Add ClampedNumeric templates

base/numerics/safe_conversions_impl.h

Index: base/numerics/safe_conversions_impl.h
diff --git a/base/numerics/safe_conversions_impl.h b/base/numerics/safe_conversions_impl.h
index aef7135cefb8177e397a9a5729dd9282b2ff6669..713b8efbea7a0806bbc2e9693ac48592df770d92 100644
--- a/base/numerics/safe_conversions_impl.h
+++ b/base/numerics/safe_conversions_impl.h
@@ -549,6 +549,7 @@ struct UnderlyingType {
   using type = typename ArithmeticOrUnderlyingEnum<T>::type;
   static const bool is_numeric = std::is_arithmetic<type>::value;
   static const bool is_checked = false;
+  static const bool is_clamped = false;
   static const bool is_strict = false;
 };
 
@@ -590,14 +591,17 @@ template <typename L, typename R>
 struct IsClampedOp {
   static const bool value =
       UnderlyingType<L>::is_numeric && UnderlyingType<R>::is_numeric &&
-      (UnderlyingType<L>::is_clamped || UnderlyingType<R>::is_clamped);
+      (UnderlyingType<L>::is_clamped || UnderlyingType<R>::is_clamped) &&
+      !(UnderlyingType<L>::is_checked || UnderlyingType<R>::is_checked);

[dcheng, 2017/06/28 07:25:06]

This confused me a bit initially--why would we have to filter these bits out if
each type trait only sets one of the corresponding bits?

I think this is because we have some implicit conversions allowed between safe
numeric types--perhaps it's worth documenting them in the README.md as well

[jschuh, 2017/06/28 12:32:38]

I'll add it to the README. The gist is, if it can be cast directly to the
underlying type then it can be up-converted. And priority of conversion is:
StrictNumeric -> ClampedNumeric -> CheckedNumeric.

 };
 
 template <typename L, typename R>
 struct IsStrictOp {
   static const bool value =
       UnderlyingType<L>::is_numeric && UnderlyingType<R>::is_numeric &&
-      (UnderlyingType<L>::is_strict || UnderlyingType<R>::is_strict);
+      (UnderlyingType<L>::is_strict || UnderlyingType<R>::is_strict) &&
+      !(UnderlyingType<L>::is_checked || UnderlyingType<R>::is_checked) &&
+      !(UnderlyingType<L>::is_clamped || UnderlyingType<R>::is_clamped);
 };
 
 template <typename L, typename R>