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- // Copyright 2019 the V8 project authors. All rights reserved.
- // Copyright 2020 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 THIRD_PARTY_FDLIBM_OVERFLOWING_MATH_H_
- #define THIRD_PARTY_FDLIBM_OVERFLOWING_MATH_H_
- #include <stdint.h>
- #include <cmath>
- #include <type_traits>
- namespace fdlibm {
- // Helpers for performing overflowing arithmetic operations without relying
- // on C++ undefined behavior.
- #define ASSERT_SIGNED_INTEGER_TYPE(Type) \
- static_assert(std::is_integral<Type>::value && std::is_signed<Type>::value, \
- "use this for signed integer types");
- #define OP_WITH_WRAPAROUND(Name, OP) \
- template <typename signed_type> \
- inline signed_type Name##WithWraparound(signed_type a, signed_type b) { \
- ASSERT_SIGNED_INTEGER_TYPE(signed_type); \
- using unsigned_type = typename std::make_unsigned<signed_type>::type; \
- unsigned_type a_unsigned = static_cast<unsigned_type>(a); \
- unsigned_type b_unsigned = static_cast<unsigned_type>(b); \
- unsigned_type result = a_unsigned OP b_unsigned; \
- return static_cast<signed_type>(result); \
- }
- OP_WITH_WRAPAROUND(Add, +)
- OP_WITH_WRAPAROUND(Sub, -)
- OP_WITH_WRAPAROUND(Mul, *)
- // 16-bit integers are special due to C++'s implicit conversion rules.
- // See https://bugs.llvm.org/show_bug.cgi?id=25580.
- template <>
- inline int16_t MulWithWraparound(int16_t a, int16_t b) {
- uint32_t a_unsigned = static_cast<uint32_t>(a);
- uint32_t b_unsigned = static_cast<uint32_t>(b);
- uint32_t result = a_unsigned * b_unsigned;
- return static_cast<int16_t>(static_cast<uint16_t>(result));
- }
- #undef OP_WITH_WRAPAROUND
- template <typename signed_type>
- inline signed_type NegateWithWraparound(signed_type a) {
- ASSERT_SIGNED_INTEGER_TYPE(signed_type);
- if (a == std::numeric_limits<signed_type>::min()) return a;
- return -a;
- }
- template <typename signed_type>
- inline signed_type ShlWithWraparound(signed_type a, signed_type b) {
- ASSERT_SIGNED_INTEGER_TYPE(signed_type);
- using unsigned_type = typename std::make_unsigned<signed_type>::type;
- const unsigned_type kMask = (sizeof(a) * 8) - 1;
- return static_cast<signed_type>(static_cast<unsigned_type>(a) << (b & kMask));
- }
- #undef ASSERT_SIGNED_INTEGER_TYPE
- // Returns the quotient x/y, avoiding C++ undefined behavior if y == 0.
- template <typename T>
- inline T Divide(T x, T y) {
- if (y != 0) return x / y;
- if (x == 0 || x != x) return std::numeric_limits<T>::quiet_NaN();
- if ((x >= 0) == (std::signbit(y) == 0)) {
- return std::numeric_limits<T>::infinity();
- }
- return -std::numeric_limits<T>::infinity();
- }
- inline float Recip(float a) { return Divide(1.0f, a); }
- inline float RecipSqrt(float a) {
- if (a != 0) return 1.0f / std::sqrt(a);
- if (std::signbit(a) == 0) return std::numeric_limits<float>::infinity();
- return -std::numeric_limits<float>::infinity();
- }
- template <typename T>
- inline T RoundingAverageUnsigned(T a, T b) {
- static_assert(std::is_unsigned<T>::value, "Only for unsiged types");
- static_assert(sizeof(T) < sizeof(uint64_t), "Must be smaller than uint64_t");
- return (static_cast<uint64_t>(a) + static_cast<uint64_t>(b) + 1) >> 1;
- }
- } // namespace fdlibm
- #endif // THIRD_PARTY_FDLIBM_OVERFLOWING_MATH_H_
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