Split out code to be shared between CheckedNumeric and ClampedNumeric

BUG=672489

Review-Url: https://codereview.chromium.org/2931323002
Cr-Commit-Position: refs/heads/master@{#478803}

base/BUILD.gn

@@ -593,10 +593,12 @@ component("base") {
     "nix/mime_util_xdg.h",
     "nix/xdg_util.cc",
     "nix/xdg_util.h",
+    "numerics/checked_math.h",
+    "numerics/checked_math_impl.h",
     "numerics/safe_conversions.h",
     "numerics/safe_conversions_impl.h",
     "numerics/safe_math.h",
-    "numerics/safe_math_impl.h",
+    "numerics/safe_math_shared_impl.h",
     "numerics/saturated_arithmetic.h",
     "numerics/saturated_arithmetic_arm.h",
     "observer_list.h",

base/numerics/checked_math.h

+// 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.
+
+#ifndef BASE_NUMERICS_CHECKED_MATH_H_
+#define BASE_NUMERICS_CHECKED_MATH_H_
+
+#include <stddef.h>
+
+#include <limits>
+#include <type_traits>
+
+#include "base/numerics/checked_math_impl.h"
+
+namespace base {
+namespace internal {
+
+// CheckedNumeric<> implements all the logic and operators for detecting integer
+// boundary conditions such as overflow, underflow, and invalid conversions.
+// The CheckedNumeric type implicitly converts from floating point and integer
+// data types, and contains overloads for basic arithmetic operations (i.e.: +,
+// -, *, / for all types and %, <<, >>, &, |, ^ for integers). Type promotions
+// are a slightly modified version of the standard C arithmetic rules with the
+// two differences being that there is no default promotion to int and bitwise
+// logical operations always return an unsigned of the wider type.
+//
+// You may also use one of the variadic convenience functions, which accept
+// standard arithmetic or CheckedNumeric types, perform arithmetic operations,
+// and return a CheckedNumeric result. The supported functions are:
+//  CheckAdd() - Addition.
+//  CheckSub() - Subtraction.
+//  CheckMul() - Multiplication.
+//  CheckDiv() - Division.
+//  CheckMod() - Modulous (integer only).
+//  CheckLsh() - Left integer shift (integer only).
+//  CheckRsh() - Right integer shift (integer only).
+//  CheckAnd() - Bitwise AND (integer only with unsigned result).
+//  CheckOr()  - Bitwise OR (integer only with unsigned result).
+//  CheckXor() - Bitwise XOR (integer only with unsigned result).
+//  CheckMax() - Maximum of supplied arguments.
+//  CheckMin() - Minimum of supplied arguments.
+//
+// The unary negation, increment, and decrement operators are supported, along
+// with the following unary arithmetic methods, which return a new
+// CheckedNumeric as a result of the operation:
+//  Abs() - Absolute value.
+//  UnsignedAbs() - Absolute value as an equal-width unsigned underlying type
+//          (valid for only integral types).
+//  Max() - Returns whichever is greater of the current instance or argument.
+//          The underlying return type is whichever has the greatest magnitude.
+//  Min() - Returns whichever is lowest of the current instance or argument.
+//          The underlying return type is whichever has can represent the lowest
+//          number in the smallest width (e.g. int8_t over unsigned, int over
+//          int8_t, and float over int).
+//
+// The following methods convert from CheckedNumeric to standard numeric values:
+//  AssignIfValid() - Assigns the underlying value to the supplied destination
+//          pointer if the value is currently valid and within the range
+//          supported by the destination type. Returns true on success.
+//  ****************************************************************************
+//  *  WARNING: All of the following functions return a StrictNumeric, which   *
+//  *  is valid for comparison and assignment operations, but will trigger a   *
+//  *  compile failure on attempts to assign to a type of insufficient range.  *
+//  ****************************************************************************
+//  IsValid() - Returns true if the underlying numeric value is valid (i.e. has
+//          has not wrapped and is not the result of an invalid conversion).
+//  ValueOrDie() - Returns the underlying value. If the state is not valid this
+//          call will crash on a CHECK.
+//  ValueOrDefault() - Returns the current value, or the supplied default if the
+//          state is not valid (will not trigger a CHECK).
+//
+// The following wrapper functions can be used to avoid the template
+// disambiguator syntax when converting a destination type.
+//   IsValidForType<>() in place of: a.template IsValid<Dst>()
+//   ValueOrDieForType<>() in place of: a.template ValueOrDie()
+//   ValueOrDefaultForType<>() in place of: a.template ValueOrDefault(default)
+//
+// The following are general utility methods that are useful for converting
+// between arithmetic types and CheckedNumeric types:
+//  CheckedNumeric::Cast<Dst>() - Instance method returning a CheckedNumeric
+//          derived from casting the current instance to a CheckedNumeric of
+//          the supplied destination type.
+//  MakeCheckedNum() - Creates a new CheckedNumeric from the underlying type of
+//          the supplied arithmetic, CheckedNumeric, or StrictNumeric type.
+//
+// Comparison operations are explicitly not supported because they could result
+// in a crash on an unexpected CHECK condition. You should use patterns like the
+// following for comparisons:
+//   CheckedNumeric<size_t> checked_size = untrusted_input_value;
+//   checked_size += HEADER LENGTH;
+//   if (checked_size.IsValid() && checked_size.ValueOrDie() < buffer_size)
+//     Do stuff...
+
+template <typename T>
+class CheckedNumeric {
+  static_assert(std::is_arithmetic<T>::value,
+                "CheckedNumeric<T>: T must be a numeric type.");
+
+ public:
+  using type = T;
+
+  constexpr CheckedNumeric() {}
+
+  // Copy constructor.
+  template <typename Src>
+  constexpr CheckedNumeric(const CheckedNumeric<Src>& rhs)
+      : state_(rhs.state_.value(), rhs.IsValid()) {}
