原创:https://blog.csdn.net/ndzjx/article/details/84404268
1:本质:每次循环的CPU比例问题。
CPU调度时间片,大约为20ms
2.2GHz是CPU时钟周期,= 22亿次 = 2.2*10^9
每个时钟周期平均执行2条汇编指令
#include <stdio.h>
#include <windows.h>
#include <time.h>
#include <math.h>
int main()
{
///////////////////////////////
// // 2.2GHz * 10^9 * 2 / 5 每秒、减两个数量级
// for (; ;)
// {
// for(int i = 0; i < 8800000; i++)
// {
// }
// Sleep(10);// 接近Windows调度时间片
// }
// ///////////////////////////////////
// const DWORD busyTime = 20;
// const DWORD idleTime = busyTime;
// while(true)
// {
// // busy loop
// DWORD startTime = GetTickCount();
// while (GetTickCount() - startTime <= busyTime)
// {
// ;
// }
// // idle loop
// Sleep(idleTime);
// }
///////////////////////////////
const int SAMPLING_COUNT = 200;
const double PI = 3.1415926535;
const int TOTAL_AMPLITUDE = 300;
DWORD busySpan[SAMPLING_COUNT];
int amplitude = TOTAL_AMPLITUDE / 2;
double radian = 0.0;
double radianIncrement = 2.0 / (double)SAMPLING_COUNT;
for (int i = 0; i < SAMPLING_COUNT; i++)
{
busySpan[i] = (DWORD)(amplitude + sin(PI * radian) * amplitude);
radian += radianIncrement;
printf("sin(%f)\t%f\t%d\t%d\n", PI * radian, sin(PI * radian), busySpan[i], TOTAL_AMPLITUDE - busySpan[i]);
}
DWORD startTime = 0;
for (int j = 0;; j = (j + 1) % SAMPLING_COUNT)
{
startTime = GetTickCount();
while(GetTickCount() - startTime <= busySpan[j])
;
Sleep(TOTAL_AMPLITUDE - busySpan[j]);
}
return 0;
}