Add ClampedNumeric templates

base/numerics/clamped_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_CLAMPED_MATH_H_
+#define BASE_NUMERICS_CLAMPED_MATH_H_
+
+#include <stddef.h>
+
+#include <limits>
+#include <type_traits>
+
+#include "base/numerics/clamped_math_impl.h"
+
+namespace base {
+namespace internal {
+
+template <typename T>
+class ClampedNumeric {
+  static_assert(std::is_arithmetic<T>::value,
+                "ClampedNumeric<T>: T must be a numeric type.");
+
+ public:
+  using type = T;
+
+  constexpr ClampedNumeric() : value_(0) {}
+
+  // Copy constructor.
+  template <typename Src>
+  constexpr ClampedNumeric(const ClampedNumeric<Src>& rhs)
+      : value_(saturated_cast<T>(rhs.value_)) {}
+
+  template <typename Src>
+  friend class ClampedNumeric;
+
+  // This is not an explicit constructor because we implicitly upgrade regular
+  // numerics to ClampedNumerics to make them easier to use.
+  template <typename Src>
+  constexpr ClampedNumeric(Src value)  // NOLINT(runtime/explicit)
+      : value_(saturated_cast<T>(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 ClampedNumeric(
+      StrictNumeric<Src> value)  // NOLINT(runtime/explicit)
+      : value_(saturated_cast<T>(static_cast<Src>(value))) {}
+
+  // Returns a ClampedNumeric of the specified type, cast from the current
+  // ClampedNumeric, and saturated to the destination type.
+  template <typename Dst>
+  constexpr ClampedNumeric<typename UnderlyingType<Dst>::type> Cast() const {
+    return *this;
+  }
+
+  // Prototypes for the supported arithmetic operator overloads.
+  template <typename Src>
+  ClampedNumeric& operator+=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator-=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator*=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator/=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator%=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator<<=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator>>=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator&=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator|=(const Src rhs);
+  template <typename Src>
+  ClampedNumeric& operator^=(const Src rhs);
+
+  constexpr ClampedNumeric operator-() const {
+    return ClampedNumeric<T>(
+        std::is_signed<T>::value
+            ? ((std::is_floating_point<T>::value ||
+                NegateWrapper(value_) != std::numeric_limits<T>::lowest())

[dcheng, 2017/06/30 07:39:30]

I can't help but feel that NegateWrapper / InvertWrapper / AbsWrapper could use
some comments describing how they work / how callers are expected to check for
underflow/overflow conditions.

[jschuh, 2017/07/01 06:31:59]

There already is a comment at the function definition that I think is
sufficient, and explicitly states that the caller must check for overflow.

[dcheng, 2017/07/03 10:01:43]

Right, the comments I was thinking of were more along the lines of how to check
for overflow (and any interesting asides about twos complement math), etc. The
answer is fairly self-evident if you think about it... but as it involves some
clever code, sprinkling in some comments won't hurt.