+
+  template <typename Src>
+  friend class CheckedNumeric;
+
+  // This is not an explicit constructor because we implicitly upgrade regular
+  // numerics to CheckedNumerics to make them easier to use.
+  template <typename Src>
+  constexpr CheckedNumeric(Src value)  // NOLINT(runtime/explicit)
+      : state_(value) {
+    static_assert(std::is_arithmetic<Src>::value, "Argument must be numeric.");
+  }
+
+  // This is not an explicit constructor because we want a seamless conversion
+  // from StrictNumeric types.
+  template <typename Src>
+  constexpr CheckedNumeric(
+      StrictNumeric<Src> value)  // NOLINT(runtime/explicit)
+      : state_(static_cast<Src>(value)) {}
+
+  // IsValid() - The public API to test if a CheckedNumeric is currently valid.
+  // A range checked destination type can be supplied using the Dst template
+  // parameter.
+  template <typename Dst = T>
+  constexpr bool IsValid() const {
+    return state_.is_valid() &&
+           IsValueInRangeForNumericType<Dst>(state_.value());
+  }
+
+  // AssignIfValid(Dst) - Assigns the underlying value if it is currently valid
+  // and is within the range supported by the destination type. Returns true if
+  // successful and false otherwise.
+  template <typename Dst>
+  constexpr bool AssignIfValid(Dst* result) const {
+    return IsValid<Dst>() ? ((*result = static_cast<Dst>(state_.value())), true)
+                          : false;
+  }
+
+  // ValueOrDie() - The primary accessor for the underlying value. If the
+  // current state is not valid it will CHECK and crash.
+  // A range checked destination type can be supplied using the Dst template
+  // parameter, which will trigger a CHECK if the value is not in bounds for
+  // the destination.
+  // The CHECK behavior can be overridden by supplying a handler as a
+  // template parameter, for test code, etc. However, the handler cannot access
+  // the underlying value, and it is not available through other means.
+  template <typename Dst = T, class CheckHandler = CheckOnFailure>
+  constexpr StrictNumeric<Dst> ValueOrDie() const {
+    return IsValid<Dst>() ? static_cast<Dst>(state_.value())
+                          : CheckHandler::template HandleFailure<Dst>();
+  }
+
+  // ValueOrDefault(T default_value) - A convenience method that returns the
+  // current value if the state is valid, and the supplied default_value for
+  // any other state.
+  // A range checked destination type can be supplied using the Dst template
+  // parameter. WARNING: This function may fail to compile or CHECK at runtime
+  // if the supplied default_value is not within range of the destination type.
+  template <typename Dst = T, typename Src>
+  constexpr StrictNumeric<Dst> ValueOrDefault(const Src default_value) const {
+    return IsValid<Dst>() ? static_cast<Dst>(state_.value())
+                          : checked_cast<Dst>(default_value);
+  }
+
+  // Returns a checked numeric of the specified type, cast from the current
+  // CheckedNumeric. If the current state is invalid or the destination cannot
+  // represent the result then the returned CheckedNumeric will be invalid.
+  template <typename Dst>
+  constexpr CheckedNumeric<typename UnderlyingType<Dst>::type> Cast() const {
+    return *this;
+  }
+
+  // This friend method is available solely for providing more detailed logging
+  // in the the tests. Do not implement it in production code, because the
+  // underlying values may change at any time.
+  template <typename U>
+  friend U GetNumericValueForTest(const CheckedNumeric<U>& src);
+
+  // Prototypes for the supported arithmetic operator overloads.
+  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);
+  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);
+  template <typename Src>
+  CheckedNumeric& operator|=(const Src rhs);
+  template <typename Src>
+  CheckedNumeric& operator^=(const Src rhs);
+
+  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()));
+  }
+
+  constexpr CheckedNumeric operator~() const {
+    return CheckedNumeric<decltype(InvertWrapper(T()))>(
+        InvertWrapper(state_.value()), IsValid());
+  }
+
+  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>(
+        static_cast<result_type>(
+            IsGreater<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
+                ? state_.value()
+                : Wrapper<U>::value(rhs)),
+        state_.is_valid() && Wrapper<U>::is_valid(rhs));
+  }
+
+  template <typename U>
+  constexpr CheckedNumeric<typename MathWrapper<CheckedMinOp, T, U>::type> Min(
+      const U rhs) const {
+    using R = typename UnderlyingType<U>::type;
+    using result_type = typename MathWrapper<CheckedMinOp, 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>(
+        static_cast<result_type>(
+            IsLess<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
+                ? state_.value()
+                : Wrapper<U>::value(rhs)),
+        state_.is_valid() && Wrapper<U>::is_valid(rhs));
+  }
+
+  // This function is available only for integral types. It returns an unsigned
+  // integer of the same width as the source type, containing the absolute value
+  // of the source, and properly handling signed min.
+  constexpr CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>
+  UnsignedAbs() const {
+    return CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>(
+        SafeUnsignedAbs(state_.value()), state_.is_valid());
+  }
+
+  CheckedNumeric& operator++() {
+    *this += 1;
+    return *this;
+  }
+
+  CheckedNumeric operator++(int) {
+    CheckedNumeric value = *this;
+    *this += 1;
+    return value;
+  }
+
+  CheckedNumeric& operator--() {
+    *this -= 1;
+    return *this;
+  }
+
+  CheckedNumeric operator--(int) {
+    CheckedNumeric value = *this;
+    *this -= 1;
+    return value;
+  }
+
+  // These perform the actual math operations on the CheckedNumerics.
+  // Binary arithmetic operations.
