Convert base/numerics conversions to constexpr

base/numerics/safe_conversions.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_CONVERSIONS_H_
 #define BASE_NUMERICS_SAFE_CONVERSIONS_H_
 
 #include <stddef.h>
 
 #include <limits>
 #include <type_traits>
 
 #include "base/logging.h"
 #include "base/numerics/safe_conversions_impl.h"
 
 namespace base {
 
 // Convenience function that returns true if the supplied value is in range
 // for the destination type.
 template <typename Dst, typename Src>
-inline bool IsValueInRangeForNumericType(Src value) {
+inline constexpr bool IsValueInRangeForNumericType(Src value) {
   return internal::DstRangeRelationToSrcRange<Dst>(value) ==
          internal::RANGE_VALID;
 }
 
 // Convenience function for determining if a numeric value is negative without
 // throwing compiler warnings on: unsigned(value) < 0.
 template <typename T>
-typename std::enable_if<std::numeric_limits<T>::is_signed, bool>::type
+constexpr typename std::enable_if<std::numeric_limits<T>::is_signed, bool>::type
 IsValueNegative(T value) {
   static_assert(std::numeric_limits<T>::is_specialized,
                 "Argument must be numeric.");
   return value < 0;
 }
 
 template <typename T>
-typename std::enable_if<!std::numeric_limits<T>::is_signed, bool>::type
-    IsValueNegative(T) {
+constexpr typename std::enable_if<!std::numeric_limits<T>::is_signed,
+                                  bool>::type IsValueNegative(T) {
   static_assert(std::numeric_limits<T>::is_specialized,
                 "Argument must be numeric.");
   return false;
 }
 
 // checked_cast<> is analogous to static_cast<> for numeric types,
 // except that it CHECKs that the specified numeric conversion will not
 // overflow or underflow. NaN source will always trigger a CHECK.
 template <typename Dst, typename Src>
 inline Dst checked_cast(Src value) {
   CHECK(IsValueInRangeForNumericType<Dst>(value));
   return static_cast<Dst>(value);
 }
 
 // HandleNaN will cause this class to CHECK(false).
 struct SaturatedCastNaNBehaviorCheck {
   template <typename T>
   static T HandleNaN() {
     CHECK(false);
     return T();
   }
 };
 
 // HandleNaN will return 0 in this case.
 struct SaturatedCastNaNBehaviorReturnZero {
   template <typename T>
-  static T HandleNaN() {
+  static constexpr T HandleNaN() {
     return T();
   }
 };
 
 // saturated_cast<> is analogous to static_cast<> for numeric types, except
 // that the specified numeric conversion will saturate rather than overflow or
 // underflow. NaN assignment to an integral will defer the behavior to a
 // specified class. By default, it will return 0.
 template <typename Dst,
           class NaNHandler = SaturatedCastNaNBehaviorReturnZero,
@@ skipping 19 matching lines @@
   }
 
   NOTREACHED();
   return static_cast<Dst>(value);
 }
 
 // strict_cast<> is analogous to static_cast<> for numeric types, except that
 // it will cause a compile failure if the destination type is not large enough
 // to contain any value in the source type. It performs no runtime checking.
 template <typename Dst, typename Src>
-inline Dst strict_cast(Src value) {
+inline constexpr Dst strict_cast(Src value) {
   static_assert(std::numeric_limits<Src>::is_specialized,
                 "Argument must be numeric.");
   static_assert(std::numeric_limits<Dst>::is_specialized,
                 "Result must be numeric.");
   static_assert((internal::StaticDstRangeRelationToSrcRange<Dst, Src>::value ==
                  internal::NUMERIC_RANGE_CONTAINED),
                 "The numeric conversion is out of range for this type. You "
                 "should probably use one of the following conversion "
                 "mechanisms on the value you want to pass:\n"
                 "- base::checked_cast\n"
                 "- base::saturated_cast\n"
                 "- base::CheckedNumeric");
 
   return static_cast<Dst>(value);
 }
 
 // StrictNumeric implements compile time range checking between numeric types by
 // wrapping assignment operations in a strict_cast. This class is intended to be
 // used for function arguments and return types, to ensure the destination type
 // can always contain the source type. This is essentially the same as enforcing
 // -Wconversion in gcc and C4302 warnings on MSVC, but it can be applied
 // incrementally at API boundaries, making it easier to convert code so that it
 // compiles cleanly with truncation warnings enabled.
 // This template should introduce no runtime overhead, but it also provides no
 // runtime checking of any of the associated mathematical operations. Use
-// CheckedNumeric for runtime range checks of tha actual value being assigned.
+// CheckedNumeric for runtime range checks of the actual value being assigned.
 template <typename T>
 class StrictNumeric {
  public:
   typedef T type;
 
-  StrictNumeric() : value_(0) {}
+  constexpr StrictNumeric() : value_(0) {}
 
   // Copy constructor.
   template <typename Src>
-  StrictNumeric(const StrictNumeric<Src>& rhs)
+  constexpr StrictNumeric(const StrictNumeric<Src>& rhs)
       : value_(strict_cast<T>(rhs.value_)) {}
 
   // This is not an explicit constructor because we implicitly upgrade regular
   // numerics to StrictNumerics to make them easier to use.
   template <typename Src>
-  StrictNumeric(Src value)
+  constexpr StrictNumeric(Src value)
       : value_(strict_cast<T>(value)) {}
 
   // The numeric cast operator basically handles all the magic.
   template <typename Dst>
-  operator Dst() const {
+  constexpr operator Dst() const {
     return strict_cast<Dst>(value_);
   }
 
  private:
-  T value_;
+  const T value_;
 };
 
 // Explicitly make a shorter size_t typedef for convenience.
 typedef StrictNumeric<size_t> SizeT;
 
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_CONVERSIONS_H_