implement unify_ginteger to address FIXME in skip_max_list_cycle

src/machine/machine_state_impl.rs

@@ -278,6 +278,11 @@ impl MachineState {
         unifier.unify_fixnum(n1, value);
     }
 
+    pub fn unify_ginteger(&mut self, n1: GInteger, value: HeapCellValue) {
+        let mut unifier = DefaultUnifier::from(self);
+        unifier.unify_ginteger(n1, value);
+    }
+
     pub fn unify_big_int(&mut self, n1: TypedArenaPtr<Integer>, value: HeapCellValue) {
         let mut unifier = DefaultUnifier::from(self);
         unifier.unify_big_integer(n1, value);

src/machine/system_calls.rs

@@ -744,11 +744,9 @@ impl MachineState {
         }
 
         let target_n = self.store(self.deref(self.registers[1]));
-        self.unify_fixnum(
-            /* FIXME this is not safe */
-            unsafe { Fixnum::build_with_unchecked(brent_st.num_steps() as i64) },
-            target_n,
-        );
+        let num_steps = fixnum!(GInteger, brent_st.num_steps() as i64, &mut self.arena);
+
+        self.unify_ginteger(num_steps, target_n);
 
         if !self.fail {
             unify!(self, self.registers[4], self.heap[prev_hare]);

src/machine/unify.rs

@@ -150,6 +150,13 @@ pub(crate) trait Unifier: DerefMut<Target = MachineState> {
         );
     }
 
+    fn unify_ginteger(&mut self, n: GInteger, value: HeapCellValue) {
+        match n {
+            GInteger::Integer(integer) => self.unify_big_int(integer, value),
+            GInteger::Fixnum(fixnum) => self.unify_fixnum(fixnum, value),
+        }
+    }
+
     fn unify_atom(&mut self, atom: Atom, value: HeapCellValue) {
         read_heap_cell!(value,
             (HeapCellValueTag::Atom, (name, arity)) => {