Saturate negative division

Author: kellerkindt

library/core/src/num/saturating.rs

@@ -266,19 +266,6 @@ macro_rules! saturating_impl {
         }
         forward_ref_op_assign! { impl MulAssign, mul_assign for Saturating<$t>, Saturating<$t> }
 
-        #[unstable(feature = "saturating_int_impl", issue = "87920")]
-        impl Div for Saturating<$t> {
-            type Output = Saturating<$t>;
-
-            #[inline]
-            fn div(self, other: Saturating<$t>) -> Saturating<$t> {
-                // saturating div is the default behavior?
-                Saturating(self.0.div(other.0))
-            }
-        }
-        forward_ref_binop! { impl Div, div for Saturating<$t>, Saturating<$t>,
-                #[unstable(feature = "saturating_int_impl", issue = "87920")] }
-
         #[unstable(feature = "saturating_int_impl", issue = "87920")]
         impl DivAssign for Saturating<$t> {
             #[inline]
@@ -864,6 +851,40 @@ macro_rules! saturating_int_impl_signed {
         }
         forward_ref_unop! { impl Neg, neg for Saturating<$t>,
                 #[unstable(feature = "saturating_int_impl", issue = "87920")] }
+
+        /// # Examples
+        ///
+        /// Basic usage:
+        ///
+        /// ```
+        /// #![feature(saturating_int_impl)]
+        /// use std::num::Saturating;
+        ///
+        #[doc = concat!("assert_eq!(Saturating(", stringify!($t), "::MIN + 1), Saturating(", stringify!($t), "::MAX) / Saturating(-1));")]
+        #[doc = concat!("assert_eq!(Saturating(", stringify!($t), "::MAX), Saturating(", stringify!($t), "::MIN) / Saturating(-1));")]
+        #[doc = concat!("assert_eq!(Saturating(", stringify!($t), "::MAX), Saturating(", stringify!($t), "::MAX) / Saturating(1));")]
+        #[doc = concat!("assert_eq!(Saturating(", stringify!($t), "::MIN), Saturating(", stringify!($t), "::MIN) / Saturating(1));")]
+        /// ```
+        #[unstable(feature = "saturating_int_impl", issue = "87920")]
+        impl Div for Saturating<$t> {
+            type Output = Saturating<$t>;
+
+            #[inline]
+            fn div(self, other: Saturating<$t>) -> Saturating<$t> {
+                let expected_signum = self.0.signum() * other.0.signum();
+                let (result, overflowed) = self.0.overflowing_div(other.0);
+
+                if !overflowed {
+                    Saturating(result)
+                } else if expected_signum < 0 {
+                    Saturating(<$t>::MIN)
+                } else {
+                    Saturating(<$t>::MAX)
+                }
+            }
+        }
+        forward_ref_binop! { impl Div, div for Saturating<$t>, Saturating<$t>,
+                #[unstable(feature = "saturating_int_impl", issue = "87920")] }
     )*)
 }
 
@@ -912,6 +933,18 @@ macro_rules! saturating_int_impl_unsigned {
             }
 
         }
+
+        #[unstable(feature = "saturating_int_impl", issue = "87920")]
+        impl Div for Saturating<$t> {
+            type Output = Saturating<$t>;
+
+            #[inline]
+            fn div(self, other: Saturating<$t>) -> Saturating<$t> {
+                Saturating(self.0.div(other.0))
+            }
+        }
+        forward_ref_binop! { impl Div, div for Saturating<$t>, Saturating<$t>,
+                #[unstable(feature = "saturating_int_impl", issue = "87920")] }
     )*)
 }