3 ms·

(I'm the author) You're right, I should have specified -- it is glibc 2.32-48 . This the source specifying how glibc is built: https://github.com/NixOS/nixpkgs

(I'm the author) You're right, I should have specified -- it is glibc 2.32-48 . This the source specifying how glibc is built: https://github.com/NixOS/nixpkgs/blob/97c5d0cbe76901da0135b05cdbdfc5b068a7942c/pkgs/development/libraries/glibc/default.nix https://github.com/NixOS/nixpkgs/blob/97c5d0cbe76901da0135b0... . I've amended the article so that it says `glibc` rather than `libc`, and added a sidenote specifying the version. I link to it statically as indicated in the gist, although I believe that shouldn't matter. Also see https://gist.github.com/bitonic/d0f5a0a44e37d4f0be03d34d47acb6cf#gistcomment-3864005 https://gist.github.com/bitonic/d0f5a0a44e37d4f0be03d34d47ac... . Note that the hardware is not particularly recent (Q3 2017), but we tend to rent servers which are not exactly on the bleeding edge, so that was my platform.

stephencanon 5y ago
Thanks for clarifying! Without benchmarking, I would expect atan2f to be around 20-30 cycles per element or less with either Intel's or Apple's scalar math library, and proportionally faster for their vector libs.
- rostayob 5y ago
  Thanks for the info. By the way, your writing on floating point arithmetic is very informative -- I even cite a message of yours on FMA in the post itself!
floxy 5y ago
Thanks for the interesting writeup. I wonder if it is because glibc has a less-optimized atan2f (for floats). The double version seems quite involved in glibc anyway: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/dbl-64/e_atan2.c;h=b77ad2dc6b9561e6396a76db11f6db686f170bb1;hb=ae37d06c7d127817ba43850f0f898b793d42aea7 https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/iee... ...where the atan2f version ends up calling atan, which doesn't seem as sophisticated: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/flt-32/s_atanf.c;h=f61b0f5ef64866fb053a87f9c1a968165ba4de2a;hb=ae37d06c7d127817ba43850f0f898b793d42aea7 https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/iee...

stephencanon 5y ago

Thanks for clarifying! Without benchmarking, I would expect atan2f to be around 20-30 cycles per element or less with either Intel's or Apple's scalar math library, and proportionally faster for their vector libs.

rostayob 5y ago
Thanks for the info. By the way, your writing on floating point arithmetic is very informative -- I even cite a message of yours on FMA in the post itself!

floxy 5y ago

Thanks for the interesting writeup. I wonder if it is because glibc has a less-optimized atan2f (for floats). The double version seems quite involved in glibc anyway: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/dbl-64/e_atan2.c;h=b77ad2dc6b9561e6396a76db11f6db686f170bb1;hb=ae37d06c7d127817ba43850f0f898b793d42aea7 https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/iee... ...where the atan2f version ends up calling atan, which doesn't seem as sophisticated: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/ieee754/flt-32/s_atanf.c;h=f61b0f5ef64866fb053a87f9c1a968165ba4de2a;hb=ae37d06c7d127817ba43850f0f898b793d42aea7 https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/iee...