+  template <template <typename, typename, typename> class M,
+            typename L,
+            typename R>
+  static CheckedNumeric MathOp(const L lhs, const R rhs) {
+    using Math = typename MathWrapper<M, L, R>::math;
+    T result = 0;
+    bool is_valid =
+        Wrapper<L>::is_valid(lhs) && Wrapper<R>::is_valid(rhs) &&
+        Math::Do(Wrapper<L>::value(lhs), Wrapper<R>::value(rhs), &result);
+    return CheckedNumeric<T>(result, is_valid);
+  }
+
+  // Assignment arithmetic operations.
+  template <template <typename, typename, typename> class M, typename R>
+  CheckedNumeric& MathOp(const R rhs) {
+    using Math = typename MathWrapper<M, T, R>::math;
+    T result = 0;  // Using T as the destination saves a range check.
+    bool is_valid = state_.is_valid() && Wrapper<R>::is_valid(rhs) &&
+                    Math::Do(state_.value(), Wrapper<R>::value(rhs), &result);
+    *this = CheckedNumeric<T>(result, is_valid);
+    return *this;
+  }
+
+ private:
+  CheckedNumericState<T> state_;
+
+  template <typename Src>
+  constexpr CheckedNumeric(Src value, bool is_valid)
+      : state_(value, is_valid) {}
+
+  // These wrappers allow us to handle state the same way for both
+  // CheckedNumeric and POD arithmetic types.
+  template <typename Src>
+  struct Wrapper {
+    static constexpr bool is_valid(Src) { return true; }
+    static constexpr Src value(Src value) { return value; }
+  };
+
+  template <typename Src>
+  struct Wrapper<CheckedNumeric<Src>> {
+    static constexpr bool is_valid(const CheckedNumeric<Src> v) {
+      return v.IsValid();
+    }
+    static constexpr Src value(const CheckedNumeric<Src> v) {
+      return v.state_.value();
+    }
+  };
+
+  template <typename Src>
+  struct Wrapper<StrictNumeric<Src>> {
+    static constexpr bool is_valid(const StrictNumeric<Src>) { return true; }
+    static constexpr Src value(const StrictNumeric<Src> v) {
+      return static_cast<Src>(v);
+    }
+  };
+};
+
+// Convenience functions to avoid the ugly template disambiguator syntax.
+template <typename Dst, typename Src>
+constexpr bool IsValidForType(const CheckedNumeric<Src> value) {
+  return value.template IsValid<Dst>();
+}
+
+template <typename Dst, typename Src>
+constexpr StrictNumeric<Dst> ValueOrDieForType(
+    const CheckedNumeric<Src> value) {
+  return value.template ValueOrDie<Dst>();
+}
+
+template <typename Dst, typename Src, typename Default>
+constexpr StrictNumeric<Dst> ValueOrDefaultForType(
+    const CheckedNumeric<Src> value,
+    const Default default_value) {
+  return value.template ValueOrDefault<Dst>(default_value);
+}
+
+// Convience wrapper to return a new CheckedNumeric from the provided arithmetic
+// or CheckedNumericType.
+template <typename T>
+constexpr CheckedNumeric<typename UnderlyingType<T>::type> MakeCheckedNum(
+    const T value) {
+  return value;
+}
+
+// These implement the variadic wrapper for the math operations.
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R>
+CheckedNumeric<typename MathWrapper<M, L, R>::type> ChkMathOp(const L lhs,
+                                                              const R rhs) {
+  using Math = typename MathWrapper<M, L, R>::math;
+  return CheckedNumeric<typename Math::result_type>::template MathOp<M>(lhs,
+                                                                        rhs);
+}
+
+// General purpose wrapper template for arithmetic operations.
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R,
+          typename... Args>
+CheckedNumeric<typename ResultType<M, L, R, Args...>::type>
+ChkMathOp(const L lhs, const R rhs, const Args... args) {
+  auto tmp = ChkMathOp<M>(lhs, rhs);
+  return tmp.IsValid() ? ChkMathOp<M>(tmp, args...)
+                       : decltype(ChkMathOp<M>(tmp, args...))(tmp);
+}
+
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Add, +, +=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Sub, -, -=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Mul, *, *=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Div, /, /=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Mod, %, %=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Lsh, <<, <<=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Rsh, >>, >>=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, And, &, &=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Or, |, |=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Xor, ^, ^=)
+BASE_NUMERIC_ARITHMETIC_VARIADIC(Checked, Check, Max)
+BASE_NUMERIC_ARITHMETIC_VARIADIC(Checked, Check, Min)
+
+// These are some extra StrictNumeric operators to support simple pointer
+// arithmetic with our result types. Since wrapping on a pointer is always
+// bad, we trigger the CHECK condition here.
+template <typename L, typename R>
+L* operator+(L* lhs, const StrictNumeric<R> rhs) {
+  uintptr_t result = CheckAdd(reinterpret_cast<uintptr_t>(lhs),
+                              CheckMul(sizeof(L), static_cast<R>(rhs)))
+                         .template ValueOrDie<uintptr_t>();
+  return reinterpret_cast<L*>(result);
+}
+
+template <typename L, typename R>
+L* operator-(L* lhs, const StrictNumeric<R> rhs) {
+  uintptr_t result = CheckSub(reinterpret_cast<uintptr_t>(lhs),
+                              CheckMul(sizeof(L), static_cast<R>(rhs)))
+                         .template ValueOrDie<uintptr_t>();
+  return reinterpret_cast<L*>(result);
+}
+
+}  // namespace internal
+
+using internal::CheckedNumeric;
+using internal::IsValidForType;
+using internal::ValueOrDieForType;
+using internal::ValueOrDefaultForType;
+using internal::MakeCheckedNum;
+using internal::CheckMax;
+using internal::CheckMin;
+using internal::CheckAdd;
+using internal::CheckSub;
+using internal::CheckMul;
+using internal::CheckDiv;
+using internal::CheckMod;
+using internal::CheckLsh;
+using internal::CheckRsh;
+using internal::CheckAnd;
+using internal::CheckOr;
+using internal::CheckXor;
+
+}  // namespace base
+
+#endif  // BASE_NUMERICS_CHECKED_MATH_H_

