Is switch just as bad as if?

Question

I read on StackOverflow that using

if(someCondition)
{
    someCode();
}
else
{
    alternateCode();
}

can be inefficient due to susceptibility to branch misprediction (see this question for example).

So is a switch-construct, e.g.,

switch (someCondition)
{
    case (someCase):
        something();
        break;
    case (otherCase):
        someOtherInstructions();
        break;
    default:
        defaultAction();
        break;
}

any different in this respect (besides the fact that I have allowed for three possibilities)?

That's a very rare definition of 'expensive'! It's sort of like saying that $0.0001 is expensive. — Gabe, Jun 03 '13 at 06:30
@Gabe: as always, that depends on the application. IF you need to spend $0.0001 several billion times, it does start to matter (although I agree it hardly ever is the majority of the cost). — Rody Oldenhuis, Jun 03 '13 at 06:38
I prefer case statements because they're easier to read and reduces the chance of logic errors on the part of the programmer. No idea whether there's a difference in efficiency of the actual execution. — CaffeineConnoisseur, Jun 03 '13 at 06:46
Related (perhaps Java specific): http://stackoverflow.com/questions/2086529/what-is-the-relative-performance-difference-of-if-else-versus-switch-statement-i — Rody Oldenhuis, Jun 03 '13 at 06:49
Related (perhaps C++ specific): http://stackoverflow.com/questions/97987/advantage-of-switch-over-if-else-statement — Rody Oldenhuis, Jun 03 '13 at 06:50
Related (perhaps C# specific): http://stackoverflow.com/questions/445067/if-vs-switch-speed — Rody Oldenhuis, Jun 03 '13 at 06:51

score 4 · Accepted Answer · answered Jun 03 '13 at 11:16

4

if statements aren't "expensive", conditional branches may be. The issue isn't which of the many different high-level statements you choose to write - if, switch, for, while, etc. The issue is that modern computers work very well executing an unconditional instruction path, but when there's a decision point, they may slow down. Since you can't do anything interesting in computing without decision points (i.e., conditional branches), you might as well ignore the choice of high-level language construct.

answered Jun 03 '13 at 11:16

Ross Patterson

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Switch statements don't necessarily compile to conditional branches though (think jump tables). – sepp2k Jun 03 '13 at 11:28
1

I guess the main point here is, don't worry about it unless you are running a piece of code thousands (or millions) of times... – Mike Warren Jun 03 '13 at 18:13
@sepp2k Agreed. But that's a compiler decision and it can depend on the specific values involved. Regardless, the point isn't "if vs. switch", it's "conditional branch prediction". – Ross Patterson Jun 04 '13 at 03:40
long answer => http://stackoverflow.com/questions/315306/is-if-expensive – Louis Loudog Trottier Mar 12 '17 at 07:04

Is switch just as bad as if?

1 Answers1