base/internal/cycleclock_config.h

0001 // Copyright 2022 The Abseil Authors
0002 //
0003 // Licensed under the Apache License, Version 2.0 (the "License");
0004 // you may not use this file except in compliance with the License.
0005 // You may obtain a copy of the License at
0006 //
0007 //     https://www.apache.org/licenses/LICENSE-2.0
0008 //
0009 // Unless required by applicable law or agreed to in writing, software
0010 // distributed under the License is distributed on an "AS IS" BASIS,
0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0012 // See the License for the specific language governing permissions and
0013 // limitations under the License.
0014
0015 #ifndef ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_
0016 #define ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_
0017
0018 #include <cstdint>
0019
0020 #include "absl/base/config.h"
0021 #include "absl/base/internal/inline_variable.h"
0022 #include "absl/base/internal/unscaledcycleclock_config.h"
0023
0024 namespace absl {
0025 ABSL_NAMESPACE_BEGIN
0026 namespace base_internal {
0027
0028 #if ABSL_USE_UNSCALED_CYCLECLOCK
0029 #ifdef NDEBUG
0030 #ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
0031 // Not debug mode and the UnscaledCycleClock frequency is the CPU
0032 // frequency.  Scale the CycleClock to prevent overflow if someone
0033 // tries to represent the time as cycles since the Unix epoch.
0034 ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 1);
0035 #else
0036 // Not debug mode and the UnscaledCycleClock isn't operating at the
0037 // raw CPU frequency. There is no need to do any scaling, so don't
0038 // needlessly sacrifice precision.
0039 ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 0);
0040 #endif
0041 #else   // NDEBUG
0042 // In debug mode use a different shift to discourage depending on a
0043 // particular shift value.
0044 ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 2);
0045 #endif  // NDEBUG
0046
0047 ABSL_INTERNAL_INLINE_CONSTEXPR(double, kCycleClockFrequencyScale,
0048                                1.0 / (1 << kCycleClockShift));
0049 #endif  //  ABSL_USE_UNSCALED_CYCLECLOC
0050
0051 }  // namespace base_internal
0052 ABSL_NAMESPACE_END
0053 }  // namespace absl
0054
0055 #endif  // ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_