Question

我想比较两种不同的奇数或偶数测试方法，我想测试哪个更快，所以我尝试使用clock()函数和clock_t变量。

似乎没什么用。我在网上搜索了很多，并根据我在stackoverflow上找到的答案修改了我的代码，但仍然没有。

这是我的代码：

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<stdint.h>
clock_t startm, stopm;
#define START if ( (startm = clock()) == -1) {printf("Error calling clock");exit(1);}
#define STOP if ( (stopm = clock()) == -1) {printf("Error calling clock");exit(1);}
#define PRINTTIME printf( "%ju ticks used by the processor.", (uintmax_t)(stopm-startm));
#define COUNT 18446744073709551600
#define STEP COUNT/100

int timetest(void){
    unsigned long long int i = 0, y =0 , x = 76546546545541; // x  = a random big odd number
    clock_t startTime,stopTime;
    printf("\nstarting bitwise method :\n");
    START;
    for(i = 0 ; i < COUNT ; i++){
        if(x&1) y=1;
    }
    STOP;
    printf("\n");
    PRINTTIME;

    y=0;
    printf("\nstarting mul-div method :\n");
    START;  
    for(i = 0; i < COUNT ; i++){     
        if(((x/2)*2) != x ) y=1;
    }
    STOP;
    printf("\n");
    PRINTTIME;
    printf("\n\n");
    return 0;
}

我总是以0 ticks used by the processor.作为输出。

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修改：

iv有足够的编译器问题。创建了上述程序的java版本。给了我答案。虽然它适用于java平台。

public class test {
    private final static int count = 500000000;
    private final static long num = 55465465465465L;
    private final static int loops = 25;
    private long runTime;
    private long result;
    private long bitArr[] = new long[loops];
    private long mulDivArr[] = new long[loops];
    private double meanVal;

    private void bitwiser() {
        for (int i = 0; i < count; i++) {
            result = num & 1;
        }
    }

    private void muldiv() {
        for (int i = 0; i < count; i++) {
            result = (num / 2) * 2;
        }
    }

    public test() {
        // run loops and gather info
        for (int i = 0; i < loops; i++) {
            runTime = System.currentTimeMillis();
            bitwiser();
            runTime = System.currentTimeMillis() - runTime;
            bitArr[i] = runTime;
            runTime = System.currentTimeMillis();
            muldiv();
            runTime = System.currentTimeMillis() - runTime;
            mulDivArr[i] = runTime;
        }
        // calculate stats
        meanVal = stats.mean(bitArr);
        System.out.println("bitwise time : " + meanVal);
        meanVal = stats.mean(mulDivArr);
        System.out.println("muldiv time : " + meanVal);

    }

    public static void main(String[] args) {
        new test();
    }
}

final class stats {
    private stats() {
        // empty
    }

    public static double mean(long[] a) {
        if (a.length == 0)
            return Double.NaN;
        long sum = sum(a);
        return (double) sum / a.length;
    }

    public static long sum(long[] a) {
        long sum = 0L;
        for (int i = 0; i < a.length; i++) {
            sum += a[i];
        }
        return sum;
    }

}

输出（以毫秒为单位）：

bitwise time : 1109.52
muldiv time : 1108.16

平均来说，按位似乎比muldiv慢一点。

Answer 1

此：

#define COUNT 18446744073709551600

会溢出，您必须附加ULL才能使文字具有unsigned long long类型。

printf始终显示0个处理器时间作为输出

1 个答案: