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Could (x == 0) be more efficient than (0 == x)?

Possible duplicate:
Which one will run faster if (flag == 0) or if (0 == flag)?

Usually I write my terms of equality:

if(0==x)

as many people do, instead

if(x==0)

for the compiler to tell me when I accidentally typed = instead of ==.

Someone told me that some compilers implement this as two register loads, rather than a single operation with zero, and therefore it is less efficient.

Does anyone know if this is a reasonable comment?

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5 answers

Someone told me that some compilers implement this as two register loads, rather than using a zero operation

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+4

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if(conditionA && conditionB && (conditionC || conditionD)) {...}

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#include <stdio.h>
#include <stdlib.h>

    int main(int argc, char *argv[]) {
        int x = atoi(argv[1]);
        int zeros=0;
        int i;
        for (i=0; i<100000; i++) {
            if (0==x) {
                zeros++;
            }
        }
        printf("zeros: %d\n",zeros);
        return 0;
    }
0

Why not try 2 solutions?

#include <stdio.h>
#include <time.h>

#define LOOPS   1000000000

void main(void)
{
    clock_t start1, start2, end1, end2;
    int x=1,i;

    start1=clock();
    for(i=0;i<LOOPS;i++)
    {
        if (x==0)
        {
            x=1;
        }
    }
    end1=clock();

    start2=clock();
    for(i=0;i<LOOPS;i++)
    {
        if (0==x)
        {
            x=1;
        }
    }
    end2=clock();

    printf("x==0 %d ns\n", end1-start1);
    printf("0==x %d ns\n", end2-start2);
}
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