diff --git a/BUILD.gn b/BUILD.gn
index de433af7e4..6d0ab72ad3 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -4065,6 +4065,7 @@ v8_component("v8_libbase") {
     "src/base/region-allocator.h",
     "src/base/ring-buffer.h",
     "src/base/safe_conversions.h",
+    "src/base/safe_conversions_arm_impl.h",
     "src/base/safe_conversions_impl.h",
     "src/base/small-vector.h",
     "src/base/sys-info.cc",
diff --git a/src/base/safe_conversions.h b/src/base/safe_conversions.h
index f63f1ad99e..38aa7b9aaa 100644
--- a/src/base/safe_conversions.h
+++ b/src/base/safe_conversions.h
@@ -4,59 +4,383 @@
 
 // Slightly adapted for inclusion in V8.
 // Copyright 2014 the V8 project authors. All rights reserved.
+// List of adaptations:
+// - include guard names
+// - wrap in v8 namespace
+// - formatting (git cl format)
+// - include paths
 
 #ifndef V8_BASE_SAFE_CONVERSIONS_H_
 #define V8_BASE_SAFE_CONVERSIONS_H_
 
+#include <stddef.h>
+
+#include <cmath>
 #include <limits>
+#include <type_traits>
 
 #include "src/base/safe_conversions_impl.h"
 
+#if defined(__ARMEL__) && !defined(__native_client__)
+#include "src/base/safe_conversions_arm_impl.h"
+#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (1)
+#else
+#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (0)
+#endif
+
+#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
+#include <ostream>
+#endif
+
 namespace v8 {
 namespace base {
+namespace internal {
+
+#if !BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
+template <typename Dst, typename Src>
+struct SaturateFastAsmOp {
+  static constexpr bool is_supported = false;
+  static constexpr Dst Do(Src) {
+    // Force a compile failure if instantiated.
+    return CheckOnFailure::template HandleFailure<Dst>();
+  }
+};
+#endif  // BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
+#undef BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
+
+// The following special case a few specific integer conversions where we can
+// eke out better performance than range checking.
+template <typename Dst, typename Src, typename Enable = void>
+struct IsValueInRangeFastOp {
+  static constexpr bool is_supported = false;
+  static constexpr bool Do(Src value) {
+    // Force a compile failure if instantiated.
+    return CheckOnFailure::template HandleFailure<bool>();
+  }
+};
+
+// Signed to signed range comparison.
+template <typename Dst, typename Src>
+struct IsValueInRangeFastOp<
+    Dst, Src,
+    typename std::enable_if<
+        std::is_integral<Dst>::value && std::is_integral<Src>::value &&
+        std::is_signed<Dst>::value && std::is_signed<Src>::value &&
+        !IsTypeInRangeForNumericType<Dst, Src>::value>::type> {
+  static constexpr bool is_supported = true;
+
+  static constexpr bool Do(Src value) {
+    // Just downcast to the smaller type, sign extend it back to the original
+    // type, and then see if it matches the original value.
+    return value == static_cast<Dst>(value);
+  }
+};
+
+// Signed to unsigned range comparison.
+template <typename Dst, typename Src>
+struct IsValueInRangeFastOp<
+    Dst, Src,
+    typename std::enable_if<
+        std::is_integral<Dst>::value && std::is_integral<Src>::value &&
+        !std::is_signed<Dst>::value && std::is_signed<Src>::value &&
+        !IsTypeInRangeForNumericType<Dst, Src>::value>::type> {
+  static constexpr bool is_supported = true;
+
+  static constexpr bool Do(Src value) {
+    // We cast a signed as unsigned to overflow negative values to the top,
+    // then compare against whichever maximum is smaller, as our upper bound.
+    return as_unsigned(value) <= as_unsigned(CommonMax<Src, Dst>());
+  }
+};
 
 // 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) {
-  return internal::DstRangeRelationToSrcRange<Dst>(value) ==
-         internal::RANGE_VALID;
+constexpr bool IsValueInRangeForNumericType(Src value) {
+  using SrcType = typename internal::UnderlyingType<Src>::type;
+  return internal::IsValueInRangeFastOp<Dst, SrcType>::is_supported
+             ? internal::IsValueInRangeFastOp<Dst, SrcType>::Do(
+                   static_cast<SrcType>(value))
+             : internal::DstRangeRelationToSrcRange<Dst>(
+                   static_cast<SrcType>(value))
+                   .IsValid();
 }
 
 // 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);
+template <typename Dst, class CheckHandler = internal::CheckOnFailure,
+          typename Src>
+constexpr Dst checked_cast(Src value) {
+  // This throws a compile-time error on evaluating the constexpr if it can be
+  // determined at compile-time as failing, otherwise it will CHECK at runtime.
+  using SrcType = typename internal::UnderlyingType<Src>::type;
+  return BASE_NUMERICS_LIKELY((IsValueInRangeForNumericType<Dst>(value)))
+             ? static_cast<Dst>(static_cast<SrcType>(value))
+             : CheckHandler::template HandleFailure<Dst>();
 }
 
-// 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 trigger a CHECK condition.
+// Default boundaries for integral/float: max/infinity, lowest/-infinity, 0/NaN.
+// You may provide your own limits (e.g. to saturated_cast) so long as you
+// implement all of the static constexpr member functions in the class below.
+template <typename T>
+struct SaturationDefaultLimits : public std::numeric_limits<T> {
+  static constexpr T NaN() {
+    return std::numeric_limits<T>::has_quiet_NaN
+               ? std::numeric_limits<T>::quiet_NaN()
+               : T();
+  }
+  using std::numeric_limits<T>::max;
+  static constexpr T Overflow() {
+    return std::numeric_limits<T>::has_infinity
+               ? std::numeric_limits<T>::infinity()
+               : std::numeric_limits<T>::max();
+  }
+  using std::numeric_limits<T>::lowest;
+  static constexpr T Underflow() {
+    return std::numeric_limits<T>::has_infinity
+               ? std::numeric_limits<T>::infinity() * -1
+               : std::numeric_limits<T>::lowest();
+  }
+};
+
+template <typename Dst, template <typename> class S, typename Src>
+constexpr Dst saturated_cast_impl(Src value, RangeCheck constraint) {
+  // For some reason clang generates much better code when the branch is
+  // structured exactly this way, rather than a sequence of checks.
+  return !constraint.IsOverflowFlagSet()
+             ? (!constraint.IsUnderflowFlagSet() ? static_cast<Dst>(value)
+                                                 : S<Dst>::Underflow())
+             // Skip this check for integral Src, which cannot be NaN.
+             : (std::is_integral<Src>::value || !constraint.IsUnderflowFlagSet()
+                    ? S<Dst>::Overflow()
+                    : S<Dst>::NaN());
+}
+
+// We can reduce the number of conditions and get slightly better performance
+// for normal signed and unsigned integer ranges. And in the specific case of
+// Arm, we can use the optimized saturation instructions.
+template <typename Dst, typename Src, typename Enable = void>
+struct SaturateFastOp {
+  static constexpr bool is_supported = false;
+  static constexpr Dst Do(Src value) {
+    // Force a compile failure if instantiated.
+    return CheckOnFailure::template HandleFailure<Dst>();
+  }
+};
+
 template <typename Dst, typename Src>
-inline Dst saturated_cast(Src value) {
-  // Optimization for floating point values, which already saturate.
-  if (std::numeric_limits<Dst>::is_iec559)
-    return static_cast<Dst>(value);
+struct SaturateFastOp<
+    Dst, Src,
+    typename std::enable_if<std::is_integral<Src>::value &&
+                            std::is_integral<Dst>::value &&
+                            SaturateFastAsmOp<Dst, Src>::is_supported>::type> {
+  static constexpr bool is_supported = true;
+  static constexpr Dst Do(Src value) {
+    return SaturateFastAsmOp<Dst, Src>::Do(value);
+  }
+};
 
-  switch (internal::DstRangeRelationToSrcRange<Dst>(value)) {
-    case internal::RANGE_VALID:
-      return static_cast<Dst>(value);
+template <typename Dst, typename Src>
+struct SaturateFastOp<
+    Dst, Src,
+    typename std::enable_if<std::is_integral<Src>::value &&
+                            std::is_integral<Dst>::value &&
+                            !SaturateFastAsmOp<Dst, Src>::is_supported>::type> {
+  static constexpr bool is_supported = true;
+  static constexpr Dst Do(Src value) {
+    // The exact order of the following is structured to hit the correct
+    // optimization heuristics across compilers. Do not change without
+    // checking the emitted code.
+    const Dst saturated = CommonMaxOrMin<Dst, Src>(
+        IsMaxInRangeForNumericType<Dst, Src>() ||
+        (!IsMinInRangeForNumericType<Dst, Src>() && IsValueNegative(value)));
+    return BASE_NUMERICS_LIKELY(IsValueInRangeForNumericType<Dst>(value))
+               ? static_cast<Dst>(value)
+               : saturated;
+  }
+};
 
-    case internal::RANGE_UNDERFLOW:
-      return std::numeric_limits<Dst>::min();
+// saturated_cast<> is analogous to static_cast<> for numeric types, except
+// that the specified numeric conversion will saturate by default rather than
+// overflow or underflow, and NaN assignment to an integral will return 0.
+// All boundary condition behaviors can be overriden with a custom handler.
+template <typename Dst,
+          template <typename> class SaturationHandler = SaturationDefaultLimits,
+          typename Src>
+constexpr Dst saturated_cast(Src value) {
+  using SrcType = typename UnderlyingType<Src>::type;
+  return !IsCompileTimeConstant(value) &&
+                 SaturateFastOp<Dst, SrcType>::is_supported &&
+                 std::is_same<SaturationHandler<Dst>,
+                              SaturationDefaultLimits<Dst>>::value
+             ? SaturateFastOp<Dst, SrcType>::Do(static_cast<SrcType>(value))
+             : saturated_cast_impl<Dst, SaturationHandler, SrcType>(
+                   static_cast<SrcType>(value),
+                   DstRangeRelationToSrcRange<Dst, SaturationHandler, SrcType>(
+                       static_cast<SrcType>(value)));
+}
 
-    case internal::RANGE_OVERFLOW:
-      return std::numeric_limits<Dst>::max();
+// 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>
+constexpr Dst strict_cast(Src value) {
+  using SrcType = typename UnderlyingType<Src>::type;
+  static_assert(UnderlyingType<Src>::is_numeric, "Argument must be numeric.");
+  static_assert(std::is_arithmetic<Dst>::value, "Result must be numeric.");
 
-    // Should fail only on attempting to assign NaN to a saturated integer.
-    case internal::RANGE_INVALID:
-      UNREACHABLE();
+  // If you got here from a compiler error, it's because you tried to assign
+  // from a source type to a destination type that has insufficient range.
+  // The solution may be to change the destination type you're assigning to,
+  // and use one large enough to represent the source.
+  // Alternatively, you may be better served with the checked_cast<> or
+  // saturated_cast<> template functions for your particular use case.
+  static_assert(StaticDstRangeRelationToSrcRange<Dst, SrcType>::value ==
+                    NUMERIC_RANGE_CONTAINED,
+                "The source type is out of range for the destination type. "
+                "Please see strict_cast<> comments for more information.");
+
+  return static_cast<Dst>(static_cast<SrcType>(value));
+}
+
+// Some wrappers to statically check that a type is in range.
+template <typename Dst, typename Src, class Enable = void>
+struct IsNumericRangeContained {
+  static constexpr bool value = false;
+};
+
+template <typename Dst, typename Src>
+struct IsNumericRangeContained<
+    Dst, Src,
+    typename std::enable_if<ArithmeticOrUnderlyingEnum<Dst>::value &&
+                            ArithmeticOrUnderlyingEnum<Src>::value>::type> {
+  static constexpr bool value =
+      StaticDstRangeRelationToSrcRange<Dst, Src>::value ==
+      NUMERIC_RANGE_CONTAINED;
+};
+
+// 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 the actual value being assigned.
+template <typename T>
+class StrictNumeric {
+ public:
+  using type = T;
+
+  constexpr StrictNumeric() : value_(0) {}
+
+  // Copy constructor.
+  template <typename Src>
+  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>
+  constexpr StrictNumeric(Src value)  // NOLINT(runtime/explicit)
+      : value_(strict_cast<T>(value)) {}
+
+  // If you got here from a compiler error, it's because you tried to assign
+  // from a source type to a destination type that has insufficient range.
+  // The solution may be to change the destination type you're assigning to,
+  // and use one large enough to represent the source.
+  // If you're assigning from a CheckedNumeric<> class, you may be able to use
+  // the AssignIfValid() member function, specify a narrower destination type to
+  // the member value functions (e.g. val.template ValueOrDie<Dst>()), use one
+  // of the value helper functions (e.g. ValueOrDieForType<Dst>(val)).
+  // If you've encountered an _ambiguous overload_ you can use a static_cast<>
+  // to explicitly cast the result to the destination type.
+  // If none of that works, you may be better served with the checked_cast<> or
+  // saturated_cast<> template functions for your particular use case.
+  template <typename Dst, typename std::enable_if<IsNumericRangeContained<
+                              Dst, T>::value>::type* = nullptr>
+  constexpr operator Dst() const {
+    return static_cast<typename ArithmeticOrUnderlyingEnum<Dst>::type>(value_);
   }
 
-  UNREACHABLE();
+ private:
+  const T value_;
+};
+
+// Convience wrapper returns a StrictNumeric from the provided arithmetic type.
+template <typename T>
+constexpr StrictNumeric<typename UnderlyingType<T>::type> MakeStrictNum(
+    const T value) {
+  return value;
+}
+
+#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
+// Overload the ostream output operator to make logging work nicely.
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const StrictNumeric<T>& value) {
+  os << static_cast<T>(value);
+  return os;
+}
+#endif
+
+#define BASE_NUMERIC_COMPARISON_OPERATORS(CLASS, NAME, OP)              \
+  template <typename L, typename R,                                     \
+            typename std::enable_if<                                    \
+                internal::Is##CLASS##Op<L, R>::value>::type* = nullptr> \
+  constexpr bool operator OP(const L lhs, const R rhs) {                \
+    return SafeCompare<NAME, typename UnderlyingType<L>::type,          \
+                       typename UnderlyingType<R>::type>(lhs, rhs);     \
+  }
+
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLess, <)
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLessOrEqual, <=)
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreater, >)
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreaterOrEqual, >=)
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsEqual, ==)
+BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsNotEqual, !=)
+
+}  // namespace internal
+
+using internal::as_signed;
+using internal::as_unsigned;
+using internal::checked_cast;
+using internal::IsTypeInRangeForNumericType;
+using internal::IsValueInRangeForNumericType;
+using internal::IsValueNegative;
+using internal::MakeStrictNum;
+using internal::SafeUnsignedAbs;
+using internal::saturated_cast;
+using internal::strict_cast;
+using internal::StrictNumeric;
+
+// Explicitly make a shorter size_t alias for convenience.
+using SizeT = StrictNumeric<size_t>;
+
+// floating -> integral conversions that saturate and thus can actually return
+// an integral type.  In most cases, these should be preferred over the std::
+// versions.
+template <typename Dst = int, typename Src,
+          typename = std::enable_if_t<std::is_integral<Dst>::value &&
+                                      std::is_floating_point<Src>::value>>
+Dst ClampFloor(Src value) {
+  return saturated_cast<Dst>(std::floor(value));
+}
+template <typename Dst = int, typename Src,
+          typename = std::enable_if_t<std::is_integral<Dst>::value &&
+                                      std::is_floating_point<Src>::value>>
+Dst ClampCeil(Src value) {
+  return saturated_cast<Dst>(std::ceil(value));
+}
+template <typename Dst = int, typename Src,
+          typename = std::enable_if_t<std::is_integral<Dst>::value &&
+                                      std::is_floating_point<Src>::value>>
+Dst ClampRound(Src value) {
+  const Src rounded =
+      (value >= 0.0f) ? std::floor(value + 0.5f) : std::ceil(value - 0.5f);
+  return saturated_cast<Dst>(rounded);
 }
 
 }  // namespace base
diff --git a/src/base/safe_conversions_arm_impl.h b/src/base/safe_conversions_arm_impl.h
new file mode 100644
index 0000000000..0e08a14405
--- /dev/null
+++ b/src/base/safe_conversions_arm_impl.h
@@ -0,0 +1,60 @@
+// Copyright 2017 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.
+
+// Slightly adapted for inclusion in V8.
+// Copyright 2014 the V8 project authors. All rights reserved.
+// List of adaptations:
+// - include guard names
+// - wrap in v8 namespace
+// - include paths
+
+#ifndef V8_BASE_SAFE_CONVERSIONS_ARM_IMPL_H_
+#define V8_BASE_SAFE_CONVERSIONS_ARM_IMPL_H_
+
+#include <cassert>
+#include <limits>
+#include <type_traits>
+
+#include "src/base/safe_conversions_impl.h"
+
+namespace v8 {
+namespace base {
+namespace internal {
+
+// Fast saturation to a destination type.
+template <typename Dst, typename Src>
+struct SaturateFastAsmOp {
+  static constexpr bool is_supported =
+      std::is_signed<Src>::value && std::is_integral<Dst>::value &&
+      std::is_integral<Src>::value &&
+      IntegerBitsPlusSign<Src>::value <= IntegerBitsPlusSign<int32_t>::value &&
+      IntegerBitsPlusSign<Dst>::value <= IntegerBitsPlusSign<int32_t>::value &&
+      !IsTypeInRangeForNumericType<Dst, Src>::value;
+
+  __attribute__((always_inline)) static Dst Do(Src value) {
+    int32_t src = value;
+    typename std::conditional<std::is_signed<Dst>::value, int32_t,
+                              uint32_t>::type result;
+    if (std::is_signed<Dst>::value) {
+      asm("ssat %[dst], %[shift], %[src]"
+          : [dst] "=r"(result)
+          : [src] "r"(src), [shift] "n"(IntegerBitsPlusSign<Dst>::value <= 32
+                                            ? IntegerBitsPlusSign<Dst>::value
+                                            : 32));
+    } else {
+      asm("usat %[dst], %[shift], %[src]"
+          : [dst] "=r"(result)
+          : [src] "r"(src), [shift] "n"(IntegerBitsPlusSign<Dst>::value < 32
+                                            ? IntegerBitsPlusSign<Dst>::value
+                                            : 31));
+    }
+    return static_cast<Dst>(result);
+  }
+};
+
+}  // namespace internal
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_SAFE_CONVERSIONS_ARM_IMPL_H_
diff --git a/src/base/safe_conversions_impl.h b/src/base/safe_conversions_impl.h
index 90c8e19353..7eebff2cd1 100644
--- a/src/base/safe_conversions_impl.h
+++ b/src/base/safe_conversions_impl.h
@@ -4,28 +4,130 @@
 
 // Slightly adapted for inclusion in V8.
 // Copyright 2014 the V8 project authors. All rights reserved.
+// List of adaptations:
+// - include guard names
+// - wrap in v8 namespace
+// - formatting (git cl format)
 
 #ifndef V8_BASE_SAFE_CONVERSIONS_IMPL_H_
 #define V8_BASE_SAFE_CONVERSIONS_IMPL_H_
 
-#include <limits>
+#include <stdint.h>
 
-#include "src/base/logging.h"
-#include "src/base/macros.h"
+#include <limits>
+#include <type_traits>
+
+#if defined(__GNUC__) || defined(__clang__)
+#define BASE_NUMERICS_LIKELY(x) __builtin_expect(!!(x), 1)
+#define BASE_NUMERICS_UNLIKELY(x) __builtin_expect(!!(x), 0)
+#else
+#define BASE_NUMERICS_LIKELY(x) (x)
+#define BASE_NUMERICS_UNLIKELY(x) (x)
+#endif
 
