On core_cm4.h why is there casting like ((uint32_t)(int32_t)IRQn)?

Question

In the following code from core_cm4.h why is there a double cast ((uint32_t)(int32_t)IRQn)?

For example in the following function:

__STA         


        

Answer 1

Assuming IRQn is an integer (any signed integer type) in the range you say, then (uint32_t)(int32_t)IRQn is exactly the same as (uint32_t)IRQn.

The author of the code possibly didn't understand C type conversion rules; which are based on values, not representations. Converting -3, for example, to uint32_t always gives UINT32_MAX - 2 regardless of which data type the -3 was. It's the value of "negative 3" that matters.

(The other answer explains the difference between using a cast and no cast at all).