Convert CheckedNumeric unary operators to constexpr

base/numerics/safe_math.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_NUMERICS_SAFE_MATH_H_
 #define BASE_NUMERICS_SAFE_MATH_H_
 
 #include <stddef.h>
 
 #include <limits>
@@ skipping 186 matching lines @@
   CheckedNumeric& operator<<=(const Src rhs);
   template <typename Src>
   CheckedNumeric& operator>>=(const Src rhs);
   template <typename Src>
   CheckedNumeric& operator&=(const Src rhs);
   template <typename Src>
   CheckedNumeric& operator|=(const Src rhs);
   template <typename Src>
   CheckedNumeric& operator^=(const Src rhs);
 
-  CheckedNumeric operator-() const {
-    // Negation is always valid for floating point.
-    T value = 0;
-    bool is_valid = (std::is_floating_point<T>::value || IsValid()) &&
-                    CheckedNeg(state_.value(), &value);
-    return CheckedNumeric<T>(value, is_valid);
+  constexpr CheckedNumeric operator-() const {
+    return CheckedNumeric<T>(
+        NegateWrapper(state_.value()),
+        IsValid() &&
+            (!std::is_signed<T>::value || std::is_floating_point<T>::value ||
+             NegateWrapper(state_.value()) !=
+                 std::numeric_limits<T>::lowest()));
   }
 
-  CheckedNumeric operator~() const {
-    static_assert(!std::is_signed<T>::value, "Type must be unsigned.");
-    T value = 0;
-    bool is_valid = IsValid() && CheckedInv(state_.value(), &value);
-    return CheckedNumeric<T>(value, is_valid);
+  constexpr CheckedNumeric operator~() const {
+    return CheckedNumeric<decltype(InvertWrapper(T()))>(
+        InvertWrapper(state_.value()), IsValid());
   }
 
-  CheckedNumeric Abs() const {
-    // Absolute value is always valid for floating point.
-    T value = 0;
-    bool is_valid = (std::is_floating_point<T>::value || IsValid()) &&
-                    CheckedAbs(state_.value(), &value);
-    return CheckedNumeric<T>(value, is_valid);
+  constexpr CheckedNumeric Abs() const {
+    return CheckedNumeric<T>(
+        AbsWrapper(state_.value()),
+        IsValid() &&
+            (!std::is_signed<T>::value || std::is_floating_point<T>::value ||
+             AbsWrapper(state_.value()) != std::numeric_limits<T>::lowest()));
   }
 
   template <typename U>
   constexpr CheckedNumeric<typename MathWrapper<CheckedMaxOp, T, U>::type> Max(
       const U rhs) const {
     using R = typename UnderlyingType<U>::type;
     using result_type = typename MathWrapper<CheckedMaxOp, T, U>::type;
     // TODO(jschuh): This can be converted to the MathOp version and remain
     // constexpr once we have C++14 support.
     return CheckedNumeric<result_type>(
@@ skipping 262 matching lines @@
 using internal::CheckMod;
 using internal::CheckLsh;
 using internal::CheckRsh;
 using internal::CheckAnd;
 using internal::CheckOr;
 using internal::CheckXor;
 
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_MATH_H_