Replace use of C11 atomics with atomic utils. This fixes
> error: address argument to atomic operation must be a pointer to a
> trivially-copyable type ('_Atomic(int) *' invalid)
error when compiling on AVR with LLVM.
This adds a simple macro to check (at C level) whether a given
expression is proven to be compile time constant and suitable for
constant folding. This allows writing code like this:
```C
int gpio_read(gpio_t pin) {
if (IS_CT_CONSTANT(pin)) {
/* this implementation should even be able to use the port and
* pin number as immediate in inline assembly */
}
else {
/* less efficient implementation that cannot use port and pin
* number as immediate in inline assembly */
}
}
```
This provides the same functionality as `static_assert()` provided by
C11 and has no advantages compared to it. Hence, encourage users to use
standard C functionality instead.
For the caller there should be no difference if there is no message
in the queue and if there can't be a message in the queue.
The current API works as one would expect if there is a message queue,
but once called from a thread that does not have a message queue
configured, code that does
while (msg_avail())
will end up in an infinite loop.
Remove this foot-gun from the API by making the return value of
msg_avail() independend of the availability of a message queue.
`WITHOUT_PEDANTIC(expr)` disables `-Wpedantic` for `expr`, but switches
back to the previous diagnostic settings afterwards. This helps defining
macros that are not strictly ISO compliant without having to drop the
`-Wpedantic` flag entirely.
`DECLARE_CONSTANT(identifier, const_expr)` declares an anonymous `enum`
constant named `identifier` and assigns it the value `const_expr`. Here,
`const_expr` has to be a compile time constant, but is not needed to be
an integer constant expression. It basically is a tool to magically
convert a non-integer constant expression into a integer constant
expression.
Calculate the size of the element based on the array given, not based
on the element pointer.
The element might as well be given as a `void *` via a callback.
In that case, if the user forgets to cast the `void *` to the array
element type, the calculation returns false values.
Disarm this foot gun by basing the element size off the given array.