base/numerics/safe_math_impl.h → base/numerics/checked_math_impl.h

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// 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.
 
-#ifndef BASE_NUMERICS_SAFE_MATH_IMPL_H_
-#define BASE_NUMERICS_SAFE_MATH_IMPL_H_
+#ifndef BASE_NUMERICS_CHECKED_MATH_IMPL_H_
+#define BASE_NUMERICS_CHECKED_MATH_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
@@ -15,33 +15,11 @@
 #include <type_traits>
 
 #include "base/numerics/safe_conversions.h"
+#include "base/numerics/safe_math_shared_impl.h"
 
 namespace base {
 namespace internal {
 
-// Everything from here up to the floating point operations is portable C++,
-// but it may not be fast. This code could be split based on
-// platform/architecture and replaced with potentially faster implementations.
-
-// This is used for UnsignedAbs, where we need to support floating-point
-// template instantiations even though we don't actually support the operations.
-// However, there is no corresponding implementation of e.g. SafeUnsignedAbs,
-// so the float versions will not compile.
-template <typename Numeric,
-          bool IsInteger = std::is_integral<Numeric>::value,
-          bool IsFloat = std::is_floating_point<Numeric>::value>
-struct UnsignedOrFloatForSize;
-
-template <typename Numeric>
-struct UnsignedOrFloatForSize<Numeric, true, false> {
-  using type = typename std::make_unsigned<Numeric>::type;
-};
-
-template <typename Numeric>
-struct UnsignedOrFloatForSize<Numeric, false, true> {
-  using type = Numeric;
-};
-
 // Probe for builtin math overflow support on Clang and version check on GCC.
 #if defined(__has_builtin)
 #define USE_OVERFLOW_BUILTINS (__has_builtin(__builtin_add_overflow))
@@ -444,19 +422,20 @@ struct CheckedMinOp<
 
 // This is just boilerplate that wraps the standard floating point arithmetic.
 // A macro isn't the nicest solution, but it beats rewriting these repeatedly.
-#define BASE_FLOAT_ARITHMETIC_OPS(NAME, OP)                                    \
-  template <typename T, typename U>                                            \
-  struct Checked##NAME##Op<                                                    \
-      T, U, typename std::enable_if<std::is_floating_point<T>::value ||        \
-                                    std::is_floating_point<U>::value>::type> { \
-    using result_type = typename MaxExponentPromotion<T, U>::type;             \
-    template <typename V>                                                      \
-    static bool Do(T x, U y, V* result) {                                      \
-      using Promotion = typename MaxExponentPromotion<T, U>::type;             \
-      Promotion presult = x OP y;                                              \
-      *result = static_cast<V>(presult);                                       \
-      return IsValueInRangeForNumericType<V>(presult);                         \
-    }                                                                          \
+#define BASE_FLOAT_ARITHMETIC_OPS(NAME, OP)                              \
+  template <typename T, typename U>                                      \
+  struct Checked##NAME##Op<                                              \
+      T, U,                                                              \
+      typename std::enable_if<std::is_floating_point<T>::value ||        \
+                              std::is_floating_point<U>::value>::type> { \
+    using result_type = typename MaxExponentPromotion<T, U>::type;       \
+    template <typename V>                                                \
+    static bool Do(T x, U y, V* result) {                                \
+      using Promotion = typename MaxExponentPromotion<T, U>::type;       \
+      Promotion presult = x OP y;                                        \
+      *result = static_cast<V>(presult);                                 \
+      return IsValueInRangeForNumericType<V>(presult);                   \
+    }                                                                    \
   };
 
 BASE_FLOAT_ARITHMETIC_OPS(Add, +)
@@ -466,45 +445,6 @@ BASE_FLOAT_ARITHMETIC_OPS(Div, /)
 
 #undef BASE_FLOAT_ARITHMETIC_OPS
 
-// Wrap the unary operations to allow SFINAE when instantiating integrals versus
-// floating points. These don't perform any overflow checking. Rather, they
-// exhibit well-defined overflow semantics and rely on the caller to detect
-// if an overflow occured.
-
-template <typename T,
-          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
-constexpr T NegateWrapper(T value) {
-  using UnsignedT = typename std::make_unsigned<T>::type;
-  // This will compile to a NEG on Intel, and is normal negation on ARM.
-  return static_cast<T>(UnsignedT(0) - static_cast<UnsignedT>(value));
-}
-
-template <
-    typename T,
-    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
-constexpr T NegateWrapper(T value) {
-  return -value;
-}
-
-template <typename T,
-          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
-constexpr typename std::make_unsigned<T>::type InvertWrapper(T value) {
-  return ~value;
-}
-
-template <typename T,
-          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
-constexpr T AbsWrapper(T value) {
-  return static_cast<T>(SafeUnsignedAbs(value));
-}
-
-template <
-    typename T,
-    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
-constexpr T AbsWrapper(T value) {
-  return value < 0 ? -value : value;
-}
-
 // Floats carry around their validity state with them, but integers do not. So,
 // we wrap the underlying value in a specialization in order to hide that detail
 // and expose an interface via accessors.
@@ -523,8 +463,8 @@ struct GetNumericRepresentation {
                                                         : NUMERIC_UNKNOWN);
 };
 
-template <typename T, NumericRepresentation type =
-                          GetNumericRepresentation<T>::value>
+template <typename T,
+          NumericRepresentation type = GetNumericRepresentation<T>::value>
 class CheckedNumericState {};
 
 // Integrals require quite a bit of additional housekeeping to manage state.
@@ -625,17 +565,7 @@ class CheckedNumericState<T, NUMERIC_FLOATING> {
   constexpr T value() const { return value_; }
 };
 
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R>
-struct MathWrapper {
-  using math = M<typename UnderlyingType<L>::type,
-                 typename UnderlyingType<R>::type,
-                 void>;
-  using type = typename math::result_type;
-};
-
 }  // namespace internal
 }  // namespace base
 
-#endif  // BASE_NUMERICS_SAFE_MATH_IMPL_H_
+#endif  // BASE_NUMERICS_CHECKED_MATH_IMPL_H_

base/numerics/safe_conversions_impl.h

@@ -537,6 +537,9 @@ struct ArithmeticOrUnderlyingEnum<T, false> {
 template <typename T>
 class CheckedNumeric;
 
+template <typename T>
+class ClampedNumeric;
+
 template <typename T>
 class StrictNumeric;
 
@@ -554,6 +557,16 @@ 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;
 };
 
@@ -562,6 +575,7 @@ 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;
 };
 
@@ -572,6 +586,13 @@ struct IsCheckedOp {
       (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);
+};
+
 template <typename L, typename R>
 struct IsStrictOp {
   static const bool value =
@@ -702,7 +723,7 @@ constexpr bool SafeCompare(const L lhs, const R rhs) {
                    static_cast<BigType>(static_cast<R>(rhs)))
              // Let the template functions figure it out for mixed types.
              : C<L, R>::Test(lhs, rhs);
-};
+}
 