 namespace v8 {
 namespace base {
 namespace internal {
 
 // The std library doesn't provide a binary max_exponent for integers, however
-// we can compute one by adding one to the number of non-sign bits. This allows
-// for accurate range comparisons between floating point and integer types.
+// we can compute an analog using std::numeric_limits<>::digits.
 template <typename NumericType>
 struct MaxExponent {
-  static const int value = std::numeric_limits<NumericType>::is_iec559
+  static const int value = std::is_floating_point<NumericType>::value
                                ? std::numeric_limits<NumericType>::max_exponent
-                               : (sizeof(NumericType) * 8 + 1 -
-                                  std::numeric_limits<NumericType>::is_signed);
+                               : std::numeric_limits<NumericType>::digits + 1;
+};
+
+// The number of bits (including the sign) in an integer. Eliminates sizeof
+// hacks.
+template <typename NumericType>
+struct IntegerBitsPlusSign {
+  static const int value = std::numeric_limits<NumericType>::digits +
+                           std::is_signed<NumericType>::value;
+};
+
+// Helper templates for integer manipulations.
+
+template <typename Integer>
+struct PositionOfSignBit {
+  static const size_t value = IntegerBitsPlusSign<Integer>::value - 1;
+};
+
+// Determines if a numeric value is negative without throwing compiler
+// warnings on: unsigned(value) < 0.
+template <typename T,
+          typename std::enable_if<std::is_signed<T>::value>::type* = nullptr>
+constexpr bool IsValueNegative(T value) {
+  static_assert(std::is_arithmetic<T>::value, "Argument must be numeric.");
+  return value < 0;
+}
+
+template <typename T,
+          typename std::enable_if<!std::is_signed<T>::value>::type* = nullptr>
+constexpr bool IsValueNegative(T) {
+  static_assert(std::is_arithmetic<T>::value, "Argument must be numeric.");
+  return false;
+}
+
+// This performs a fast negation, returning a signed value. It works on unsigned
+// arguments, but probably doesn't do what you want for any unsigned value
+// larger than max / 2 + 1 (i.e. signed min cast to unsigned).
+template <typename T>
+constexpr typename std::make_signed<T>::type ConditionalNegate(
+    T x, bool is_negative) {
+  static_assert(std::is_integral<T>::value, "Type must be integral");
+  using SignedT = typename std::make_signed<T>::type;
+  using UnsignedT = typename std::make_unsigned<T>::type;
+  return static_cast<SignedT>(
+      (static_cast<UnsignedT>(x) ^ -SignedT(is_negative)) + is_negative);
+}
+
+// This performs a safe, absolute value via unsigned overflow.
+template <typename T>
+constexpr typename std::make_unsigned<T>::type SafeUnsignedAbs(T value) {
+  static_assert(std::is_integral<T>::value, "Type must be integral");
+  using UnsignedT = typename std::make_unsigned<T>::type;
+  return IsValueNegative(value)
+             ? static_cast<UnsignedT>(0u - static_cast<UnsignedT>(value))
+             : static_cast<UnsignedT>(value);
+}
+
+// This allows us to switch paths on known compile-time constants.
+#if defined(__clang__) || defined(__GNUC__)
+constexpr bool CanDetectCompileTimeConstant() { return true; }
+template <typename T>
+constexpr bool IsCompileTimeConstant(const T v) {
+  return __builtin_constant_p(v);
+}
+#else
+constexpr bool CanDetectCompileTimeConstant() { return false; }
+template <typename T>
+constexpr bool IsCompileTimeConstant(const T) {
+  return false;
+}
+#endif
+template <typename T>
+constexpr bool MustTreatAsConstexpr(const T v) {
+  // Either we can't detect a compile-time constant, and must always use the
+  // constexpr path, or we know we have a compile-time constant.
+  return !CanDetectCompileTimeConstant() || IsCompileTimeConstant(v);
+}
+
+// Forces a crash, like a CHECK(false). Used for numeric boundary errors.
+// Also used in a constexpr template to trigger a compilation failure on
+// an error condition.
+struct CheckOnFailure {
+  template <typename T>
+  static T HandleFailure() {
+#if defined(_MSC_VER)
+    __debugbreak();
+#elif defined(__GNUC__) || defined(__clang__)
+    __builtin_trap();
+#else
+    ((void)(*(volatile char*)0 = 0));
+#endif
+    return T();
+  }
 };
 
 enum IntegerRepresentation {
@@ -35,7 +137,7 @@ enum IntegerRepresentation {
 
 // A range for a given nunmeric Src type is contained for a given numeric Dst
 // type if both numeric_limits<Src>::max() <= numeric_limits<Dst>::max() and
-// numeric_limits<Src>::min() >= numeric_limits<Dst>::min() are true.
+// numeric_limits<Src>::lowest() >= numeric_limits<Dst>::lowest() are true.
 // We implement this as template specializations rather than simple static
 // comparisons to ensure type correctness in our comparisons.
 enum NumericRangeRepresentation {
@@ -46,16 +148,13 @@ enum NumericRangeRepresentation {
 // Helper templates to statically determine if our destination type can contain
 // maximum and minimum values represented by the source type.
 
-template <
-    typename Dst,
-    typename Src,
-    IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
-                                            ? INTEGER_REPRESENTATION_SIGNED
-                                            : INTEGER_REPRESENTATION_UNSIGNED,
-    IntegerRepresentation SrcSign =
-        std::numeric_limits<Src>::is_signed
-            ? INTEGER_REPRESENTATION_SIGNED
-            : INTEGER_REPRESENTATION_UNSIGNED >
+template <typename Dst, typename Src,
+          IntegerRepresentation DstSign = std::is_signed<Dst>::value
+                                              ? INTEGER_REPRESENTATION_SIGNED
+                                              : INTEGER_REPRESENTATION_UNSIGNED,
+          IntegerRepresentation SrcSign = std::is_signed<Src>::value
+                                              ? INTEGER_REPRESENTATION_SIGNED
+                                              : INTEGER_REPRESENTATION_UNSIGNED>
 struct StaticDstRangeRelationToSrcRange;
 
 // Same sign: Dst is guaranteed to contain Src only if its range is equal or
@@ -90,127 +189,622 @@ struct StaticDstRangeRelationToSrcRange<Dst,
   static const NumericRangeRepresentation value = NUMERIC_RANGE_NOT_CONTAINED;
 };
 
-enum RangeConstraint {
-  RANGE_VALID = 0x0,  // Value can be represented by the destination type.
-  RANGE_UNDERFLOW = 0x1,  // Value would overflow.
-  RANGE_OVERFLOW = 0x2,  // Value would underflow.
-  RANGE_INVALID = RANGE_UNDERFLOW | RANGE_OVERFLOW  // Invalid (i.e. NaN).
+// This class wraps the range constraints as separate booleans so the compiler
+// can identify constants and eliminate unused code paths.
+class RangeCheck {
+ public:
+  constexpr RangeCheck(bool is_in_lower_bound, bool is_in_upper_bound)
+      : is_underflow_(!is_in_lower_bound), is_overflow_(!is_in_upper_bound) {}
+  constexpr RangeCheck() : is_underflow_(0), is_overflow_(0) {}
+  constexpr bool IsValid() const { return !is_overflow_ && !is_underflow_; }
+  constexpr bool IsInvalid() const { return is_overflow_ && is_underflow_; }
+  constexpr bool IsOverflow() const { return is_overflow_ && !is_underflow_; }
+  constexpr bool IsUnderflow() const { return !is_overflow_ && is_underflow_; }
+  constexpr bool IsOverflowFlagSet() const { return is_overflow_; }
+  constexpr bool IsUnderflowFlagSet() const { return is_underflow_; }
+  constexpr bool operator==(const RangeCheck rhs) const {
+    return is_underflow_ == rhs.is_underflow_ &&
+           is_overflow_ == rhs.is_overflow_;
+  }
+  constexpr bool operator!=(const RangeCheck rhs) const {
+    return !(*this == rhs);
+  }
+
+ private:
+  // Do not change the order of these member variables. The integral conversion
+  // optimization depends on this exact order.
+  const bool is_underflow_;
+  const bool is_overflow_;
 };
 
-// Helper function for coercing an int back to a RangeContraint.
-inline RangeConstraint GetRangeConstraint(int integer_range_constraint) {
-  DCHECK(integer_range_constraint >= RANGE_VALID &&
-         integer_range_constraint <= RANGE_INVALID);
-  return static_cast<RangeConstraint>(integer_range_constraint);
-}
+// The following helper template addresses a corner case in range checks for
+// conversion from a floating-point type to an integral type of smaller range
+// but larger precision (e.g. float -> unsigned). The problem is as follows:
+//   1. Integral maximum is always one less than a power of two, so it must be
+//      truncated to fit the mantissa of the floating point. The direction of
+//      rounding is implementation defined, but by default it's always IEEE
+//      floats, which round to nearest and thus result in a value of larger
+//      magnitude than the integral value.
+//      Example: float f = UINT_MAX; // f is 4294967296f but UINT_MAX
+//                                   // is 4294967295u.
+//   2. If the floating point value is equal to the promoted integral maximum
+//      value, a range check will erroneously pass.
+//      Example: (4294967296f <= 4294967295u) // This is true due to a precision
+//                                            // loss in rounding up to float.
+//   3. When the floating point value is then converted to an integral, the
+//      resulting value is out of range for the target integral type and
+//      thus is implementation defined.
+//      Example: unsigned u = (float)INT_MAX; // u will typically overflow to 0.
+// To fix this bug we manually truncate the maximum value when the destination
+// type is an integral of larger precision than the source floating-point type,
+// such that the resulting maximum is represented exactly as a floating point.
+template <typename Dst, typename Src, template <typename> class Bounds>
+struct NarrowingRange {
+  using SrcLimits = std::numeric_limits<Src>;
+  using DstLimits = typename std::numeric_limits<Dst>;
 
