This is what I knew about it:
> `attribute((const))` function attribute
> Many functions examine only the arguments passed to them, and have no effects
except for the return value. This is a much stricter class than
`attribute((pure))`, because a function is not permitted to read global
memory. If a function is known to operate only on its arguments then it can be
subject to common sub-expression elimination and loop optimizations.
>https://stackoverflow.com/questions/29117836/attribute-const-vs-attribute-pure
-in-gnu-c