| // Copyright 2017 The Abseil Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| #ifndef ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_ |
| #define ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_ |
| |
| #include <cstdint> |
| #include <limits> |
| #include <type_traits> |
| |
| #if (defined(_WIN32) || defined(_WIN64)) && defined(_M_IA64) |
| #include <intrin.h> // NOLINT(build/include_order) |
| #pragma intrinsic(_umul128) |
| #define ABSL_INTERNAL_USE_UMUL128 1 |
| #endif |
| |
| #include "absl/base/config.h" |
| #include "absl/numeric/bits.h" |
| #include "absl/numeric/int128.h" |
| #include "absl/random/internal/traits.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace random_internal { |
| |
| // Helper object to multiply two 64-bit values to a 128-bit value. |
| // MultiplyU64ToU128 multiplies two 64-bit values to a 128-bit value. |
| // If an intrinsic is available, it is used, otherwise use native 32-bit |
| // multiplies to construct the result. |
| inline absl::uint128 MultiplyU64ToU128(uint64_t a, uint64_t b) { |
| #if defined(ABSL_HAVE_INTRINSIC_INT128) |
| return absl::uint128(static_cast<__uint128_t>(a) * b); |
| #elif defined(ABSL_INTERNAL_USE_UMUL128) |
| // uint64_t * uint64_t => uint128 multiply using imul intrinsic on MSVC. |
| uint64_t high = 0; |
| const uint64_t low = _umul128(a, b, &high); |
| return absl::MakeUint128(high, low); |
| #else |
| // uint128(a) * uint128(b) in emulated mode computes a full 128-bit x 128-bit |
| // multiply. However there are many cases where that is not necessary, and it |
| // is only necessary to support a 64-bit x 64-bit = 128-bit multiply. This is |
| // for those cases. |
| const uint64_t a00 = static_cast<uint32_t>(a); |
| const uint64_t a32 = a >> 32; |
| const uint64_t b00 = static_cast<uint32_t>(b); |
| const uint64_t b32 = b >> 32; |
| |
| const uint64_t c00 = a00 * b00; |
| const uint64_t c32a = a00 * b32; |
| const uint64_t c32b = a32 * b00; |
| const uint64_t c64 = a32 * b32; |
| |
| const uint32_t carry = |
| static_cast<uint32_t>(((c00 >> 32) + static_cast<uint32_t>(c32a) + |
| static_cast<uint32_t>(c32b)) >> |
| 32); |
| |
| return absl::MakeUint128(c64 + (c32a >> 32) + (c32b >> 32) + carry, |
| c00 + (c32a << 32) + (c32b << 32)); |
| #endif |
| } |
| |
| // wide_multiply<T> multiplies two N-bit values to a 2N-bit result. |
| template <typename UIntType> |
| struct wide_multiply { |
| static constexpr size_t kN = std::numeric_limits<UIntType>::digits; |
| using input_type = UIntType; |
| using result_type = typename random_internal::unsigned_bits<kN * 2>::type; |
| |
| static result_type multiply(input_type a, input_type b) { |
| return static_cast<result_type>(a) * b; |
| } |
| |
| static input_type hi(result_type r) { return r >> kN; } |
| static input_type lo(result_type r) { return r; } |
| |
| static_assert(std::is_unsigned<UIntType>::value, |
| "Class-template wide_multiply<> argument must be unsigned."); |
| }; |
| |
| #ifndef ABSL_HAVE_INTRINSIC_INT128 |
| template <> |
| struct wide_multiply<uint64_t> { |
| using input_type = uint64_t; |
| using result_type = absl::uint128; |
| |
| static result_type multiply(uint64_t a, uint64_t b) { |
| return MultiplyU64ToU128(a, b); |
| } |
| |
| static uint64_t hi(result_type r) { return absl::Uint128High64(r); } |
| static uint64_t lo(result_type r) { return absl::Uint128Low64(r); } |
| }; |
| #endif |
| |
| } // namespace random_internal |
| ABSL_NAMESPACE_END |
| } // namespace absl |
| |
| #endif // ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_ |