1e39f8626a
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b842b7fd9b1289be31f0b7ee8e62e48e550747cf by Greg Falcon <gfalcon@google.com>:
Change the Cord str_format formatter to use iteration instead of CordReader.
When Cord is publicly released, CordReader is not going with it.
PiperOrigin-RevId: 284780736
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28e76c08ea7185a7ff9f4e0e02ae565fbbf7980f by Greg Falcon <gfalcon@google.com>:
Implementation detail change.
Introduce ABSL_NAMESPACE_BEGIN and _END annotation macros which indicate the beginning and end of a `namespace absl` scope. Currently these do nothing, but they will be used to inject an inline namespace for LTS builds (to avoid symbol collisions against other Abseil versions).
These macros should not be used by end users, because end users should never write `namespace absl {` in their own code.
This CL applies these annotations to all code under //absl/base/. The rest of Abseil will be annotated in this way in follow-up CLs.
PiperOrigin-RevId: 284776410
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e1711dc6d696dcca50d4e7d4b4d8f3076575b7ec by Abseil Team <absl-team@google.com>:
--help changed to report long flags.
PiperOrigin-RevId: 284757720
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78f66a68f428bbbd19d8d60e1125f43ba765fd35 by Tom Manshreck <shreck@google.com>:
Update comment on + or - in SimpleAToi()
PiperOrigin-RevId: 284231843
GitOrigin-RevId: b842b7fd9b1289be31f0b7ee8e62e48e550747cf
Change-Id: I3046b31391bd11c8bc4abab7785a863c377cd757
107 lines
3.3 KiB
C++
107 lines
3.3 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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// The implementation of CycleClock::Frequency.
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//
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// NOTE: only i386 and x86_64 have been well tested.
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// PPC, sparc, alpha, and ia64 are based on
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// http://peter.kuscsik.com/wordpress/?p=14
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// with modifications by m3b. See also
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// https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h
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#include "absl/base/internal/cycleclock.h"
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#include <atomic>
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#include <chrono> // NOLINT(build/c++11)
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#include "absl/base/internal/unscaledcycleclock.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace base_internal {
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#if ABSL_USE_UNSCALED_CYCLECLOCK
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namespace {
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#ifdef NDEBUG
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#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
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// Not debug mode and the UnscaledCycleClock frequency is the CPU
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// frequency. Scale the CycleClock to prevent overflow if someone
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// tries to represent the time as cycles since the Unix epoch.
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static constexpr int32_t kShift = 1;
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#else
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// Not debug mode and the UnscaledCycleClock isn't operating at the
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// raw CPU frequency. There is no need to do any scaling, so don't
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// needlessly sacrifice precision.
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static constexpr int32_t kShift = 0;
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#endif
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#else
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// In debug mode use a different shift to discourage depending on a
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// particular shift value.
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static constexpr int32_t kShift = 2;
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#endif
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static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
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static std::atomic<CycleClockSourceFunc> cycle_clock_source;
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CycleClockSourceFunc LoadCycleClockSource() {
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// Optimize for the common case (no callback) by first doing a relaxed load;
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// this is significantly faster on non-x86 platforms.
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if (cycle_clock_source.load(std::memory_order_relaxed) == nullptr) {
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return nullptr;
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}
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// This corresponds to the store(std::memory_order_release) in
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// CycleClockSource::Register, and makes sure that any updates made prior to
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// registering the callback are visible to this thread before the callback is
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// invoked.
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return cycle_clock_source.load(std::memory_order_acquire);
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}
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} // namespace
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int64_t CycleClock::Now() {
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auto fn = LoadCycleClockSource();
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if (fn == nullptr) {
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return base_internal::UnscaledCycleClock::Now() >> kShift;
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}
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return fn() >> kShift;
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}
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double CycleClock::Frequency() {
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return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
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}
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void CycleClockSource::Register(CycleClockSourceFunc source) {
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// Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
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cycle_clock_source.store(source, std::memory_order_release);
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}
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#else
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int64_t CycleClock::Now() {
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return std::chrono::duration_cast<std::chrono::nanoseconds>(
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std::chrono::steady_clock::now().time_since_epoch())
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.count();
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}
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double CycleClock::Frequency() {
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return 1e9;
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}
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#endif
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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