Re: [musl] [PATCH] complex: fix comment in cacosh

[Rich Felker <dalias@libc.org>]

On Sun, Mar 10, 2024 at 09:00:40PM +0100, Szabolcs Nagy wrote:
> The principal experssions defining acosh and acos are such that
> 
>   acosh(z) = +-i acos(z)
> 
> where the + is only true on the Im(z)>0 half of the complex plane
> (and partly on Im(z)==0 depending on number representation).
> 
> fix the comment without expanding on the details.
> ---
>  src/complex/cacosh.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/complex/cacosh.c b/src/complex/cacosh.c
> index 76127f75..586328ce 100644
> --- a/src/complex/cacosh.c
> +++ b/src/complex/cacosh.c
> @@ -1,6 +1,6 @@
>  #include "complex_impl.h"
>  
> -/* acosh(z) = i acos(z) */
> +/* acosh(z) = +-i acos(z) */
>  
>  double complex cacosh(double complex z)
>  {

I'm fine with taking this patch as-is, but it naturally raises a
question: should it instead be:

-/* acosh(z) = i acos(z) */
+/* acosh(z) = ±i acos(z) */

IOW, should we use non-ascii characters in comments like this? My
leaning would be yes, especially since it may be needed to properly
attribute an algorithm or something where the only alternative is
misspelling someone's name or leaving it out entirely.

Really the only consideration for not doing this would be if it
actively breaks compiling in some environments, but I don't think
that's the case.

Rich