Question

Bit of a weird one: I was told a while ago by a friend that rearranging this example for loop from :

for(int i = 0; i < constant; ++i) {     // code... } 

to:

for(int i = 0; constant > i; ++i) {     // code... } 

would slightly increase performance in C++. I don’t see how comparing a constant value to a variable is faster than vice-versa, and some rudimentary tests I ran didn’t show any difference in speed between the two implementations. The same was also true of testing this Python while loop:

while i < constant:     # code...     i += 1 

vs:

while constant > i:     # code...     i += 1 

Am I wrong? Are my simple tests not enough to determine the speed variation? Is this true of other languages? Or is this just a new best practice?

Answer 1

It’s more in the line of C++ folklore, hand micro-optimizations that worked once on a particular version of a particular compiler and get passed down ever after as some kind of lore distinguishing the possessor from the common herd. It’s rubbish. Profiling is truth.