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;
}