i < x or i != x?

Which would be the best/fastest way for evaluating the loop condition,

Code:

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while (i < x)

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or

Code:

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while (i != x)

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? Assuming that the loop is incrementing i for each iteration, to avoid elitist remarks :(

Well assuming you know that i will at some point be exactly x, then there is no difference. But consider any possibility that might result in i never equaling x. Such as this:

Code:

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float i = 0.0;
while (i != 1.0) {
  printf("%.2f\n", i);
  i += .1;
}

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Yes, the value of i will be the same as x's at some point, they are both integers and i is incrementing by one at a time.

Quote:

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Originally Posted by OnionKnight

Which would be the best/fastest way for evaluating the loop condition,

Code:

---

while (i < x)

---

or

Code:

---

while (i != x)

---

? Assuming that the loop is incrementing i for each iteration, to avoid elitist remarks :(

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I'm not an assembly expert, but I know on at least one architecture (ARM) those will both take exactly the same amount of time; cmp and then beq or bge (or bne vs blt); half a dozen in one hand and 6 in the other.

But even if some architectures have one compare go faster than the other, don't give it any thought. Micro-optimization is bad. Forget "fastest" and just concentrate on "best" - whatever makes sense, is easy to understand and maintain. Always go good coding style.

Yes I usually leave stuff like that up to the compiler but I figured that != would be the same as ! and ==, two operations whereas < would be just one but it seems like they actually do the same amount of work.
I've come to the conclusion that I'll use != in loops where the value will become the other at some point and < otherwise.

just for fun:

Code:

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int
main(void)
{
        unsigned i, start, stop, first, second, max = UINT_MAX;
        i = 0;
        start = clock();
        while(i < max) i++;
        stop = clock();
        first = stop - start;
        i = 0;
        start = clock();
        while(i != max) i++;
        stop = clock();
        second = stop - start;
        cout << "(i < max): " << first << endl;
        cout << "(i != max): " << second << endl;
}

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the first one seems to execute *slightly* faster than the second on my system, but it's negligible. I'd say follow moi's advice. :)