v3.1.0 volk_32fc_s32f_atan2_32f.h avx2 and avx2_fma kernels return NaN for an input element 0+0j

[jj1bdx]

Synopsis

VOLK v3.1.0 volk_32fc_s32f_atan2_32f() returns -nan for the following kernels when an input element is 0+0j:

• avx2 (a_avx2, u_avx2)
• avx2_fma (a_avx2_fma, u_avx2_fma)

VOLK v3.1.0 volk_32fc_s32f_atan2_32f() returns zero for the following kernels when an input element is 0+0j:

• generic
• polynomial

(where j^2 = -1)

Tested on Ubuntu 22.04.3 x86_64.

Test details are available at: https://gist.github.com/jj1bdx/62e27aac4b54a29dfafe210c73c49b0e

What should be done

The avx2 and avx2_fma kernels should behave the same as the generic and polynomial kernels, i.e., returning zero when the input is 0+0j. I have to screen this irregularity in my own application as in this example, which affects the overall performance and introduces unnecessary complexity.

I would appreciate it if the original author of the kernel would kindly help fix this bug.

References

• Issue new kernels for atan2 #636
• Speeding up atan2f by 50x
  • In the Edge Cases section of this article, the author explicitly states that: "All our functions do not handle inputs containing infinity, or when both x and y are 0, while conforming implementations must handle them specially". So, this is assumed to be a known issue.

[jdemel]

Thanks for this detailed bug report. I agree, all kernels should follow the generic behavior.