When should pure function modify parameters?

[Guillaume Piolat]

On Wednesday, 19 November 2025 at 13:05:52 UTC, user1234 wrote:
>
> Isn't that because of the side effect on error ?
>
> (https://www.felixcloutier.com/x86/fpatan#fpu-flags-affected)

Probably because it sets errno, just like malloc and free.
And what is the popularity of pureMalloc / pureFree and would-be 
pureAtan2f ? Not very popular.