-// This function creates a RangeConstraint from an upper and lower bound
-// check by taking advantage of the fact that only NaN can be out of range in
-// both directions at once.
-inline RangeConstraint GetRangeConstraint(bool is_in_upper_bound,
-                                   bool is_in_lower_bound) {
-  return GetRangeConstraint((is_in_upper_bound ? 0 : RANGE_OVERFLOW) |
-                            (is_in_lower_bound ? 0 : RANGE_UNDERFLOW));
-}
+  // Computes the mask required to make an accurate comparison between types.
+  static const int kShift =
+      (MaxExponent<Src>::value > MaxExponent<Dst>::value &&
+       SrcLimits::digits < DstLimits::digits)
+          ? (DstLimits::digits - SrcLimits::digits)
+          : 0;
+  template <typename T, typename std::enable_if<
+                            std::is_integral<T>::value>::type* = nullptr>
 
-template <
-    typename Dst,
-    typename Src,
-    IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
-                                            ? INTEGER_REPRESENTATION_SIGNED
-                                            : INTEGER_REPRESENTATION_UNSIGNED,
-    IntegerRepresentation SrcSign = std::numeric_limits<Src>::is_signed
-                                            ? INTEGER_REPRESENTATION_SIGNED
-                                            : INTEGER_REPRESENTATION_UNSIGNED,
-    NumericRangeRepresentation DstRange =
-        StaticDstRangeRelationToSrcRange<Dst, Src>::value >
+  // Masks out the integer bits that are beyond the precision of the
+  // intermediate type used for comparison.
+  static constexpr T Adjust(T value) {
+    static_assert(std::is_same<T, Dst>::value, "");
+    static_assert(kShift < DstLimits::digits, "");
+    return static_cast<T>(
+        ConditionalNegate(SafeUnsignedAbs(value) & ~((T(1) << kShift) - T(1)),
+                          IsValueNegative(value)));
+  }
+
+  template <typename T, typename std::enable_if<
+                            std::is_floating_point<T>::value>::type* = nullptr>
+  static constexpr T Adjust(T value) {
+    static_assert(std::is_same<T, Dst>::value, "");
+    static_assert(kShift == 0, "");
+    return value;
+  }
+
+  static constexpr Dst max() { return Adjust(Bounds<Dst>::max()); }
+  static constexpr Dst lowest() { return Adjust(Bounds<Dst>::lowest()); }
+};
+
+template <typename Dst, typename Src, template <typename> class Bounds,
+          IntegerRepresentation DstSign = std::is_signed<Dst>::value
+                                              ? INTEGER_REPRESENTATION_SIGNED
+                                              : INTEGER_REPRESENTATION_UNSIGNED,
+          IntegerRepresentation SrcSign = std::is_signed<Src>::value
+                                              ? INTEGER_REPRESENTATION_SIGNED
+                                              : INTEGER_REPRESENTATION_UNSIGNED,
+          NumericRangeRepresentation DstRange =
+              StaticDstRangeRelationToSrcRange<Dst, Src>::value>
 struct DstRangeRelationToSrcRangeImpl;
 
 // The following templates are for ranges that must be verified at runtime. We
 // split it into checks based on signedness to avoid confusing casts and
 // compiler warnings on signed an unsigned comparisons.
 
-// Dst range is statically determined to contain Src: Nothing to check.
-template <typename Dst,
-          typename Src,
-          IntegerRepresentation DstSign,
-          IntegerRepresentation SrcSign>
-struct DstRangeRelationToSrcRangeImpl<Dst,
-                                      Src,
-                                      DstSign,
-                                      SrcSign,
+// Same sign narrowing: The range is contained for normal limits.
+template <typename Dst, typename Src, template <typename> class Bounds,
+          IntegerRepresentation DstSign, IntegerRepresentation SrcSign>
+struct DstRangeRelationToSrcRangeImpl<Dst, Src, Bounds, DstSign, SrcSign,
                                       NUMERIC_RANGE_CONTAINED> {
-  static RangeConstraint Check(Src value) { return RANGE_VALID; }
+  static constexpr RangeCheck Check(Src value) {
+    using SrcLimits = std::numeric_limits<Src>;
+    using DstLimits = NarrowingRange<Dst, Src, Bounds>;
+    return RangeCheck(
+        static_cast<Dst>(SrcLimits::lowest()) >= DstLimits::lowest() ||
+            static_cast<Dst>(value) >= DstLimits::lowest(),
+        static_cast<Dst>(SrcLimits::max()) <= DstLimits::max() ||
+            static_cast<Dst>(value) <= DstLimits::max());
+  }
 };
 
 // Signed to signed narrowing: Both the upper and lower boundaries may be
-// exceeded.
-template <typename Dst, typename Src>
-struct DstRangeRelationToSrcRangeImpl<Dst,
-                                      Src,
-                                      INTEGER_REPRESENTATION_SIGNED,
-                                      INTEGER_REPRESENTATION_SIGNED,
-                                      NUMERIC_RANGE_NOT_CONTAINED> {
-  static RangeConstraint Check(Src value) {
-    return std::numeric_limits<Dst>::is_iec559
-               ? GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
-                                    value >= -std::numeric_limits<Dst>::max())
-               : GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
-                                    value >= std::numeric_limits<Dst>::min());
+// exceeded for standard limits.
+template <typename Dst, typename Src, template <typename> class Bounds>
+struct DstRangeRelationToSrcRangeImpl<
+    Dst, Src, Bounds, INTEGER_REPRESENTATION_SIGNED,
+    INTEGER_REPRESENTATION_SIGNED, NUMERIC_RANGE_NOT_CONTAINED> {
+  static constexpr RangeCheck Check(Src value) {
+    using DstLimits = NarrowingRange<Dst, Src, Bounds>;
+    return RangeCheck(value >= DstLimits::lowest(), value <= DstLimits::max());
   }
 };
 
-// Unsigned to unsigned narrowing: Only the upper boundary can be exceeded.
-template <typename Dst, typename Src>
-struct DstRangeRelationToSrcRangeImpl<Dst,
-                                      Src,
-                                      INTEGER_REPRESENTATION_UNSIGNED,
-                                      INTEGER_REPRESENTATION_UNSIGNED,
-                                      NUMERIC_RANGE_NOT_CONTAINED> {
-  static RangeConstraint Check(Src value) {
-    return GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), true);
+// Unsigned to unsigned narrowing: Only the upper bound can be exceeded for
+// standard limits.
+template <typename Dst, typename Src, template <typename> class Bounds>
+struct DstRangeRelationToSrcRangeImpl<
+    Dst, Src, Bounds, INTEGER_REPRESENTATION_UNSIGNED,
+    INTEGER_REPRESENTATION_UNSIGNED, NUMERIC_RANGE_NOT_CONTAINED> {
+  static constexpr RangeCheck Check(Src value) {
+    using DstLimits = NarrowingRange<Dst, Src, Bounds>;
+    return RangeCheck(
+        DstLimits::lowest() == Dst(0) || value >= DstLimits::lowest(),
+        value <= DstLimits::max());
   }
 };
 