+                   ? NegateWrapper(value_)
+                   : std::numeric_limits<T>::max())
+            : T(0));  // Clamped unsigned negation is always zero.
+  }
+
+  constexpr ClampedNumeric operator~() const {
+    return ClampedNumeric<decltype(InvertWrapper(T()))>(InvertWrapper(value_));
+  }
+
+  constexpr ClampedNumeric Abs() const {
+    return ClampedNumeric<T>(
+        (!std::is_signed<T>::value || std::is_floating_point<T>::value ||
+         AbsWrapper(value_) != std::numeric_limits<T>::lowest())
+            ? AbsWrapper(value_)
+            : std::numeric_limits<T>::max());
+  }
+
+  template <typename U>
+  constexpr ClampedNumeric<typename MathWrapper<ClampedMaxOp, T, U>::type> Max(
+      const U rhs) const {
+    using result_type = typename MathWrapper<ClampedMaxOp, T, U>::type;
+    return ClampedNumeric<result_type>(
+        ClampedMaxOp<T, U>(value_, Wrapper<U>::value(rhs)));
+  }
+
+  template <typename U>
+  constexpr ClampedNumeric<typename MathWrapper<ClampedMinOp, T, U>::type> Min(
+      const U rhs) const {
+    using result_type = typename MathWrapper<ClampedMinOp, T, U>::type;
+    return ClampedNumeric<result_type>(
+        ClampedMinOp<T, U>(value_, Wrapper<U>::value(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 ClampedNumeric<typename UnsignedOrFloatForSize<T>::type>
+  UnsignedAbs() const {
+    return ClampedNumeric<typename UnsignedOrFloatForSize<T>::type>(
+        SafeUnsignedAbs(value_));
+  }
+
+  ClampedNumeric& operator++() {
+    *this += 1;
+    return *this;
+  }
+
+  ClampedNumeric operator++(int) {
+    ClampedNumeric value = *this;
+    *this += 1;
+    return value;
+  }
+
+  ClampedNumeric& operator--() {
+    *this -= 1;
+    return *this;
+  }
+
+  ClampedNumeric operator--(int) {
+    ClampedNumeric value = *this;
+    *this -= 1;
+    return value;
+  }
+
+  // These perform the actual math operations on the ClampedNumerics.
+  // Binary arithmetic operations.
+  template <template <typename, typename, typename> class M,
+            typename L,
+            typename R>
+  static ClampedNumeric MathOp(const L lhs, const R rhs) {
+    using Math = typename MathWrapper<M, L, R>::math;
+    return ClampedNumeric<T>(
+        Math::template Do<T>(Wrapper<L>::value(lhs), Wrapper<R>::value(rhs)));
+  }
+
+  // Assignment arithmetic operations.
+  template <template <typename, typename, typename> class M, typename R>
+  ClampedNumeric& MathOp(const R rhs) {
+    using Math = typename MathWrapper<M, T, R>::math;
+    *this =
+        ClampedNumeric<T>(Math::template Do<T>(value_, Wrapper<R>::value(rhs)));
+    return *this;
+  }
+
+  template <typename Dst>
+  constexpr operator Dst() const {
+    return saturated_cast<typename ArithmeticOrUnderlyingEnum<Dst>::type>(
+        value_);
+  }
+
+ private:
+  T value_;
+
+  // These wrappers allow us to handle state the same way for both
+  // ClampedNumeric and POD arithmetic types.
+  template <typename Src>
+  struct Wrapper {
+    static constexpr Src value(Src value) {
+      return static_cast<typename UnderlyingType<Src>::type>(value);
+    }
+  };
+};
+
+// Convience wrapper to return a new ClampedNumeric from the provided arithmetic
+// or ClampedNumericType.
+template <typename T>
+constexpr ClampedNumeric<typename UnderlyingType<T>::type> MakeClampedNum(
+    const T value) {
+  return value;
+}
+
+// Overload the ostream output operator to make logging work nicely.
+template <typename T>
+std::ostream& operator<<(std::ostream& os, const ClampedNumeric<T>& value) {
+  os << static_cast<T>(value);
+  return os;
+}
+
+// These implement the variadic wrapper for the math operations.
+template <template <typename, typename, typename> class M,
+          typename L,
+          typename R>
+ClampedNumeric<typename MathWrapper<M, L, R>::type> ClampMathOp(const L lhs,
+                                                                const R rhs) {
+  using Math = typename MathWrapper<M, L, R>::math;
+  return ClampedNumeric<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>
+ClampedNumeric<typename ResultType<M, L, R, Args...>::type>
+ClampMathOp(const L lhs, const R rhs, const Args... args) {
+  return ClampMathOp<M>(ClampMathOp<M>(lhs, rhs), args...);
+}
+
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Add, +, +=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Sub, -, -=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Mul, *, *=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Div, /, /=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Mod, %, %=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Lsh, <<, <<=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Rsh, >>, >>=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, And, &, &=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Or, |, |=)
+BASE_NUMERIC_ARITHMETIC_OPERATORS(Clamped, Clamp, Xor, ^, ^=)
+BASE_NUMERIC_ARITHMETIC_VARIADIC(Clamped, Clamp, Max)
+BASE_NUMERIC_ARITHMETIC_VARIADIC(Clamped, Clamp, Min)
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsLess, <);
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsLessOrEqual, <=);
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsGreater, >);
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsGreaterOrEqual, >=);
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsEqual, ==);
+BASE_NUMERIC_COMPARISON_OPERATORS(Clamped, IsNotEqual, !=);
+
+}  // namespace internal
+
+using internal::ClampedNumeric;
+using internal::MakeClampedNum;
+using internal::ClampMax;
+using internal::ClampMin;
+using internal::ClampAdd;
+using internal::ClampSub;
+using internal::ClampMul;
+using internal::ClampDiv;
+using internal::ClampMod;
+using internal::ClampLsh;
+using internal::ClampRsh;
+using internal::ClampAnd;
+using internal::ClampOr;
+using internal::ClampXor;
+
+}  // namespace base
+
+#endif  // BASE_NUMERICS_CLAMPED_MATH_H_