Update safe numerics package to get bitwise ops

Fix callers conventions to avoid ambiguity.
Fix bad bounds check unmasked by change.
Directly include headers no longer pulled in by numerics itself.

Review-Url: https://codereview.chromium.org/2640143003

1 files changed, 605 insertions, 89 deletions

diff --git a/third_party/base/numerics/safe_conversions_impl.h b/third_party/base/numerics/safe_conversions_impl.h
index e1c4c3b756..2a7ce146e3 100644
--- a/third_party/base/numerics/safe_conversions_impl.h
+++ b/third_party/base/numerics/safe_conversions_impl.h
@@ -2,29 +2,81 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
-#define PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
+#ifndef PDFIUM_THIRD_PARTY_BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
+#define PDFIUM_THIRD_PARTY_BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
 
-#include <assert.h>
-#include <limits>
+#include <stdint.h>
 
-#include "third_party/base/macros.h"
+#include <limits>
+#include <type_traits>
 
 namespace pdfium {
 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) ? 0 - static_cast<UnsignedT>(value)
+                                : static_cast<UnsignedT>(value);
+}
+
 enum IntegerRepresentation {
   INTEGER_REPRESENTATION_UNSIGNED,
   INTEGER_REPRESENTATION_SIGNED
@@ -32,7 +84,7 @@ 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 {
@@ -43,16 +95,14 @@ 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
@@ -87,132 +137,598 @@ 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) {
-  assert(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.
+// 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>
+// 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 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());
+  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>
+// 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 RangeConstraint Check(Src value) {
-    return GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), true);
+  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>
+// 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 RangeConstraint Check(Src value) {
-    return sizeof(Dst) > sizeof(Src)
-               ? RANGE_VALID
-               : GetRangeConstraint(
-                     value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
-                     true);
+  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>
+// 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 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));
+  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()));
   }
 };
 
-template <typename Dst, typename Src>
-inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
-  COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
-                 argument_must_be_numeric);
-  COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
-                 result_must_be_numeric);
-  return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
+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;
+};
+
+// This hacks around libstdc++ 4.6 missing stuff in type_traits.
+#if defined(__GLIBCXX__)
+#define PRIV_GLIBCXX_4_7_0 20120322
+#define PRIV_GLIBCXX_4_5_4 20120702
+#define PRIV_GLIBCXX_4_6_4 20121127
+#if (__GLIBCXX__ < PRIV_GLIBCXX_4_7_0 || __GLIBCXX__ == PRIV_GLIBCXX_4_5_4 || \
+     __GLIBCXX__ == PRIV_GLIBCXX_4_6_4)
+#define PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX
+#undef PRIV_GLIBCXX_4_7_0
+#undef PRIV_GLIBCXX_4_5_4
+#undef PRIV_GLIBCXX_4_6_4
+#endif
+#endif
+
+// 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> {
+#if defined(PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX)
+  using type = __underlying_type(T);
+#else
+  using type = typename std::underlying_type<T>::type;
+#endif
+  static const bool value = std::is_arithmetic<type>::value;
+};
+
+#if defined(PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX)
+#undef PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX
+#endif
+
+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 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_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_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_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 IsStrictOp {
+  static const bool value =
+      UnderlyingType<L>::is_numeric && UnderlyingType<R>::is_numeric &&
+      (UnderlyingType<L>::is_strict || UnderlyingType<R>::is_strict);
+};
+
+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);
+};
+
 }  // namespace internal
 }  // namespace base
 }  // namespace pdfium
 
-#endif  // PDFIUM_THIRD_PARTY_BASE_SAFE_CONVERSIONS_IMPL_H_
+#endif  // PDFIUM_THIRD_PARTY_BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_