-// Unsigned to signed: The upper boundary may be exceeded.
-template <typename Dst, typename Src>
-struct DstRangeRelationToSrcRangeImpl<Dst,
-                                      Src,
-                                      INTEGER_REPRESENTATION_SIGNED,
-                                      INTEGER_REPRESENTATION_UNSIGNED,
-                                      NUMERIC_RANGE_NOT_CONTAINED> {
-  static RangeConstraint Check(Src value) {
-    return sizeof(Dst) > sizeof(Src)
-               ? RANGE_VALID
-               : GetRangeConstraint(
-                     value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
-                     true);
+// Unsigned to signed: Only the upper bound can be exceeded for standard limits.
+template <typename Dst, typename Src, template <typename> class Bounds>
+struct DstRangeRelationToSrcRangeImpl<
+    Dst, Src, Bounds, INTEGER_REPRESENTATION_SIGNED,
+    INTEGER_REPRESENTATION_UNSIGNED, NUMERIC_RANGE_NOT_CONTAINED> {
+  static constexpr RangeCheck Check(Src value) {
+    using DstLimits = NarrowingRange<Dst, Src, Bounds>;
+    using Promotion = decltype(Src() + Dst());
+    return RangeCheck(DstLimits::lowest() <= Dst(0) ||
+                          static_cast<Promotion>(value) >=
+                              static_cast<Promotion>(DstLimits::lowest()),
+                      static_cast<Promotion>(value) <=
+                          static_cast<Promotion>(DstLimits::max()));
   }
 };
 
 // Signed to unsigned: The upper boundary may be exceeded for a narrower Dst,
-// and any negative value exceeds the lower boundary.
-template <typename Dst, typename Src>
-struct DstRangeRelationToSrcRangeImpl<Dst,
-                                      Src,
-                                      INTEGER_REPRESENTATION_UNSIGNED,
-                                      INTEGER_REPRESENTATION_SIGNED,
-                                      NUMERIC_RANGE_NOT_CONTAINED> {
-  static RangeConstraint Check(Src value) {
-    return (MaxExponent<Dst>::value >= MaxExponent<Src>::value)
-               ? GetRangeConstraint(true, value >= static_cast<Src>(0))
-               : GetRangeConstraint(
-                     value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
-                     value >= static_cast<Src>(0));
+// and any negative value exceeds the lower boundary for standard limits.
+template <typename Dst, typename Src, template <typename> class Bounds>
+struct DstRangeRelationToSrcRangeImpl<
+    Dst, Src, Bounds, INTEGER_REPRESENTATION_UNSIGNED,
+    INTEGER_REPRESENTATION_SIGNED, NUMERIC_RANGE_NOT_CONTAINED> {
+  static constexpr RangeCheck Check(Src value) {
+    using SrcLimits = std::numeric_limits<Src>;
+    using DstLimits = NarrowingRange<Dst, Src, Bounds>;
+    using Promotion = decltype(Src() + Dst());
+    return RangeCheck(
+        value >= Src(0) && (DstLimits::lowest() == 0 ||
+                            static_cast<Dst>(value) >= DstLimits::lowest()),
+        static_cast<Promotion>(SrcLimits::max()) <=
+                static_cast<Promotion>(DstLimits::max()) ||
+            static_cast<Promotion>(value) <=
+                static_cast<Promotion>(DstLimits::max()));
   }
 };
 
