Use safe negation in a few places

Author: tcbrindle

include/flux/op/begin_end.hpp

@@ -102,7 +102,7 @@ struct sequence_iterator {
     constexpr auto operator-=(difference_type n) -> sequence_iterator&
         requires random_access_sequence<S>
     {
-        flux::inc(*seq_, cur_, -n);
+        flux::inc(*seq_, cur_, num::neg(n));
         return *this;
     }
 
@@ -153,7 +153,7 @@ struct sequence_iterator {
         -> sequence_iterator
         requires random_access_sequence<S>
     {
-        flux::inc(*self.seq_, self.cur_, -n);
+        flux::inc(*self.seq_, self.cur_, num::neg(n));
         return self;
     }
 

include/flux/op/reverse.hpp

@@ -103,7 +103,7 @@ struct reverse_adaptor : inline_sequence_base<reverse_adaptor<Base>>
 
         static constexpr auto inc(auto& self, cursor_type& cur, distance_t dist) -> void
         {
-            flux::inc(self.base_, cur.base_cur, num::sub(distance_t{}, dist));
+            flux::inc(self.base_, cur.base_cur, num::neg(dist));
         }
 
         static constexpr auto distance(auto& self, cursor_type const& from, cursor_type const& to)

include/flux/op/stride.hpp

@@ -51,8 +51,8 @@ inline constexpr struct advance_fn {
             flux::inc(seq, cur, dist);
             return num::sub(offset, dist);
         } else if (offset < 0) {
-            auto dist = num::sub(distance_t{0},
-                                 (cmp::min)(flux::distance(seq, flux::first(seq), cur), -offset));
+            auto dist = num::neg((cmp::min)(flux::distance(seq, flux::first(seq), cur),
+                                            num::neg(offset)));
             flux::inc(seq, cur, dist);
             return num::sub(offset, dist);
         } else {