99 lines
2.4 KiB
C++
99 lines
2.4 KiB
C++
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/* ========================================================================
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(C) Copyright 2023 by Molly Rocket, Inc., All Rights Reserved.
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Please see https://computerenhance.com for more information
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======================================================================== */
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/* ========================================================================
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LISTING 74
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======================================================================== */
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#if _WIN32
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#include <intrin.h>
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#include <windows.h>
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static u64 GetOSTimerFreq(void)
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{
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LARGE_INTEGER Freq;
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QueryPerformanceFrequency(&Freq);
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return Freq.QuadPart;
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}
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static u64 ReadOSTimer(void)
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{
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LARGE_INTEGER Value;
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QueryPerformanceCounter(&Value);
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return Value.QuadPart;
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}
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#else
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#include <x86intrin.h>
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#include <sys/time.h>
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static u64 GetOSTimerFreq(void)
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{
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return 1000000;
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}
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static u64 ReadOSTimer(void)
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{
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// NOTE(casey): The "struct" keyword is not necessary here when compiling in C++,
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// but just in case anyone is using this file from C, I include it.
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struct timeval Value;
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gettimeofday(&Value, 0);
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u64 Result = GetOSTimerFreq()*(u64)Value.tv_sec + (u64)Value.tv_usec;
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return Result;
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}
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#endif
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/* NOTE(casey): This does not need to be "inline", it could just be "static"
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because compilers will inline it anyway. But compilers will warn about
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static functions that aren't used. So "inline" is just the simplest way
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to tell them to stop complaining about that. */
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inline u64 ReadCPUTimer(void)
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{
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// NOTE(casey): If you were on ARM, you would need to replace __rdtsc
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// with one of their performance counter read instructions, depending
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// on which ones are available on your platform.
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return __rdtsc();
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}
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static u64 EstimateCPUTimerFreq(void)
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{
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u64 MillisecondsToWait = 100;
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u64 OSFreq = GetOSTimerFreq();
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u64 CPUStart = ReadCPUTimer();
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u64 OSStart = ReadOSTimer();
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u64 OSEnd = 0;
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u64 OSElapsed = 0;
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u64 OSWaitTime = OSFreq * MillisecondsToWait / 1000;
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while(OSElapsed < OSWaitTime)
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{
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OSEnd = ReadOSTimer();
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OSElapsed = OSEnd - OSStart;
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}
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u64 CPUEnd = ReadCPUTimer();
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u64 CPUElapsed = CPUEnd - CPUStart;
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u64 CPUFreq = 0;
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if(OSElapsed)
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{
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CPUFreq = OSFreq * CPUElapsed / OSElapsed;
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}
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return CPUFreq;
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}
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