 }  // namespace internal
 }  // namespace base

base/numerics/safe_math.h

@@ -5,504 +5,7 @@
 #ifndef BASE_NUMERICS_SAFE_MATH_H_
 #define BASE_NUMERICS_SAFE_MATH_H_
 
-#include <stddef.h>
-
-#include <limits>
-#include <type_traits>
-
-#include "base/numerics/safe_math_impl.h"
-
-namespace base {
-namespace internal {
-
-// CheckedNumeric<> implements all the logic and operators for detecting integer
-// boundary conditions such as overflow, underflow, and invalid conversions.
-// The CheckedNumeric type implicitly converts from floating point and integer
-// data types, and contains overloads for basic arithmetic operations (i.e.: +,
-// -, *, / for all types and %, <<, >>, &, |, ^ for integers). Type promotions
-// are a slightly modified version of the standard C arithmetic rules with the
-// two differences being that there is no default promotion to int and bitwise
-// logical operations always return an unsigned of the wider type.
-//
-// You may also use one of the variadic convenience functions, which accept
-// standard arithmetic or CheckedNumeric types, perform arithmetic operations,
-// and return a CheckedNumeric result. The supported functions are:
-//  CheckAdd() - Addition.
-//  CheckSub() - Subtraction.
-//  CheckMul() - Multiplication.
-//  CheckDiv() - Division.
-//  CheckMod() - Modulous (integer only).
-//  CheckLsh() - Left integer shift (integer only).
-//  CheckRsh() - Right integer shift (integer only).
-//  CheckAnd() - Bitwise AND (integer only with unsigned result).
-//  CheckOr()  - Bitwise OR (integer only with unsigned result).
-//  CheckXor() - Bitwise XOR (integer only with unsigned result).
-//  CheckMax() - Maximum of supplied arguments.
-//  CheckMin() - Minimum of supplied arguments.
-//
-// The unary negation, increment, and decrement operators are supported, along
-// with the following unary arithmetic methods, which return a new
-// CheckedNumeric as a result of the operation:
-//  Abs() - Absolute value.
-//  UnsignedAbs() - Absolute value as an equal-width unsigned underlying type
-//          (valid for only integral types).
-//  Max() - Returns whichever is greater of the current instance or argument.
-//          The underlying return type is whichever has the greatest magnitude.
-//  Min() - Returns whichever is lowest of the current instance or argument.
-//          The underlying return type is whichever has can represent the lowest
-//          number in the smallest width (e.g. int8_t over unsigned, int over
-//          int8_t, and float over int).
-//
-// The following methods convert from CheckedNumeric to standard numeric values:
-//  AssignIfValid() - Assigns the underlying value to the supplied destination
-//          pointer if the value is currently valid and within the range
-//          supported by the destination type. Returns true on success.
-//  ****************************************************************************
-//  *  WARNING: All of the following functions return a StrictNumeric, which   *
-//  *  is valid for comparison and assignment operations, but will trigger a   *
-//  *  compile failure on attempts to assign to a type of insufficient range.  *
-//  ****************************************************************************
-//  IsValid() - Returns true if the underlying numeric value is valid (i.e. has
-//          has not wrapped and is not the result of an invalid conversion).
-//  ValueOrDie() - Returns the underlying value. If the state is not valid this
-//          call will crash on a CHECK.
-//  ValueOrDefault() - Returns the current value, or the supplied default if the
-//          state is not valid (will not trigger a CHECK).
-//
-// The following wrapper functions can be used to avoid the template
-// disambiguator syntax when converting a destination type.
-//   IsValidForType<>() in place of: a.template IsValid<Dst>()
-//   ValueOrDieForType<>() in place of: a.template ValueOrDie()
-//   ValueOrDefaultForType<>() in place of: a.template ValueOrDefault(default)
-//
-// The following are general utility methods that are useful for converting
-// between arithmetic types and CheckedNumeric types:
-//  CheckedNumeric::Cast<Dst>() - Instance method returning a CheckedNumeric
-//          derived from casting the current instance to a CheckedNumeric of
-//          the supplied destination type.
-//  MakeCheckedNum() - Creates a new CheckedNumeric from the underlying type of
-//          the supplied arithmetic, CheckedNumeric, or StrictNumeric type.
-//
-// Comparison operations are explicitly not supported because they could result
-// in a crash on an unexpected CHECK condition. You should use patterns like the
-// following for comparisons:
-//   CheckedNumeric<size_t> checked_size = untrusted_input_value;
-//   checked_size += HEADER LENGTH;
-//   if (checked_size.IsValid() && checked_size.ValueOrDie() < buffer_size)
-//     Do stuff...
-
-template <typename T>
-class CheckedNumeric {
-  static_assert(std::is_arithmetic<T>::value,
-                "CheckedNumeric<T>: T must be a numeric type.");
-
- public:
-  using type = T;
-
-  constexpr CheckedNumeric() {}
-
-  // Copy constructor.
-  template <typename Src>
-  constexpr CheckedNumeric(const CheckedNumeric<Src>& rhs)
-      : state_(rhs.state_.value(), rhs.IsValid()) {}
-
-  template <typename Src>
-  friend class CheckedNumeric;
-
-  // This is not an explicit constructor because we implicitly upgrade regular
-  // numerics to CheckedNumerics to make them easier to use.
-  template <typename Src>
-  constexpr CheckedNumeric(Src value)  // NOLINT(runtime/explicit)
-      : state_(value) {
-    static_assert(std::is_arithmetic<Src>::value, "Argument must be numeric.");
-  }
-
-  // This is not an explicit constructor because we want a seamless conversion
-  // from StrictNumeric types.
-  template <typename Src>
-  constexpr CheckedNumeric(
-      StrictNumeric<Src> value)  // NOLINT(runtime/explicit)
-      : state_(static_cast<Src>(value)) {}
-
-  // IsValid() - The public API to test if a CheckedNumeric is currently valid.
-  // A range checked destination type can be supplied using the Dst template
-  // parameter.
-  template <typename Dst = T>
-  constexpr bool IsValid() const {
-    return state_.is_valid() &&
-           IsValueInRangeForNumericType<Dst>(state_.value());
-  }
-
-  // AssignIfValid(Dst) - Assigns the underlying value if it is currently valid
-  // and is within the range supported by the destination type. Returns true if
-  // successful and false otherwise.
-  template <typename Dst>
-  constexpr bool AssignIfValid(Dst* result) const {