+// Simple wrapper for statically checking if a type's range is contained.
 template <typename Dst, typename Src>
-inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
-  // Both source and destination must be numeric.
-  STATIC_ASSERT(std::numeric_limits<Src>::is_specialized);
-  STATIC_ASSERT(std::numeric_limits<Dst>::is_specialized);
-  return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
+struct IsTypeInRangeForNumericType {
+  static const bool value = StaticDstRangeRelationToSrcRange<Dst, Src>::value ==
+                            NUMERIC_RANGE_CONTAINED;
+};
+
+template <typename Dst, template <typename> class Bounds = std::numeric_limits,
+          typename Src>
+constexpr RangeCheck DstRangeRelationToSrcRange(Src value) {
+  static_assert(std::is_arithmetic<Src>::value, "Argument must be numeric.");
+  static_assert(std::is_arithmetic<Dst>::value, "Result must be numeric.");
+  static_assert(Bounds<Dst>::lowest() < Bounds<Dst>::max(), "");
+  return DstRangeRelationToSrcRangeImpl<Dst, Src, Bounds>::Check(value);
+}
+
+// Integer promotion templates used by the portable checked integer arithmetic.
+template <size_t Size, bool IsSigned>
+struct IntegerForDigitsAndSign;
+
+#define INTEGER_FOR_DIGITS_AND_SIGN(I)                          \
+  template <>                                                   \
+  struct IntegerForDigitsAndSign<IntegerBitsPlusSign<I>::value, \
+                                 std::is_signed<I>::value> {    \
+    using type = I;                                             \
+  }
+
+INTEGER_FOR_DIGITS_AND_SIGN(int8_t);
+INTEGER_FOR_DIGITS_AND_SIGN(uint8_t);
+INTEGER_FOR_DIGITS_AND_SIGN(int16_t);
+INTEGER_FOR_DIGITS_AND_SIGN(uint16_t);
+INTEGER_FOR_DIGITS_AND_SIGN(int32_t);
+INTEGER_FOR_DIGITS_AND_SIGN(uint32_t);
+INTEGER_FOR_DIGITS_AND_SIGN(int64_t);
+INTEGER_FOR_DIGITS_AND_SIGN(uint64_t);
+#undef INTEGER_FOR_DIGITS_AND_SIGN
+
+// WARNING: We have no IntegerForSizeAndSign<16, *>. If we ever add one to
+// support 128-bit math, then the ArithmeticPromotion template below will need
+// to be updated (or more likely replaced with a decltype expression).
+static_assert(IntegerBitsPlusSign<intmax_t>::value == 64,
+              "Max integer size not supported for this toolchain.");
+
+template <typename Integer, bool IsSigned = std::is_signed<Integer>::value>
+struct TwiceWiderInteger {
+  using type =
+      typename IntegerForDigitsAndSign<IntegerBitsPlusSign<Integer>::value * 2,
+                                       IsSigned>::type;
+};
+
+enum ArithmeticPromotionCategory {
+  LEFT_PROMOTION,  // Use the type of the left-hand argument.
+  RIGHT_PROMOTION  // Use the type of the right-hand argument.
+};
+
+// Determines the type that can represent the largest positive value.
+template <typename Lhs, typename Rhs,
+          ArithmeticPromotionCategory Promotion =
+              (MaxExponent<Lhs>::value > MaxExponent<Rhs>::value)
+                  ? LEFT_PROMOTION
+                  : RIGHT_PROMOTION>
+struct MaxExponentPromotion;
+
+template <typename Lhs, typename Rhs>
+struct MaxExponentPromotion<Lhs, Rhs, LEFT_PROMOTION> {
+  using type = Lhs;
+};
+
+template <typename Lhs, typename Rhs>
+struct MaxExponentPromotion<Lhs, Rhs, RIGHT_PROMOTION> {
+  using type = Rhs;
+};
+
+// Determines the type that can represent the lowest arithmetic value.
+template <typename Lhs, typename Rhs,
+          ArithmeticPromotionCategory Promotion =
+              std::is_signed<Lhs>::value
+                  ? (std::is_signed<Rhs>::value
+                         ? (MaxExponent<Lhs>::value > MaxExponent<Rhs>::value
+                                ? LEFT_PROMOTION
+                                : RIGHT_PROMOTION)
+                         : LEFT_PROMOTION)
+                  : (std::is_signed<Rhs>::value
+                         ? RIGHT_PROMOTION
+                         : (MaxExponent<Lhs>::value < MaxExponent<Rhs>::value
+                                ? LEFT_PROMOTION
+                                : RIGHT_PROMOTION))>
+struct LowestValuePromotion;
+
+template <typename Lhs, typename Rhs>
+struct LowestValuePromotion<Lhs, Rhs, LEFT_PROMOTION> {
+  using type = Lhs;
+};
+
+template <typename Lhs, typename Rhs>
+struct LowestValuePromotion<Lhs, Rhs, RIGHT_PROMOTION> {
+  using type = Rhs;
+};
+
+// Determines the type that is best able to represent an arithmetic result.
+template <
+    typename Lhs, typename Rhs = Lhs,
+    bool is_intmax_type =
+        std::is_integral<typename MaxExponentPromotion<Lhs, Rhs>::type>::value&&
+            IntegerBitsPlusSign<typename MaxExponentPromotion<Lhs, Rhs>::type>::
+                value == IntegerBitsPlusSign<intmax_t>::value,
+    bool is_max_exponent =
+        StaticDstRangeRelationToSrcRange<
+            typename MaxExponentPromotion<Lhs, Rhs>::type, Lhs>::value ==
+        NUMERIC_RANGE_CONTAINED&& StaticDstRangeRelationToSrcRange<
+            typename MaxExponentPromotion<Lhs, Rhs>::type, Rhs>::value ==
+        NUMERIC_RANGE_CONTAINED>
+struct BigEnoughPromotion;
+
+// The side with the max exponent is big enough.
+template <typename Lhs, typename Rhs, bool is_intmax_type>
+struct BigEnoughPromotion<Lhs, Rhs, is_intmax_type, true> {
+  using type = typename MaxExponentPromotion<Lhs, Rhs>::type;
+  static const bool is_contained = true;
+};
+
+// We can use a twice wider type to fit.
+template <typename Lhs, typename Rhs>
+struct BigEnoughPromotion<Lhs, Rhs, false, false> {
+  using type =
+      typename TwiceWiderInteger<typename MaxExponentPromotion<Lhs, Rhs>::type,
+                                 std::is_signed<Lhs>::value ||
+                                     std::is_signed<Rhs>::value>::type;
+  static const bool is_contained = true;
+};
+
+// No type is large enough.
+template <typename Lhs, typename Rhs>
+struct BigEnoughPromotion<Lhs, Rhs, true, false> {
+  using type = typename MaxExponentPromotion<Lhs, Rhs>::type;
+  static const bool is_contained = false;
+};
+
+// We can statically check if operations on the provided types can wrap, so we
+// can skip the checked operations if they're not needed. So, for an integer we
+// care if the destination type preserves the sign and is twice the width of
+// the source.
+template <typename T, typename Lhs, typename Rhs = Lhs>
+struct IsIntegerArithmeticSafe {
+  static const bool value =
+      !std::is_floating_point<T>::value &&
+      !std::is_floating_point<Lhs>::value &&
+      !std::is_floating_point<Rhs>::value &&
+      std::is_signed<T>::value >= std::is_signed<Lhs>::value &&
+      IntegerBitsPlusSign<T>::value >= (2 * IntegerBitsPlusSign<Lhs>::value) &&
+      std::is_signed<T>::value >= std::is_signed<Rhs>::value &&
+      IntegerBitsPlusSign<T>::value >= (2 * IntegerBitsPlusSign<Rhs>::value);
+};
+
+// Promotes to a type that can represent any possible result of a binary
+// arithmetic operation with the source types.
+template <typename Lhs, typename Rhs,
+          bool is_promotion_possible = IsIntegerArithmeticSafe<
+              typename std::conditional<std::is_signed<Lhs>::value ||
+                                            std::is_signed<Rhs>::value,
+                                        intmax_t, uintmax_t>::type,
+              typename MaxExponentPromotion<Lhs, Rhs>::type>::value>
+struct FastIntegerArithmeticPromotion;
+
+template <typename Lhs, typename Rhs>
+struct FastIntegerArithmeticPromotion<Lhs, Rhs, true> {
+  using type =
+      typename TwiceWiderInteger<typename MaxExponentPromotion<Lhs, Rhs>::type,
+                                 std::is_signed<Lhs>::value ||
+                                     std::is_signed<Rhs>::value>::type;
+  static_assert(IsIntegerArithmeticSafe<type, Lhs, Rhs>::value, "");
+  static const bool is_contained = true;
+};
+
+template <typename Lhs, typename Rhs>
+struct FastIntegerArithmeticPromotion<Lhs, Rhs, false> {
+  using type = typename BigEnoughPromotion<Lhs, Rhs>::type;
+  static const bool is_contained = false;
+};
+
+// Extracts the underlying type from an enum.
+template <typename T, bool is_enum = std::is_enum<T>::value>
+struct ArithmeticOrUnderlyingEnum;
+
+template <typename T>
+struct ArithmeticOrUnderlyingEnum<T, true> {
+  using type = typename std::underlying_type<T>::type;
+  static const bool value = std::is_arithmetic<type>::value;
+};
+
+template <typename T>
+struct ArithmeticOrUnderlyingEnum<T, false> {
+  using type = T;
