hello.
In general (or from your experience), is there difference in performance between for and while loops?
What if they are doubly/triply nested?
Is vectorization (SSE) affected by loop variant in g++ or Intel compilers?
Thank you
+8
A:
Any intelligent compiler won't really show a difference between them. A for loop is really just syntactic sugar for a certain form of while loop, anyways.
Amber
2010-05-21 02:01:27
+1
A:
it should be negligible. an optimizing compiler should make the distinction nonexistent.
sreservoir
2010-05-21 02:01:37
+1
A:
This is something easily ascertained by looking at disassembly. For most loops, they will be the same assuming you do the same work.
int i = 0;
while (i < 10)
++i;
is the same as
for (int i = 0; i < 10; ++i)
;
As for nesting, it really depends on how you configure it but same setups should yield same code.
dash-tom-bang
2010-05-21 02:04:02
+1
A:
Should be zero difference, but do check as I've seen really crappy, older versions of GCC create different code ARM/Thumb code between the two. One optimized away a compare after a subtract to set the zero flag where as the other did not. Was very lame.
Nesting again should make no difference. Not sure on SSE/Vectorization stuff, but again I'd expect there to be no difference.
Michael Dorgan
2010-05-21 02:05:55
this is excellent, thank you
aaa
2010-05-21 02:08:35
I think this paragraph sums it all up beautifully: "*Optimizing == important. But often: Readable code == more important.*"I tend to favour `for` loops for iteration as it is clear where your loop variable is being initialised and incremented or decremented.
Johnsyweb
2010-05-21 02:44:52