12bc53e031
-- c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>: Remove a floating point division by zero test. This isn't testing behavior related to the library, and MSVC warns about it in opt mode. PiperOrigin-RevId: 285220804 -- 68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>: This CL introduces following changes to the class FlagImpl: * We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately. * CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now. * Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call. * We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced. PiperOrigin-RevId: 285132636 -- ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>: Change null-term* (and nul-term*) to NUL-term* in comments PiperOrigin-RevId: 285036610 -- 729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>: Use the Posix implementation of thread identity on MinGW. Some versions of MinGW suffer from thread_local bugs. PiperOrigin-RevId: 285022920 -- 39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>: Implementation detail change. Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil. PiperOrigin-RevId: 285012012 GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1
74 lines
2.5 KiB
C++
74 lines
2.5 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_RANDOM_INTERNAL_FASTMATH_H_
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#define ABSL_RANDOM_INTERNAL_FASTMATH_H_
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// This file contains fast math functions (bitwise ops as well as some others)
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// which are implementation details of various absl random number distributions.
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#include <cassert>
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#include <cmath>
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#include <cstdint>
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#include "absl/base/internal/bits.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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// Returns the position of the first bit set.
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inline int LeadingSetBit(uint64_t n) {
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return 64 - base_internal::CountLeadingZeros64(n);
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}
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// Compute log2(n) using integer operations.
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// While std::log2 is more accurate than std::log(n) / std::log(2), for
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// very large numbers--those close to std::numeric_limits<uint64_t>::max() - 2,
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// for instance--std::log2 rounds up rather than down, which introduces
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// definite skew in the results.
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inline int IntLog2Floor(uint64_t n) {
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return (n <= 1) ? 0 : (63 - base_internal::CountLeadingZeros64(n));
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}
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inline int IntLog2Ceil(uint64_t n) {
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return (n <= 1) ? 0 : (64 - base_internal::CountLeadingZeros64(n - 1));
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}
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inline double StirlingLogFactorial(double n) {
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assert(n >= 1);
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// Using Stirling's approximation.
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constexpr double kLog2PI = 1.83787706640934548356;
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const double logn = std::log(n);
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const double ninv = 1.0 / static_cast<double>(n);
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return n * logn - n + 0.5 * (kLog2PI + logn) + (1.0 / 12.0) * ninv -
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(1.0 / 360.0) * ninv * ninv * ninv;
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}
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// Rotate value right.
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//
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// We only implement the uint32_t / uint64_t versions because
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// 1) those are the only ones we use, and
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// 2) those are the only ones where clang detects the rotate idiom correctly.
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inline constexpr uint32_t rotr(uint32_t value, uint8_t bits) {
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return (value >> (bits & 31)) | (value << ((-bits) & 31));
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}
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inline constexpr uint64_t rotr(uint64_t value, uint8_t bits) {
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return (value >> (bits & 63)) | (value << ((-bits) & 63));
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}
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_FASTMATH_H_
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