Yarp: os/Stamp should be using a fixed size type for counter

[drdanz]

The yarp::os::Stamp class uses int to represent the counter.
Since int has a different representation depending on the system, it should be using a fixed size type, for example int32_t.

Also it should probably use an unsigned type, i.e. uint32_t

[drdanz]

cc @Nicogene @traversaro

[pattacini]

@drdanz there are conditions where a negative counter (specifically -1) is employed to mean "invalid" or "not-available".

Ok for int32_t 👍🏻

[Nicogene]

@drdanz there are conditions where a negative counter (specifically -1) is employed to mean "invalid" or "not-available".

Exactly, if the Stamp is not defined it has -1 has seq number and 0.0 has ts, changing it would be a break of ABI

Ok for int32_t

[drdanz]

Technically, if only -1 is used, it could be possible to use uint32_t and define

getMaxCount() == std::numeric_limits<uint32_t>::max() - 1;

since -1 has the exact representation as std::numeric_limits<uint32_t>

(btw getMaxCount should be constexpr)

[pattacini]

since -1 has the exact representation as std::numeric_limits

Yeah, but then how this relates to checks like this below:

https://github.com/robotology/yarp/blob/71097ed9b24369d2709dc37298120130cc5c4868/src/libYARP_os/src/yarp/os/Stamp.cpp#L41-L44

If sequenceNumber is unsigned (likely it'll be changed to unsigned), then we need to change the check.
I'm afraid that similar checks might be spread around.