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7835e5802a
Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.
`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.
Compared to macro-based include guards, `#pragma once`:
- Eliminates the risk of macro name collisions or copy/paste errors
where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
(e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
file entirely, rather than re-reading it to find the matching
`#endif` ("multiple-include optimization").
- Note that some compilers may already optimize traditional include
guards, by recognzining the idiomatic pattern.
This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.
However, this is considered acceptable given:
1. edk2 already defines a subset of supported compilers in
BaseTools/Conf/tools_def.template, all of which have supported
`#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
include guard naming and potential macro collisions.
Approximate compiler support dates:
- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
(http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
105 lines
3 KiB
C
105 lines
3 KiB
C
/** @file
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Provides calibrated delay and performance counter services.
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Copyright (c) 2006 - 2011, Intel Corporation. All rights reserved.<BR>
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SPDX-License-Identifier: BSD-2-Clause-Patent
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**/
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#pragma once
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/**
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Stalls the CPU for at least the given number of microseconds.
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Stalls the CPU for the number of microseconds specified by MicroSeconds.
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@param MicroSeconds The minimum number of microseconds to delay.
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@return The value of MicroSeconds inputted.
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**/
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UINTN
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EFIAPI
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MicroSecondDelay (
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IN UINTN MicroSeconds
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);
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/**
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Stalls the CPU for at least the given number of nanoseconds.
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Stalls the CPU for the number of nanoseconds specified by NanoSeconds.
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@param NanoSeconds The minimum number of nanoseconds to delay.
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@return The value of NanoSeconds inputted.
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**/
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UINTN
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EFIAPI
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NanoSecondDelay (
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IN UINTN NanoSeconds
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);
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/**
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Retrieves the current value of a 64-bit free running performance counter.
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The counter can either count up by 1 or count down by 1. If the physical
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performance counter counts by a larger increment, then the counter values
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must be translated. The properties of the counter can be retrieved from
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GetPerformanceCounterProperties().
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@return The current value of the free running performance counter.
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**/
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UINT64
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EFIAPI
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GetPerformanceCounter (
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VOID
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);
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/**
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Retrieves the 64-bit frequency in Hz and the range of performance counter
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values.
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If StartValue is not NULL, then the value that the performance counter starts
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with immediately after is it rolls over is returned in StartValue. If
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EndValue is not NULL, then the value that the performance counter end with
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immediately before it rolls over is returned in EndValue. The 64-bit
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frequency of the performance counter in Hz is always returned. If StartValue
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is less than EndValue, then the performance counter counts up. If StartValue
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is greater than EndValue, then the performance counter counts down. For
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example, a 64-bit free running counter that counts up would have a StartValue
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of 0 and an EndValue of 0xFFFFFFFFFFFFFFFF. A 24-bit free running counter
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that counts down would have a StartValue of 0xFFFFFF and an EndValue of 0.
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@param StartValue The value the performance counter starts with when it
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rolls over.
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@param EndValue The value that the performance counter ends with before
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it rolls over.
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@return The frequency in Hz.
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**/
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UINT64
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EFIAPI
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GetPerformanceCounterProperties (
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OUT UINT64 *StartValue OPTIONAL,
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OUT UINT64 *EndValue OPTIONAL
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);
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/**
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Converts elapsed ticks of performance counter to time in nanoseconds.
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This function converts the elapsed ticks of running performance counter to
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time value in unit of nanoseconds.
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@param Ticks The number of elapsed ticks of running performance counter.
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@return The elapsed time in nanoseconds.
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**/
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UINT64
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EFIAPI
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GetTimeInNanoSecond (
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IN UINT64 Ticks
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);
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