From 027e8be26a25584fb75dbdd0321461313a3a37ce Mon Sep 17 00:00:00 2001
From: Christopher Armstrong <radix@twistedmatrix.com>
Date: Sat, 23 Dec 2017 17:05:40 -0600
Subject: [PATCH] implement Saturating when the backend type supports
 Saturating.

Fixes #35.
---
 src/system.rs | 14 ++++++++++++++
 src/tests.rs  | 29 ++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/src/system.rs b/src/system.rs
index 6e4a8b39..27fe09bc 100644
--- a/src/system.rs
+++ b/src/system.rs
@@ -839,6 +839,20 @@ macro_rules! system {
             }
         }
 
+        impl<D, U, V> $crate::num::Saturating for Quantity<D, U, V>
+        where
+            D: Dimension + ?Sized,
+            U: Units<V> + ?Sized,
+            V: $crate::num::Saturating + $crate::num::Num + $crate::Conversion<V>,
+        {
+            fn saturating_add(self, v: Self) -> Self {
+                Quantity {value: self.value.saturating_add(v.value), ..self}
+            }
+            fn saturating_sub(self, v: Self) -> Self {
+                Quantity {value: self.value.saturating_sub(v.value), ..self}
+            }
+        }
+
         impl<D, U, V> $crate::num::Zero for Quantity<D, U, V>
         where
             D: Dimension + ?Sized,
diff --git a/src/tests.rs b/src/tests.rs
index 21452424..fce552ff 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -3,7 +3,7 @@ use self::mass::kilogram;
 #[allow(unused_imports)]
 use {Conversion, ConversionFactor};
 #[allow(unused_imports)]
-use num::{Float, FromPrimitive, One, Signed, Zero};
+use num::{Float, FromPrimitive, One, Saturating, Signed, Zero};
 use quickcheck::TestResult;
 use lib::fmt::Debug;
 use lib::marker::PhantomData;
@@ -379,6 +379,33 @@ mod quantity_macro {
 }
 
 mod system_macro {
+
+    mod int {
+        storage_types! {
+            types: PrimInt, BigInt, BigUint;
+
+            use tests::*;
+
+            Q!(tests, V);
+
+            quickcheck! {
+                #[allow(trivial_casts)]
+                fn saturating_add(l: A<V>, r: A<V>) -> bool {
+                    Test::eq(&(l.saturating_add(*r)),
+                        &(Length::new::<meter>((*l).clone())
+                            .saturating_add(Length::new::<meter>((*r).clone())).get(meter)))
+                }
+
+                #[allow(trivial_casts)]
+                fn saturating_sub(l: A<V>, r: A<V>) -> bool {
+                    Test::eq(&(l.saturating_sub(*r)),
+                        &(Length::new::<meter>((*l).clone())
+                            .saturating_sub(Length::new::<meter>((*r).clone())).get(meter)))
+                }
+            }
+        }
+    }
+
     storage_types! {
         use tests::*;