On Thursday, 2 April 2015 at 05:21:08 UTC, thedeemon wrote:
std.algorithm.reverse uses ranges, and shamefully DMD is really bad at optimizing away range-induced costs.
The specialisation of reverse selected for slices does not use the range interface, it's all just indexing. The only overheads come from:
a) function calls, if the inliner isn't doing its job (which it really should be in these cases).
b) a check for aliasing in swapAt, which is only done for ranges of static arrays. Again, should be optimised away in this case, but it's possible DMD doesn't manage it. Either way, it's a trivially predictable branch and should be effectively free at the CPU level.
Once you've got past those, it's just straight loop I posted before.
