
 % Sets a seed that will be used for subsequent random generations in this library.

src/machine/dispatch.rs

@@ -4061,6 +4061,14 @@ impl Machine {
                             .install_new_block(self.machine_st.registers[1]);
                         step_or_fail!(self, self.machine_st.p = self.machine_st.cp);
                     }
+                    &Instruction::CallRandomInteger => {
+                        self.random_integer();
+                        step_or_fail!(self, self.machine_st.p += 1);
+                    }
+                    &Instruction::ExecuteRandomInteger => {
+                        self.random_integer();
+                        step_or_fail!(self, self.machine_st.p = self.machine_st.cp);
+                    }
                     &Instruction::CallMaybe => {
                         self.maybe();
                         step_or_fail!(self, self.machine_st.p += 1);

src/machine/system_calls.rs

@@ -4157,6 +4157,63 @@ impl Machine {
         }
     }
 
+    #[inline(always)]
+    pub(crate) fn random_integer(&mut self) {
+        let a1 = self.deref_register(1);
+        let a2 = self.deref_register(2);
+        let value = match (Number::try_from(a1), Number::try_from(a2)) {
+            (Ok(Number::Fixnum(lower)), Ok(Number::Fixnum(upper))) => {
+                let (lower, upper) = (lower.get_num(), upper.get_num());
+                if lower >= upper {
+                    self.machine_st.fail = true;
+                    return;
+                }
+                let value = self.rng.gen_range(lower..upper);
+                Number::Fixnum(Fixnum::build_with(value))
+            }
+            (Ok(Number::Fixnum(lower)), Ok(Number::Integer(upper))) => {
+                let lower = Integer::from(lower);
+                if &lower >= &*upper {
+                    self.machine_st.fail = true;
+                    return;
+                }
+                let value = self.rng.gen_range(lower..(&*upper).clone());
+                Number::arena_from(value, &mut self.machine_st.arena)
+            }
+            (Ok(Number::Integer(lower)), Ok(Number::Fixnum(upper))) => {
+                let upper = Integer::from(upper);
+                if &*lower >= &upper {
+                    self.machine_st.fail = true;
+                    return;
+                }
+                let value = self.rng.gen_range((&*lower).clone()..upper);
+                Number::arena_from(value, &mut self.machine_st.arena)
+            }
+            (Ok(Number::Integer(lower)), Ok(Number::Integer(upper))) => {
+                if &*lower >= &*upper {
+                    self.machine_st.fail = true;
+                    return;
+                }
+                let value = self.rng.gen_range((&*lower).clone()..(&*upper).clone());
+                Number::arena_from(value, &mut self.machine_st.arena)
+            }
+            _ => {
+                self.machine_st.fail = true;
+                return;
+            }
+        };
+        let a3 = self.deref_register(3);
+        match value {
+            Number::Fixnum(n) => {
+                self.machine_st.unify_fixnum(n, a3);
+            }
+            Number::Integer(n) => {
+                self.machine_st.unify_big_int(n, a3);
+            }
+            _ => unreachable!(),
+        }
+    }
+
     #[inline(always)]
     pub(crate) fn maybe(&mut self) {
         self.machine_st.fail = self.rng.gen();