a15364ce4d
-- d35c72d705155dcd89a92835103540f14c643d10 by Gennadiy Rozental <rogeeff@google.com>: helpxml changed to report types of flags with built-in value type. PiperOrigin-RevId: 275131440 -- f3478792943d7dd40a6ef6083a8e5d374f43a65e by Abseil Team <absl-team@google.com>: Add space padding tests for hex conversions. PiperOrigin-RevId: 275120155 -- 7c2e4725403e173660f33f94af686a75d3722936 by Andy Soffer <asoffer@google.com>: Fix https://github.com/abseil/abseil-cpp/issues/379 by renaming `roundup` to `round_up` PiperOrigin-RevId: 275106110 -- 84cb30d6ee509961ac4359cfdda1360973b9527d by Laramie Leavitt <lar@google.com>: Move random_internal::wide_multiply into a file by the same name. PiperOrigin-RevId: 275059359 -- 06d691a8c187b5d899e7863784b23bdcfd580cb2 by Abseil Team <absl-team@google.com>: Add missing "return" keyword. PiperOrigin-RevId: 275036408 GitOrigin-RevId: d35c72d705155dcd89a92835103540f14c643d10 Change-Id: Id837b4de6c9cfe18f0a088363754bfe389df985b
109 lines
3.7 KiB
C++
109 lines
3.7 KiB
C++
// 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/base/internal/bits.h"
|
|
#include "absl/numeric/int128.h"
|
|
#include "absl/random/internal/traits.h"
|
|
|
|
namespace absl {
|
|
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 uint128 MultiplyU64ToU128(uint64_t a, uint64_t b) {
|
|
#if defined(ABSL_HAVE_INTRINSIC_INT128)
|
|
return 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 = uint128;
|
|
|
|
static result_type multiply(uint64_t a, uint64_t b) {
|
|
return MultiplyU64ToU128(a, b);
|
|
}
|
|
|
|
static uint64_t hi(result_type r) { return Uint128High64(r); }
|
|
static uint64_t lo(result_type r) { return Uint128Low64(r); }
|
|
};
|
|
#endif
|
|
|
|
} // namespace random_internal
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_
|