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Revert "<chrono>: Cache QueryPerformanceFrequency() and divide just o… #972

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Merged
StephanTLavavej merged 3 commits into from
Jul 3, 2020
Merged

Revert "<chrono>: Cache QueryPerformanceFrequency() and divide just o… #972

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8c360df
Revert "<chrono>: Cache QueryPerformanceFrequency() and divide just o…
AlexGuteniev Jul 2, 2020
c446067
reverted too much
AlexGuteniev Jul 2, 2020
35c5406
Remove push/disable in addition to pop.
StephanTLavavej Jul 2, 2020
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39 changes: 1 addition & 38 deletions stl/inc/chrono
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,6 @@
#include <ratio>
#include <time.h>
#include <utility>
#include <xatomic.h>
#include <xtimec.h>

#pragma pack(push, _CRT_PACKING)
Expand Down Expand Up @@ -604,45 +603,9 @@ namespace chrono {
using time_point = chrono::time_point<steady_clock>;
static constexpr bool is_steady = true;

#pragma warning(push)
#pragma warning(disable : 28112) // A variable which is accessed via an Interlocked function must
// always be accessed via an Interlocked function.
_NODISCARD static time_point now() noexcept { // get current time
#if (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM) || defined(_M_ARM64)) && !defined(_M_CEE_PURE)
// Implement atomics avoiding <atomic> header dependency
static volatile long long _Cached_freq = LLONG_MAX;
static volatile long long _Cached_ctr_base = LLONG_MAX;
static volatile long long _Cached_result_base = LLONG_MAX;

const long long _Freq_from_cache = _Atomic_load_ll_relaxed(&_Cached_freq);
const long long _Ctr_base = _Atomic_load_ll_relaxed(&_Cached_ctr_base);
const long long _Result_base = _Atomic_load_ll_relaxed(&_Cached_result_base);
if (_Freq_from_cache != LLONG_MAX && _Ctr_base != LLONG_MAX && _Result_base != LLONG_MAX) {
// Fast path
const long long _Ctr = _Query_perf_counter();
return time_point(duration(_Result_base + (_Ctr - _Ctr_base) * period::den / _Freq_from_cache));
}
// Calculate with two divisions to prevent overflow
const long long _Freq = _Query_perf_frequency();
const long long _Ctr = _Query_perf_counter();
const long long _Result = _Scale_large_counter(_Ctr, _Freq);
if (_InterlockedCompareExchange64(&_Cached_freq, _Freq, LLONG_MAX) == LLONG_MAX) {
// This is the first result, save current result as base for fast path
_InterlockedCompareExchange64(&_Cached_ctr_base, _Ctr, LLONG_MAX);
_InterlockedCompareExchange64(&_Cached_result_base, _Result, LLONG_MAX);
}
// if _Result is not saved as first, it is still compatible with fast result
return time_point(duration(_Result));
#else // ^^^ known hardware && !defined(_M_CEE_PURE) / unknown hardware || defined(_M_CEE_PURE) vvv
const long long _Freq = _Query_perf_frequency(); // doesn't change after system boot
const long long _Ctr = _Query_perf_counter();
return time_point(duration(_Scale_large_counter(_Ctr, _Freq)));
#endif // (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM) || defined(_M_ARM64)) && !defined(_M_CEE_PURE)
}
#pragma warning(pop)

private:
_NODISCARD static long long _Scale_large_counter(const long long _Ctr, const long long _Freq) noexcept {
static_assert(period::num == 1, "This assumes period::num == 1.");
// Instead of just having "(_Ctr * period::den) / _Freq",
// the algorithm below prevents overflow when _Ctr is sufficiently large.
Expand All @@ -651,7 +614,7 @@ namespace chrono {
// but the initial value of _Ctr could be large.
const long long _Whole = (_Ctr / _Freq) * period::den;
const long long _Part = (_Ctr % _Freq) * period::den / _Freq;
return _Whole + _Part;
return time_point(duration(_Whole + _Part));
}
};

Expand Down
12 changes: 0 additions & 12 deletions stl/inc/xatomic.h
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Original file line number Diff line number Diff line change
Expand Up @@ -101,18 +101,6 @@ _NODISCARD const volatile _Integral* _Atomic_address_as(const _Ty& _Source) noex
return &reinterpret_cast<const volatile _Integral&>(_Source);
}

// FUNCTION TEMPLATE _Atomic_load_ll_relaxed
#if (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM) || defined(_M_ARM64)) && !defined(_M_CEE_PURE)
_NODISCARD inline long long _Atomic_load_ll_relaxed(volatile long long* _Mem) noexcept {
// Copy from _Atomic_storage<_Ty, 8>::load
#ifdef _M_ARM
return __ldrexd(_Mem);
#else
return __iso_volatile_load64(_Mem);
#endif
}
#endif // (defined(_M_IX86) || defined(_M_X64) || defined(_M_ARM) || defined(_M_ARM64)) && !defined(_M_CEE_PURE)

_STD_END

#pragma pop_macro("new")
Expand Down