Comment by captaincrunch

2 months ago

This is fast, READABLE, and accurate:

bool is_leap_year(uint32_t y) { // Works for Gregorian years in range [0, 65535] return ((!(y & 3)) && ((y % 25 != 0) || !(y & 15))); }

12 comments

captaincrunch

Reply

andrepd 2 months ago

This impl is mentioned in TFA.. It's much slower and includes branches.

hoten 2 months ago
I'd expect even without optimizations on, there wouldn't be branches in the output for that code.
- kragen 2 months ago
  
  There are, even with optimizations on. You could have checked: https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename...
  I didn't find any way to get a compiler to generate a branchless version. I tried clang and GCC, both for amd64, with -O0, -O5, -Os, and for clang, -Oz.
  
  4 replies →

windward 2 months ago

>READABLE

Great. It will be useful for the exhaustive tests of the faster version.

kragen 2 months ago

You commented out your entire function body and the closing }. Also, on 32-bit platforms, it doesn't stop working at 65535.

captaincrunch 2 months ago
just a formatting issue on my side, there were \n.
- archargelod 2 months ago
  
  This website eats newlines, unless you double them (one of the annoying features of markdown). You can use codeblocks by putting 4 spaces before each line:
  int main() { // this should be properly formatted return 0; };
- kragen 2 months ago
  
  If you fix it, other people can test your code without having to fix the syntax themselves first.