+  static const bool value = std::is_arithmetic<type>::value;
+};
+
+// The following are helper templates used in the CheckedNumeric class.
+template <typename T>
+class CheckedNumeric;
+
+template <typename T>
+class ClampedNumeric;
+
+template <typename T>
+class StrictNumeric;
+
+// Used to treat CheckedNumeric and arithmetic underlying types the same.
+template <typename T>
+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;
+};
+
+template <typename T>
+struct UnderlyingType<CheckedNumeric<T>> {
+  using type = T;
+  static const bool is_numeric = true;
+  static const bool is_checked = true;
+  static const bool is_clamped = false;
+  static const bool is_strict = false;
+};
+
+template <typename T>
+struct UnderlyingType<ClampedNumeric<T>> {
+  using type = T;
+  static const bool is_numeric = true;
+  static const bool is_checked = false;
+  static const bool is_clamped = true;
+  static const bool is_strict = false;
+};
+
+template <typename T>
+struct UnderlyingType<StrictNumeric<T>> {
+  using type = T;
+  static const bool is_numeric = true;
+  static const bool is_checked = false;
+  static const bool is_clamped = false;
+  static const bool is_strict = true;
+};
+
+template <typename L, typename R>
+struct IsCheckedOp {
+  static const bool value =
+      UnderlyingType<L>::is_numeric && UnderlyingType<R>::is_numeric &&
+      (UnderlyingType<L>::is_checked || UnderlyingType<R>::is_checked);
+};
+
+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_checked || UnderlyingType<R>::is_checked);
+};
+
+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_checked || UnderlyingType<R>::is_checked) &&
+      !(UnderlyingType<L>::is_clamped || UnderlyingType<R>::is_clamped);
+};
+
+// as_signed<> returns the supplied integral value (or integral castable
+// Numeric template) cast as a signed integral of equivalent precision.
+// I.e. it's mostly an alias for: static_cast<std::make_signed<T>::type>(t)
+template <typename Src>
+constexpr typename std::make_signed<
+    typename base::internal::UnderlyingType<Src>::type>::type
+as_signed(const Src value) {
+  static_assert(std::is_integral<decltype(as_signed(value))>::value,
+                "Argument must be a signed or unsigned integer type.");
+  return static_cast<decltype(as_signed(value))>(value);
+}
+
+// as_unsigned<> returns the supplied integral value (or integral castable
+// Numeric template) cast as an unsigned integral of equivalent precision.
+// I.e. it's mostly an alias for: static_cast<std::make_unsigned<T>::type>(t)
+template <typename Src>
+constexpr typename std::make_unsigned<
+    typename base::internal::UnderlyingType<Src>::type>::type
+as_unsigned(const Src value) {
+  static_assert(std::is_integral<decltype(as_unsigned(value))>::value,
+                "Argument must be a signed or unsigned integer type.");
+  return static_cast<decltype(as_unsigned(value))>(value);
+}
+
+template <typename L, typename R>
+constexpr bool IsLessImpl(const L lhs, const R rhs, const RangeCheck l_range,
+                          const RangeCheck r_range) {
+  return l_range.IsUnderflow() || r_range.IsOverflow() ||
+         (l_range == r_range && static_cast<decltype(lhs + rhs)>(lhs) <
+                                    static_cast<decltype(lhs + rhs)>(rhs));
+}
+
+template <typename L, typename R>
+struct IsLess {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return IsLessImpl(lhs, rhs, DstRangeRelationToSrcRange<R>(lhs),
+                      DstRangeRelationToSrcRange<L>(rhs));
+  }
+};
+
+template <typename L, typename R>
+constexpr bool IsLessOrEqualImpl(const L lhs, const R rhs,
+                                 const RangeCheck l_range,
+                                 const RangeCheck r_range) {
+  return l_range.IsUnderflow() || r_range.IsOverflow() ||
+         (l_range == r_range && static_cast<decltype(lhs + rhs)>(lhs) <=
+                                    static_cast<decltype(lhs + rhs)>(rhs));
+}
+
+template <typename L, typename R>
+struct IsLessOrEqual {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return IsLessOrEqualImpl(lhs, rhs, DstRangeRelationToSrcRange<R>(lhs),
+                             DstRangeRelationToSrcRange<L>(rhs));
+  }
+};
+
+template <typename L, typename R>
+constexpr bool IsGreaterImpl(const L lhs, const R rhs, const RangeCheck l_range,
+                             const RangeCheck r_range) {
+  return l_range.IsOverflow() || r_range.IsUnderflow() ||
+         (l_range == r_range && static_cast<decltype(lhs + rhs)>(lhs) >
+                                    static_cast<decltype(lhs + rhs)>(rhs));
+}
+
+template <typename L, typename R>
+struct IsGreater {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return IsGreaterImpl(lhs, rhs, DstRangeRelationToSrcRange<R>(lhs),
+                         DstRangeRelationToSrcRange<L>(rhs));
+  }
+};
+
+template <typename L, typename R>
+constexpr bool IsGreaterOrEqualImpl(const L lhs, const R rhs,
+                                    const RangeCheck l_range,
+                                    const RangeCheck r_range) {
+  return l_range.IsOverflow() || r_range.IsUnderflow() ||
+         (l_range == r_range && static_cast<decltype(lhs + rhs)>(lhs) >=
+                                    static_cast<decltype(lhs + rhs)>(rhs));
+}
+
+template <typename L, typename R>
+struct IsGreaterOrEqual {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return IsGreaterOrEqualImpl(lhs, rhs, DstRangeRelationToSrcRange<R>(lhs),
+                                DstRangeRelationToSrcRange<L>(rhs));
+  }
+};
+
+template <typename L, typename R>
+struct IsEqual {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return DstRangeRelationToSrcRange<R>(lhs) ==
+               DstRangeRelationToSrcRange<L>(rhs) &&
+           static_cast<decltype(lhs + rhs)>(lhs) ==
+               static_cast<decltype(lhs + rhs)>(rhs);
+  }
+};
+
+template <typename L, typename R>
+struct IsNotEqual {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  static constexpr bool Test(const L lhs, const R rhs) {
+    return DstRangeRelationToSrcRange<R>(lhs) !=
+               DstRangeRelationToSrcRange<L>(rhs) ||
+           static_cast<decltype(lhs + rhs)>(lhs) !=
+               static_cast<decltype(lhs + rhs)>(rhs);
+  }
+};
+
+// These perform the actual math operations on the CheckedNumerics.
+// Binary arithmetic operations.
+template <template <typename, typename> class C, typename L, typename R>
+constexpr bool SafeCompare(const L lhs, const R rhs) {
+  static_assert(std::is_arithmetic<L>::value && std::is_arithmetic<R>::value,
+                "Types must be numeric.");
+  using Promotion = BigEnoughPromotion<L, R>;
+  using BigType = typename Promotion::type;
+  return Promotion::is_contained
+             // Force to a larger type for speed if both are contained.
+             ? C<BigType, BigType>::Test(
+                   static_cast<BigType>(static_cast<L>(lhs)),
+                   static_cast<BigType>(static_cast<R>(rhs)))
+             // Let the template functions figure it out for mixed types.
+             : C<L, R>::Test(lhs, rhs);
+}
+
+template <typename Dst, typename Src>
+constexpr bool IsMaxInRangeForNumericType() {
+  return IsGreaterOrEqual<Dst, Src>::Test(std::numeric_limits<Dst>::max(),
+                                          std::numeric_limits<Src>::max());
+}
+
+template <typename Dst, typename Src>
+constexpr bool IsMinInRangeForNumericType() {
+  return IsLessOrEqual<Dst, Src>::Test(std::numeric_limits<Dst>::lowest(),
+                                       std::numeric_limits<Src>::lowest());
+}
+
+template <typename Dst, typename Src>
+constexpr Dst CommonMax() {
+  return !IsMaxInRangeForNumericType<Dst, Src>()
+             ? Dst(std::numeric_limits<Dst>::max())
+             : Dst(std::numeric_limits<Src>::max());
+}
+
+template <typename Dst, typename Src>
+constexpr Dst CommonMin() {
+  return !IsMinInRangeForNumericType<Dst, Src>()
+             ? Dst(std::numeric_limits<Dst>::lowest())
+             : Dst(std::numeric_limits<Src>::lowest());
+}
+
+// This is a wrapper to generate return the max or min for a supplied type.
+// If the argument is false, the returned value is the maximum. If true the
+// returned value is the minimum.
+template <typename Dst, typename Src = Dst>
+constexpr Dst CommonMaxOrMin(bool is_min) {
+  return is_min ? CommonMin<Dst, Src>() : CommonMax<Dst, Src>();
 }
 
 }  // namespace internal