c – 纳秒到毫秒 – 快速划分1000000

明显的做法是除以1000000.
不过,我经常这样做,想知道是否会成为瓶颈.

处理像1000000这样的数字时,是否有优化的分割操作？

注意：任何代码必须可移植.我使用gcc,这通常是在Sparc硬件上

一些使用以下代码的快速测试…希望是对的.

#include <sys/time.h>
#include <iostream>

using namespace std;

const double NANOSECONDS_TO_MILLISECONDS = 1.0 / 1000000.0;

int main()
{
    hrtime_t start;
    hrtime_t tmp;
    hrtime_t fin;

    start = gethrtime();
    tmp = (hrtime_t)(start * NANOSECONDS_TO_MILLISECONDS);
    fin = gethrtime();

    cout << "Method 1"
    cout << "Original val: " << start << endl;
    cout << "Computed: " << tmp << endl;
    cout << "Time:" << fin - start << endl;

    start = gethrtime();
    tmp = (start / 1000000);
    fin = gethrtime();

    cout "Method 2"    
    cout << "Original val: " << start << endl;
    cout << "Computed: " << tmp << endl;
    cout << "Time:" << fin - start << endl;

    return 0;
}

示例输出：

Original val: 3048161553965997
Computed: 3048161553
Time:82082
Original val: 3048161556359586
Computed: 3048161556
Time:31230

Original val: 3048239663018915
Computed: 3048239663
Time:79381
Original val: 3048239665393873
Computed: 3048239665
Time:31321

Original val: 3048249874282285
Computed: 3048249874
Time:81812
Original val: 3048249876664084
Computed: 3048249876
Time:34830

如果这是正确的,那么在这种情况下,乘以倒数实际上更慢.这可能是由于使用浮点数学而不是固定点数学.我只会坚持整数除法,根本不需要任何时间.