-    return IsValid<Dst>() ? ((*result = static_cast<Dst>(state_.value())), true)
-                          : false;
-  }
-
-  // ValueOrDie() - The primary accessor for the underlying value. If the
-  // current state is not valid it will CHECK and crash.
-  // A range checked destination type can be supplied using the Dst template
-  // parameter, which will trigger a CHECK if the value is not in bounds for
-  // the destination.
-  // The CHECK behavior can be overridden by supplying a handler as a
-  // template parameter, for test code, etc. However, the handler cannot access
-  // the underlying value, and it is not available through other means.
-  template <typename Dst = T, class CheckHandler = CheckOnFailure>
-  constexpr StrictNumeric<Dst> ValueOrDie() const {
-    return IsValid<Dst>() ? static_cast<Dst>(state_.value())
-                          : CheckHandler::template HandleFailure<Dst>();
-  }
-
-  // ValueOrDefault(T default_value) - A convenience method that returns the
-  // current value if the state is valid, and the supplied default_value for
-  // any other state.
-  // A range checked destination type can be supplied using the Dst template
-  // parameter. WARNING: This function may fail to compile or CHECK at runtime
-  // if the supplied default_value is not within range of the destination type.
-  template <typename Dst = T, typename Src>
-  constexpr StrictNumeric<Dst> ValueOrDefault(const Src default_value) const {
-    return IsValid<Dst>() ? static_cast<Dst>(state_.value())
-                          : checked_cast<Dst>(default_value);
-  }
-
-  // Returns a checked numeric of the specified type, cast from the current
-  // CheckedNumeric. If the current state is invalid or the destination cannot
-  // represent the result then the returned CheckedNumeric will be invalid.
-  template <typename Dst>
-  constexpr CheckedNumeric<typename UnderlyingType<Dst>::type> Cast() const {
-    return *this;
-  }
-
-  // This friend method is available solely for providing more detailed logging
-  // in the the tests. Do not implement it in production code, because the
-  // underlying values may change at any time.
-  template <typename U>
-  friend U GetNumericValueForTest(const CheckedNumeric<U>& src);
-
-  // Prototypes for the supported arithmetic operator overloads.
-  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);
-  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);
-  template <typename Src>
-  CheckedNumeric& operator|=(const Src rhs);
-  template <typename Src>
-  CheckedNumeric& operator^=(const Src rhs);
-
-  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()));
-  }
-
-  constexpr CheckedNumeric operator~() const {
-    return CheckedNumeric<decltype(InvertWrapper(T()))>(
-        InvertWrapper(state_.value()), IsValid());
-  }
-
-  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>(
-        static_cast<result_type>(
-            IsGreater<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
-                ? state_.value()
-                : Wrapper<U>::value(rhs)),
-        state_.is_valid() && Wrapper<U>::is_valid(rhs));
-  }
-
-  template <typename U>
-  constexpr CheckedNumeric<typename MathWrapper<CheckedMinOp, T, U>::type> Min(
-      const U rhs) const {
-    using R = typename UnderlyingType<U>::type;
-    using result_type = typename MathWrapper<CheckedMinOp, 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>(
-        static_cast<result_type>(
-            IsLess<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
-                ? state_.value()
-                : Wrapper<U>::value(rhs)),
-        state_.is_valid() && Wrapper<U>::is_valid(rhs));
-  }
-
-  // This function is available only for integral types. It returns an unsigned
-  // integer of the same width as the source type, containing the absolute value
-  // of the source, and properly handling signed min.
-  constexpr CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>
-  UnsignedAbs() const {
-    return CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>(
-        SafeUnsignedAbs(state_.value()), state_.is_valid());
-  }
-
-  CheckedNumeric& operator++() {
-    *this += 1;
-    return *this;
-  }
-
-  CheckedNumeric operator++(int) {
-    CheckedNumeric value = *this;
-    *this += 1;
-    return value;
-  }
-
-  CheckedNumeric& operator--() {
-    *this -= 1;
-    return *this;
-  }
-
-  CheckedNumeric operator--(int) {
-    CheckedNumeric value = *this;
-    *this -= 1;
-    return value;
-  }
-
-  // These perform the actual math operations on the CheckedNumerics.
-  // Binary arithmetic operations.
-  template <template <typename, typename, typename> class M,
-            typename L,
-            typename R>
-  static CheckedNumeric MathOp(const L lhs, const R rhs) {
-    using Math = typename MathWrapper<M, L, R>::math;
-    T result = 0;
-    bool is_valid =
-        Wrapper<L>::is_valid(lhs) && Wrapper<R>::is_valid(rhs) &&
-        Math::Do(Wrapper<L>::value(lhs), Wrapper<R>::value(rhs), &result);
-    return CheckedNumeric<T>(result, is_valid);
-  };
-
-  // Assignment arithmetic operations.
-  template <template <typename, typename, typename> class M, typename R>
-  CheckedNumeric& MathOp(const R rhs) {
-    using Math = typename MathWrapper<M, T, R>::math;
-    T result = 0;  // Using T as the destination saves a range check.
-    bool is_valid = state_.is_valid() && Wrapper<R>::is_valid(rhs) &&
-                    Math::Do(state_.value(), Wrapper<R>::value(rhs), &result);
-    *this = CheckedNumeric<T>(result, is_valid);
-    return *this;
-  };
-
- private:
-  CheckedNumericState<T> state_;
-
-  template <typename Src>
-  constexpr CheckedNumeric(Src value, bool is_valid)
-      : state_(value, is_valid) {}
-
-  // These wrappers allow us to handle state the same way for both
-  // CheckedNumeric and POD arithmetic types.
-  template <typename Src>
-  struct Wrapper {
-    static constexpr bool is_valid(Src) { return true; }
-    static constexpr Src value(Src value) { return value; }
-  };
-
-  template <typename Src>
-  struct Wrapper<CheckedNumeric<Src>> {
-    static constexpr bool is_valid(const CheckedNumeric<Src> v) {
-      return v.IsValid();
-    }
-    static constexpr Src value(const CheckedNumeric<Src> v) {
-      return v.state_.value();
-    }
-  };
-
-  template <typename Src>
-  struct Wrapper<StrictNumeric<Src>> {
-    static constexpr bool is_valid(const StrictNumeric<Src>) { return true; }
-    static constexpr Src value(const StrictNumeric<Src> v) {
-      return static_cast<Src>(v);
-    }
-  };
-};
-
-// Convenience functions to avoid the ugly template disambiguator syntax.
