cpu 주파수를 비교적 정확하게 계산하는 프로그램

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <math.h>
#include <windows.h>

static ULONGLONG g_pf_s,g_pf_e,g_sys_freq = {0};
static ULONGLONG g_cycle_s,g_cycle_passed;

// CPU        
WINAPI DWORD busy(PVOID param){for(;;);}

inline ULONGLONG rdtsc(void)
{
	ULONG hi,lo;
	__asm__ __volatile__("rdtsc;movl %%edx,%0;movl %%eax,%1":"=m"(hi),"=m"(lo));
	return (ULONGLONG)hi<<32 | lo;
}

void get_sys_freq(void)
{
	QueryPerformanceFrequency((PLARGE_INTEGER)&g_sys_freq);
}

static void start(void)
{
	QueryPerformanceCounter((PLARGE_INTEGER)&g_pf_s);
	g_cycle_s = rdtsc();
}

static void end(void)
{
	g_cycle_passed = rdtsc() - g_cycle_s;
	QueryPerformanceCounter((PLARGE_INTEGER)&g_pf_e);
}

static void sh_cpu_pf(ULONG *pmhz,double *pmhz_dbl)
{	
	//         
	ULONGLONG act_time_passed = (g_pf_e - g_pf_s) * 1000 / g_sys_freq;	
	ULONG mhz = g_cycle_passed/act_time_passed/1000;
	double mhz_dbl = (double)g_cycle_passed/act_time_passed/1000;
	printf("sleep act time is %f ms,CPU is %f(%u) MHz
",(double)act_time_passed,\
		mhz_dbl,(unsigned)mhz);
	*pmhz=mhz;*pmhz_dbl=mhz_dbl;
}

typedef struct _pf_item
{
	ULONG mhz;
	double mhz_dbl;
}pf_item,*ppf_item;

int main(int argc,char *argv[])
{	
	pf_item pf_ary[32];
	//                   
	SetThreadPriority(GetCurrentThread(),THREAD_PRIORITY_HIGHEST);
	get_sys_freq();
	
	DWORD tid;
	CreateThread(NULL,0,busy,0,0,&tid);
	Sleep(1000);
	
	ULONGLONG mhz_total = 0;
	double mhz_dbl_total = 0.0f;
	for(int i = 0;i<32;i++)
	{
		start();
		Sleep(500);
		end();
		sh_cpu_pf(&pf_ary[i].mhz,&pf_ary[i].mhz_dbl);
		mhz_total += pf_ary[i].mhz;
		mhz_dbl_total += pf_ary[i].mhz_dbl;
	}
	printf("
Last mhz : %f(%u)
",mhz_dbl_total/32,(ULONGLONG)floor(mhz_dbl_total/32+0.5));
	return 0;
}