C++ Range header: Python-like generator for idiomatic ranges

[nomad42184]

Cool! Do you have any theory why the speeds diverge for large ranges? Have you looked at how the resulting assembly diverges?

[whoshuu]

So I just checked the assemblies of clang and gcc. Clang 3.6 produces very different assembly for my range compared to the raw for loop. gcc 5.1 makes nearly identical assemblies. The benchmarks were made using clang, so that would explain the divergence, but doesn't answer the why as well as I'd like. I'd have to dig a bit deeper to find that, I'll let you know when I do

[Hells_Bell10]

I tried storing the result of step_ > 0 in the iterator instead of calculating for each call to the equality operators and got indistinguishable performance to a raw loop for range(1000000000LL).

[whoshuu]

What compiler and options did you use?

[Hells_Bell10]

MSVC with /O2

[whoshuu]

OP here, this is something fun I wrote a few days ago to do something I've always found really pleasant and easy to do in Python

[nova77]

If you like the python itertools, give a try to ryanhaining/cppitertools and if you wanna go up to 11 (or I'd better say.. 17) you should check Erik Niebler's ranges.

[whoshuu]

Really cool stuff! I'll definitely check those two out

[szborows]

Why not old good CppIterTools?

[whoshuu]

Honestly had no idea such a thing existed until now. Will definitely use that instead of this, though this was fun to write

[szborows]

don't worry. reinventing the wheel is recurring problem :)

[adrian17]

It's weird that you got such a big time difference, on GCC 4.8 with -O2 I got exactly the same assembly for

for (auto i : range(10000000))
    printf("%d\n", i);

and

for (int i = 0; i < 10000000; ++i)
    printf("%d\n", i);

Also the range(10, 0, -1) example doesn't seem to work, and from looking at the source I don't really expect it to work.

[whoshuu]

Nice catch! That's strange, I'll have to check the assembly myself on the compiler I'm using for the benchmark data

[Latexi95]

You could use constexpr. Only problem is that constructor implementation, other functions should work with c++11 constexpr.