-template <typename Dst, typename Src>
-constexpr bool IsValidForType(const CheckedNumeric<Src> value) {
-  return value.template IsValid<Dst>();
-}
-
-template <typename Dst, typename Src>
-constexpr StrictNumeric<Dst> ValueOrDieForType(
-    const CheckedNumeric<Src> value) {
-  return value.template ValueOrDie<Dst>();
-}
-
-template <typename Dst, typename Src, typename Default>
-constexpr StrictNumeric<Dst> ValueOrDefaultForType(
-    const CheckedNumeric<Src> value,
-    const Default default_value) {
-  return value.template ValueOrDefault<Dst>(default_value);
-}
-
-// These variadic templates work out the return types.
-// TODO(jschuh): Rip all this out once we have C++14 non-trailing auto support.
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R,
-          typename... Args>
-struct ResultType;
-
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R>
-struct ResultType<M, L, R> {
-  using type = typename MathWrapper<M, L, R>::type;
-};
-
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R,
-          typename... Args>
-struct ResultType {
-  using type =
-      typename ResultType<M, typename ResultType<M, L, R>::type, Args...>::type;
-};
-
-// Convience wrapper to return a new CheckedNumeric from the provided arithmetic
-// or CheckedNumericType.
-template <typename T>
-constexpr CheckedNumeric<typename UnderlyingType<T>::type> MakeCheckedNum(
-    const T value) {
-  return value;
-}
-
-// These implement the variadic wrapper for the math operations.
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R>
-CheckedNumeric<typename MathWrapper<M, L, R>::type> ChkMathOp(const L lhs,
-                                                              const R rhs) {
-  using Math = typename MathWrapper<M, L, R>::math;
-  return CheckedNumeric<typename Math::result_type>::template MathOp<M>(lhs,
-                                                                        rhs);
-}
-
-// General purpose wrapper template for arithmetic operations.
-template <template <typename, typename, typename> class M,
-          typename L,
-          typename R,
-          typename... Args>
-CheckedNumeric<typename ResultType<M, L, R, Args...>::type>
-ChkMathOp(const L lhs, const R rhs, const Args... args) {
-  auto tmp = ChkMathOp<M>(lhs, rhs);
-  return tmp.IsValid() ? ChkMathOp<M>(tmp, args...)
-                       : decltype(ChkMathOp<M>(tmp, args...))(tmp);
-};
-
-// The following macros are just boilerplate for the standard arithmetic
-// operator overloads and variadic function templates. A macro isn't the nicest
-// solution, but it beats rewriting these over and over again.
-#define BASE_NUMERIC_ARITHMETIC_VARIADIC(NAME)                                \
-  template <typename L, typename R, typename... Args>                         \
-  CheckedNumeric<typename ResultType<Checked##NAME##Op, L, R, Args...>::type> \
-      Check##NAME(const L lhs, const R rhs, const Args... args) {             \
-    return ChkMathOp<Checked##NAME##Op, L, R, Args...>(lhs, rhs, args...);    \
-  }
-
-#define BASE_NUMERIC_ARITHMETIC_OPERATORS(NAME, OP, COMPOUND_OP)               \
-  /* Binary arithmetic operator for all CheckedNumeric operations. */          \
-  template <typename L, typename R,                                            \
-            typename std::enable_if<IsCheckedOp<L, R>::value>::type* =         \
-                nullptr>                                                       \
-  CheckedNumeric<typename MathWrapper<Checked##NAME##Op, L, R>::type>          \
-  operator OP(const L lhs, const R rhs) {                                      \
-    return decltype(lhs OP rhs)::template MathOp<Checked##NAME##Op>(lhs, rhs); \
-  }                                                                            \
-  /* Assignment arithmetic operator implementation from CheckedNumeric. */     \
-  template <typename L>                                                        \
-  template <typename R>                                                        \
-  CheckedNumeric<L>& CheckedNumeric<L>::operator COMPOUND_OP(const R rhs) {    \
-    return MathOp<Checked##NAME##Op>(rhs);                                     \
-  }                                                                            \
-  /* Variadic arithmetic functions that return CheckedNumeric. */              \
-  BASE_NUMERIC_ARITHMETIC_VARIADIC(NAME)
-
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Add, +, +=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Sub, -, -=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Mul, *, *=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Div, /, /=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Mod, %, %=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Lsh, <<, <<=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Rsh, >>, >>=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(And, &, &=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Or, |, |=)
-BASE_NUMERIC_ARITHMETIC_OPERATORS(Xor, ^, ^=)
-BASE_NUMERIC_ARITHMETIC_VARIADIC(Max)
-BASE_NUMERIC_ARITHMETIC_VARIADIC(Min)
-
-#undef BASE_NUMERIC_ARITHMETIC_VARIADIC
-#undef BASE_NUMERIC_ARITHMETIC_OPERATORS
-
-// These are some extra StrictNumeric operators to support simple pointer
-// arithmetic with our result types. Since wrapping on a pointer is always
-// bad, we trigger the CHECK condition here.
-template <typename L, typename R>
-L* operator+(L* lhs, const StrictNumeric<R> rhs) {
-  uintptr_t result = CheckAdd(reinterpret_cast<uintptr_t>(lhs),
-                              CheckMul(sizeof(L), static_cast<R>(rhs)))
-                         .template ValueOrDie<uintptr_t>();
-  return reinterpret_cast<L*>(result);
-}
-
-template <typename L, typename R>
-L* operator-(L* lhs, const StrictNumeric<R> rhs) {
-  uintptr_t result = CheckSub(reinterpret_cast<uintptr_t>(lhs),
-                              CheckMul(sizeof(L), static_cast<R>(rhs)))
-                         .template ValueOrDie<uintptr_t>();
-  return reinterpret_cast<L*>(result);
-}
-
-}  // namespace internal
-
-using internal::CheckedNumeric;
-using internal::IsValidForType;
-using internal::ValueOrDieForType;
-using internal::ValueOrDefaultForType;
-using internal::MakeCheckedNum;
-using internal::CheckMax;
-using internal::CheckMin;
-using internal::CheckAdd;
-using internal::CheckSub;
-using internal::CheckMul;
-using internal::CheckDiv;
-using internal::CheckMod;
-using internal::CheckLsh;
-using internal::CheckRsh;
-using internal::CheckAnd;
-using internal::CheckOr;
-using internal::CheckXor;
-
-}  // namespace base
+#include "base/numerics/checked_math.h"
+#include "base/numerics/safe_conversions.h"
 
