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Diffstat (limited to 'absl/random/internal/distribution_impl.h')
| -rw-r--r-- | absl/random/internal/distribution_impl.h | 262 |
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diff --git a/absl/random/internal/distribution_impl.h b/absl/random/internal/distribution_impl.h deleted file mode 100644 index a8e5d61e..00000000 --- a/absl/random/internal/distribution_impl.h +++ /dev/null @@ -1,262 +0,0 @@ -// 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_DISTRIBUTION_IMPL_H_ -#define ABSL_RANDOM_INTERNAL_DISTRIBUTION_IMPL_H_ - -// This file contains some implementation details which are used by one or more -// of the absl random number distributions. - -#include <cfloat> -#include <cstddef> -#include <cstdint> -#include <cstring> -#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/fastmath.h" -#include "absl/random/internal/traits.h" - -namespace absl { -inline namespace lts_2019_08_08 { -namespace random_internal { - -// Creates a double from `bits`, with the template fields controlling the -// output. -// -// RandU64To is both more efficient and generates more unique values in the -// result interval than known implementations of std::generate_canonical(). -// -// The `Signed` parameter controls whether positive, negative, or both are -// returned (thus affecting the output interval). -// When Signed == SignedValueT, range is U(-1, 1) -// When Signed == NegativeValueT, range is U(-1, 0) -// When Signed == PositiveValueT, range is U(0, 1) -// -// When the `IncludeZero` parameter is true, the function may return 0 for some -// inputs, otherwise it never returns 0. -// -// The `ExponentBias` parameter determines the scale of the output range by -// adjusting the exponent. -// -// When a value in U(0,1) is required, use: -// RandU64ToDouble<PositiveValueT, true, 0>(); -// -// When a value in U(-1,1) is required, use: -// RandU64ToDouble<SignedValueT, false, 0>() => U(-1, 1) -// This generates more distinct values than the mathematically equivalent -// expression `U(0, 1) * 2.0 - 1.0`, and is preferable. -// -// Scaling the result by powers of 2 (and avoiding a multiply) is also possible: -// RandU64ToDouble<PositiveValueT, false, 1>(); => U(0, 2) -// RandU64ToDouble<PositiveValueT, false, -1>(); => U(0, 0.5) -// - -// Tristate types controlling the output. -struct PositiveValueT {}; -struct NegativeValueT {}; -struct SignedValueT {}; - -// RandU64ToDouble is the double-result variant of RandU64To, described above. -template <typename Signed, bool IncludeZero, int ExponentBias = 0> -inline double RandU64ToDouble(uint64_t bits) { - static_assert(std::is_same<Signed, PositiveValueT>::value || - std::is_same<Signed, NegativeValueT>::value || - std::is_same<Signed, SignedValueT>::value, - ""); - - // Maybe use the left-most bit for a sign bit. - uint64_t sign = std::is_same<Signed, NegativeValueT>::value - ? 0x8000000000000000ull - : 0; // Sign bits. - - if (std::is_same<Signed, SignedValueT>::value) { - sign = bits & 0x8000000000000000ull; - bits = bits & 0x7FFFFFFFFFFFFFFFull; - } - if (IncludeZero) { - if (bits == 0u) return 0; - } - - // Number of leading zeros is mapped to the exponent: 2^-clz - int clz = base_internal::CountLeadingZeros64(bits); - // Shift number left to erase leading zeros. - bits <<= IncludeZero ? clz : (clz & 63); - - // Shift number right to remove bits that overflow double mantissa. The - // direction of the shift depends on `clz`. - bits >>= (64 - DBL_MANT_DIG); - - // Compute IEEE 754 double exponent. - // In the Signed case, bits is a 63-bit number with a 0 msb. Adjust the - // exponent to account for that. - const uint64_t exp = - (std::is_same<Signed, SignedValueT>::value ? 1023U : 1022U) + - static_cast<uint64_t>(ExponentBias - clz); - constexpr int kExp = DBL_MANT_DIG - 1; - // Construct IEEE 754 double from exponent and mantissa. - const uint64_t val = sign | (exp << kExp) | (bits & ((1ULL << kExp) - 1U)); - - double res; - static_assert(sizeof(res) == sizeof(val), "double is not 64 bit"); - // Memcpy value from "val" to "res" to avoid aliasing problems. Assumes that - // endian-ness is same for double and uint64_t. - std::memcpy(&res, &val, sizeof(res)); - - return res; -} - -// RandU64ToFloat is the float-result variant of RandU64To, described above. -template <typename Signed, bool IncludeZero, int ExponentBias = 0> -inline float RandU64ToFloat(uint64_t bits) { - static_assert(std::is_same<Signed, PositiveValueT>::value || - std::is_same<Signed, NegativeValueT>::value || - std::is_same<Signed, SignedValueT>::value, - ""); - - // Maybe use the left-most bit for a sign bit. - uint64_t sign = std::is_same<Signed, NegativeValueT>::value - ? 0x80000000ul - : 0; // Sign bits. - - if (std::is_same<Signed, SignedValueT>::value) { - uint64_t a = bits & 0x8000000000000000ull; - sign = static_cast<uint32_t>(a >> 32); - bits = bits & 0x7FFFFFFFFFFFFFFFull; - } - if (IncludeZero) { - if (bits == 0u) return 0; - } - - // Number of leading zeros is mapped to the exponent: 2^-clz - int clz = base_internal::CountLeadingZeros64(bits); - // Shift number left to erase leading zeros. - bits <<= IncludeZero ? clz : (clz & 63); - // Shift number right to remove bits that overflow double mantissa. The - // direction of the shift depends on `clz`. - bits >>= (64 - FLT_MANT_DIG); - - // Construct IEEE 754 float exponent. - // In the Signed case, bits is a 63-bit number with a 0 msb. Adjust the - // exponent to account for that. - const uint32_t exp = - (std::is_same<Signed, SignedValueT>::value ? 127U : 126U) + - static_cast<uint32_t>(ExponentBias - clz); - constexpr int kExp = FLT_MANT_DIG - 1; - const uint32_t val = sign | (exp << kExp) | (bits & ((1U << kExp) - 1U)); - - float res; - static_assert(sizeof(res) == sizeof(val), "float is not 32 bit"); - // Assumes that endian-ness is same for float and uint32_t. - std::memcpy(&res, &val, sizeof(res)); - - return res; -} - -template <typename Result> -struct RandU64ToReal { - template <typename Signed, bool IncludeZero, int ExponentBias = 0> - static inline Result Value(uint64_t bits) { - return RandU64ToDouble<Signed, IncludeZero, ExponentBias>(bits); - } -}; - -template <> -struct RandU64ToReal<float> { - template <typename Signed, bool IncludeZero, int ExponentBias = 0> - static inline float Value(uint64_t bits) { - return RandU64ToFloat<Signed, IncludeZero, ExponentBias>(bits); - } -}; - -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 -} // inline namespace lts_2019_08_08 -} // namespace absl - -#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTION_IMPL_H_ |