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author | 2017-09-19 16:54:40 -0400 | |
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committer | 2017-09-19 16:54:40 -0400 | |
commit | c2e754829628d1e9b7a16b3389cfdace76950fdf (patch) | |
tree | 5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/base/internal/cycleclock.cc |
Initial Commit
Diffstat (limited to 'absl/base/internal/cycleclock.cc')
-rw-r--r-- | absl/base/internal/cycleclock.cc | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc new file mode 100644 index 00000000..a742df01 --- /dev/null +++ b/absl/base/internal/cycleclock.cc @@ -0,0 +1,81 @@ +// 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 +// +// http://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. + +// The implementation of CycleClock::Frequency. +// +// NOTE: only i386 and x86_64 have been well tested. +// PPC, sparc, alpha, and ia64 are based on +// http://peter.kuscsik.com/wordpress/?p=14 +// with modifications by m3b. See also +// https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h + +#include "absl/base/internal/cycleclock.h" + +#include <chrono> // NOLINT(build/c++11) + +#include "absl/base/internal/unscaledcycleclock.h" + +namespace absl { +namespace base_internal { + +#if ABSL_USE_UNSCALED_CYCLECLOCK + +namespace { + +#ifdef NDEBUG +#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY +// Not debug mode and the UnscaledCycleClock frequency is the CPU +// frequency. Scale the CycleClock to prevent overflow if someone +// tries to represent the time as cycles since the Unix epoch. +static constexpr int32_t kShift = 1; +#else +// Not debug mode and the UnscaledCycleClock isn't operating at the +// raw CPU frequency. There is no need to do any scaling, so don't +// needlessly sacrifice precision. +static constexpr int32_t kShift = 0; +#endif +#else +// In debug mode use a different shift to discourage depending on a +// particular shift value. +static constexpr int32_t kShift = 2; +#endif + +static constexpr double kFrequencyScale = 1.0 / (1 << kShift); + +} // namespace + +int64_t CycleClock::Now() { + return base_internal::UnscaledCycleClock::Now() >> kShift; +} + +double CycleClock::Frequency() { + return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency(); +} + +#else + +int64_t CycleClock::Now() { + return std::chrono::duration_cast<std::chrono::nanoseconds>( + std::chrono::steady_clock::now().time_since_epoch()) + .count(); +} + +double CycleClock::Frequency() { + return 1e9; +} + +#endif + +} // namespace base_internal +} // namespace absl |