 #endif  // BASE_NUMERICS_SAFE_MATH_H_

base/numerics/safe_math_shared_impl.h

+// 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.
+
+#ifndef BASE_NUMERICS_SAFE_MATH_SHARED_IMPL_H_
+#define BASE_NUMERICS_SAFE_MATH_SHARED_IMPL_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <climits>
+#include <cmath>
+#include <cstdlib>
+#include <limits>
+#include <type_traits>
+
+#include "base/numerics/safe_conversions.h"
+
+namespace base {
+namespace internal {
+
+// This is used for UnsignedAbs, where we need to support floating-point
+// template instantiations even though we don't actually support the operations.
+// However, there is no corresponding implementation of e.g. SafeUnsignedAbs,
+// so the float versions will not compile.
+template <typename Numeric,
+          bool IsInteger = std::is_integral<Numeric>::value,
+          bool IsFloat = std::is_floating_point<Numeric>::value>
+struct UnsignedOrFloatForSize;
+
+template <typename Numeric>
+struct UnsignedOrFloatForSize<Numeric, true, false> {
+  using type = typename std::make_unsigned<Numeric>::type;
+};
+
+template <typename Numeric>
+struct UnsignedOrFloatForSize<Numeric, false, true> {
+  using type = Numeric;
+};
+
+// Wrap the unary operations to allow SFINAE when instantiating integrals versus
+// floating points. These don't perform any overflow checking. Rather, they
+// exhibit well-defined overflow semantics and rely on the caller to detect
+// if an overflow occured.
+
+template <typename T,
+          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
+constexpr T NegateWrapper(T value) {
+  using UnsignedT = typename std::make_unsigned<T>::type;
+  // This will compile to a NEG on Intel, and is normal negation on ARM.
+  return static_cast<T>(UnsignedT(0) - static_cast<UnsignedT>(value));
+}
+
+template <
+    typename T,
+    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
+constexpr T NegateWrapper(T value) {
+  return -value;
+}
+
+template <typename T,
+          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
+constexpr typename std::make_unsigned<T>::type InvertWrapper(T value) {
+  return ~value;
+}
+
+template <typename T,
+          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
+constexpr T AbsWrapper(T value) {
+  return static_cast<T>(SafeUnsignedAbs(value));
+}
+
+template <
+    typename T,
+    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
+constexpr T AbsWrapper(T value) {
+  return value < 0 ? -value : value;
+}
+
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R>
+struct MathWrapper {
+  using math = M<typename UnderlyingType<L>::type,
+                 typename UnderlyingType<R>::type,
+                 void>;
+  using type = typename math::result_type;
+};
+
+// These variadic templates work out the return types.
+// TODO(jschuh): Rip all this out once we have C++14 non-trailing auto support.
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R,
+          typename... Args>
+struct ResultType;
+
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R>
+struct ResultType<M, L, R> {
+  using type = typename MathWrapper<M, L, R>::type;
+};
+
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R,
+          typename... Args>
+struct ResultType {
+  using type =
+      typename ResultType<M, typename ResultType<M, L, R>::type, Args...>::type;
+};
+
+// The following macros are just boilerplate for the standard arithmetic
+// operator overloads and variadic function templates. A macro isn't the nicest
+// solution, but it beats rewriting these over and over again.
+#define BASE_NUMERIC_ARITHMETIC_VARIADIC(CLASS, CL_ABBR, OP_NAME)              \
+  template <typename L, typename R, typename... Args>                          \
+  CLASS##Numeric<typename ResultType<CLASS##OP_NAME##Op, L, R, Args...>::type> \
+      CL_ABBR##OP_NAME(const L lhs, const R rhs, const Args... args) {         \
+    return ChkMathOp<CLASS##OP_NAME##Op, L, R, Args...>(lhs, rhs, args...);    \
+  }
+
+#define BASE_NUMERIC_ARITHMETIC_OPERATORS(CLASS, CL_ABBR, OP_NAME, OP, CMP_OP) \
+  /* Binary arithmetic operator for all CheckedNumeric operations. */          \
+  template <typename L, typename R,                                            \
+            typename std::enable_if<IsCheckedOp<L, R>::value>::type* =         \
+                nullptr>                                                       \
+  CheckedNumeric<typename MathWrapper<CLASS##OP_NAME##Op, L, R>::type>         \
+  operator OP(const L lhs, const R rhs) {                                      \
+    return decltype(lhs OP rhs)::template MathOp<CLASS##OP_NAME##Op>(lhs,      \
+                                                                     rhs);     \
+  }                                                                            \
+  /* Assignment arithmetic operator implementation from CheckedNumeric. */     \
+  template <typename L>                                                        \
+  template <typename R>                                                        \
+  CheckedNumeric<L>& CheckedNumeric<L>::operator CMP_OP(const R rhs) {         \
+    return MathOp<CLASS##OP_NAME##Op>(rhs);                                    \
+  }                                                                            \
+  /* Variadic arithmetic functions that return CheckedNumeric. */              \
+  BASE_NUMERIC_ARITHMETIC_VARIADIC(CLASS, CL_ABBR, OP_NAME)
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_NUMERICS_SAFE_MATH_SHARED_IMPL_H_