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Diffstat (limited to 'third_party/abseil_cpp/absl/random/internal/generate_real.h')
| -rw-r--r-- | third_party/abseil_cpp/absl/random/internal/generate_real.h | 146 |
1 files changed, 0 insertions, 146 deletions
diff --git a/third_party/abseil_cpp/absl/random/internal/generate_real.h b/third_party/abseil_cpp/absl/random/internal/generate_real.h deleted file mode 100644 index 20f6d20807..0000000000 --- a/third_party/abseil_cpp/absl/random/internal/generate_real.h +++ /dev/null @@ -1,146 +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_GENERATE_REAL_H_ -#define ABSL_RANDOM_INTERNAL_GENERATE_REAL_H_ - -// This file contains some implementation details which are used by one or more -// of the absl random number distributions. - -#include <cstdint> -#include <cstring> -#include <limits> -#include <type_traits> - -#include "absl/base/internal/bits.h" -#include "absl/meta/type_traits.h" -#include "absl/random/internal/fastmath.h" -#include "absl/random/internal/traits.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace random_internal { - -// Tristate tag types controlling the output of GenerateRealFromBits. -struct GeneratePositiveTag {}; -struct GenerateNegativeTag {}; -struct GenerateSignedTag {}; - -// GenerateRealFromBits generates a single real value from a single 64-bit -// `bits` with template fields controlling the output. -// -// The `SignedTag` parameter controls whether positive, negative, -// or either signed/unsigned may be returned. -// When SignedTag == GeneratePositiveTag, range is U(0, 1) -// When SignedTag == GenerateNegativeTag, range is U(-1, 0) -// When SignedTag == GenerateSignedTag, range is U(-1, 1) -// -// When the `IncludeZero` parameter is true, the function may return 0 for some -// inputs, otherwise it never returns 0. -// -// When a value in U(0,1) is required, use: -// Uniform64ToReal<double, PositiveValueT, true>; -// -// When a value in U(-1,1) is required, use: -// Uniform64ToReal<double, SignedValueT, false>; -// -// This generates more distinct values than the mathematical equivalent -// `U(0, 1) * 2.0 - 1.0`. -// -// Scaling the result by powers of 2 (and avoiding a multiply) is also possible: -// GenerateRealFromBits<double>(..., -1); => U(0, 0.5) -// GenerateRealFromBits<double>(..., 1); => U(0, 2) -// -template <typename RealType, // Real type, either float or double. - typename SignedTag = GeneratePositiveTag, // Whether a positive, - // negative, or signed - // value is generated. - bool IncludeZero = true> -inline RealType GenerateRealFromBits(uint64_t bits, int exp_bias = 0) { - using real_type = RealType; - using uint_type = absl::conditional_t<std::is_same<real_type, float>::value, - uint32_t, uint64_t>; - - static_assert( - (std::is_same<double, real_type>::value || - std::is_same<float, real_type>::value), - "GenerateRealFromBits must be parameterized by either float or double."); - - static_assert(sizeof(uint_type) == sizeof(real_type), - "Mismatched unsinged and real types."); - - static_assert((std::numeric_limits<real_type>::is_iec559 && - std::numeric_limits<real_type>::radix == 2), - "RealType representation is not IEEE 754 binary."); - - static_assert((std::is_same<SignedTag, GeneratePositiveTag>::value || - std::is_same<SignedTag, GenerateNegativeTag>::value || - std::is_same<SignedTag, GenerateSignedTag>::value), - ""); - - static constexpr int kExp = std::numeric_limits<real_type>::digits - 1; - static constexpr uint_type kMask = (static_cast<uint_type>(1) << kExp) - 1u; - static constexpr int kUintBits = sizeof(uint_type) * 8; - - int exp = exp_bias + int{std::numeric_limits<real_type>::max_exponent - 2}; - - // Determine the sign bit. - // Depending on the SignedTag, this may use the left-most bit - // or it may be a constant value. - uint_type sign = std::is_same<SignedTag, GenerateNegativeTag>::value - ? (static_cast<uint_type>(1) << (kUintBits - 1)) - : 0; - if (std::is_same<SignedTag, GenerateSignedTag>::value) { - if (std::is_same<uint_type, uint64_t>::value) { - sign = bits & uint64_t{0x8000000000000000}; - } - if (std::is_same<uint_type, uint32_t>::value) { - const uint64_t tmp = bits & uint64_t{0x8000000000000000}; - sign = static_cast<uint32_t>(tmp >> 32); - } - // adjust the bits and the exponent to account for removing - // the leading bit. - bits = bits & uint64_t{0x7FFFFFFFFFFFFFFF}; - exp++; - } - if (IncludeZero) { - if (bits == 0u) return 0; - } - - // Number of leading zeros is mapped to the exponent: 2^-clz - // bits is 0..01xxxxxx. After shifting, we're left with 1xxx...0..0 - int clz = base_internal::CountLeadingZeros64(bits); - bits <<= (IncludeZero ? clz : (clz & 63)); // remove 0-bits. - exp -= clz; // set the exponent. - bits >>= (63 - kExp); - - // Construct the 32-bit or 64-bit IEEE 754 floating-point value from - // the individual fields: sign, exp, mantissa(bits). - uint_type val = - (std::is_same<SignedTag, GeneratePositiveTag>::value ? 0u : sign) | - (static_cast<uint_type>(exp) << kExp) | - (static_cast<uint_type>(bits) & kMask); - - // bit_cast to the output-type - real_type result; - memcpy(static_cast<void*>(&result), static_cast<const void*>(&val), - sizeof(result)); - return result; -} - -} // namespace random_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif // ABSL_RANDOM_INTERNAL_GENERATE_REAL_H_ |