chromium/third_party/pdfium/core/fxcrt/numerics/safe_math_shared_impl.h

// Copyright 2024 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CORE_FXCRT_NUMERICS_SAFE_MATH_SHARED_IMPL_H_
#define CORE_FXCRT_NUMERICS_SAFE_MATH_SHARED_IMPL_H_

#include <stddef.h>
#include <stdint.h>

#include <cassert>
#include <climits>
#include <cmath>
#include <cstdlib>
#include <limits>
#include <type_traits>

#include "build/build_config.h"
#include "core/fxcrt/numerics/safe_conversions.h"

#if BUILDFLAG(IS_ASMJS)
// Optimized safe math instructions are incompatible with asmjs.
#define BASE_HAS_OPTIMIZED_SAFE_MATH …
// Where available use builtin math overflow support on Clang and GCC.
#elif !defined(__native_client__) &&                       \
    ((defined(__clang__) &&                                \
      ((__clang_major__ > 3) ||                            \
       (__clang_major__ == 3 && __clang_minor__ >= 4))) || \
     (defined(__GNUC__) && __GNUC__ >= 5))
#include "core/fxcrt/numerics/safe_math_clang_gcc_impl.h"
#define BASE_HAS_OPTIMIZED_SAFE_MATH …
#else
#define BASE_HAS_OPTIMIZED_SAFE_MATH …
#endif

namespace pdfium {
namespace internal {

// These are the non-functioning boilerplate implementations of the optimized
// safe math routines.
#if !BASE_HAS_OPTIMIZED_SAFE_MATH
template <typename T, typename U>
struct CheckedAddFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr bool Do(T, U, V*) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<bool>();
  }
};

template <typename T, typename U>
struct CheckedSubFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr bool Do(T, U, V*) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<bool>();
  }
};

template <typename T, typename U>
struct CheckedMulFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr bool Do(T, U, V*) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<bool>();
  }
};

template <typename T, typename U>
struct ClampedAddFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr V Do(T, U) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<V>();
  }
};

template <typename T, typename U>
struct ClampedSubFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr V Do(T, U) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<V>();
  }
};

template <typename T, typename U>
struct ClampedMulFastOp {
  static const bool is_supported = false;
  template <typename V>
  static constexpr V Do(T, U) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<V>();
  }
};

template <typename T>
struct ClampedNegFastOp {
  static const bool is_supported = false;
  static constexpr T Do(T) {
    // Force a compile failure if instantiated.
    return CheckOnFailure::template HandleFailure<T>();
  }
};
#endif  // BASE_HAS_OPTIMIZED_SAFE_MATH
#undef BASE_HAS_OPTIMIZED_SAFE_MATH

// 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;

UnsignedOrFloatForSize<Numeric, true, false>;

UnsignedOrFloatForSize<Numeric, false, true>;

// 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 occurred.

template <typename T,
          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
constexpr T NegateWrapper(T value) { … }

template <
    typename T,
    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
constexpr T NegateWrapper(T 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) { … }

template <typename T,
          typename std::enable_if<std::is_integral<T>::value>::type* = nullptr>
constexpr T AbsWrapper(T value) { … }

template <
    typename T,
    typename std::enable_if<std::is_floating_point<T>::value>::type* = nullptr>
constexpr T AbsWrapper(T value) { … }

template <template <typename, typename, typename> class M,
          typename L,
          typename R>
struct MathWrapper { … };

// 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) …

#define BASE_NUMERIC_ARITHMETIC_OPERATORS(CLASS, CL_ABBR, OP_NAME, OP, CMP_OP) …

}  // namespace internal
}  // namespace pdfium

#endif  // CORE_FXCRT_NUMERICS_SAFE_MATH_SHARED_IMPL_H_