Stsck mem optimization for sha256 hash generation

[toshiharutf]

Made buffers in mavlink_sha256_calc thread_local to save space in stack.

[peterbarker]

This PR is against a repository which contains generated commits; it should be against the generator instead.

One issue with that patch is that I don't believe we currently have a C11 prerequisite for compilation - and this would introduce that.

[toshiharutf]

Hello Patrick,
thanks for your time to review my PR. It's my first developing for mavlink. Is mavlink generator a github pipeline? is that related to https://hamishwillee.gitbooks.io/ham_mavdevguide/content/en/ ? Where should I create the PR then?

Also, according to this doc https://mavlink.io/en/guide/mavlink_2.html, mavlink2 should be C++11 compliant. I could use static, instead of thread_local, but it would only be safe to use for single threaded applications.

Bests,

[hamishwillee]

@peterbarker The generator separately supports generation of Cpp11 libraries from the normal C library in this repo. So in theory we'd accept a generator fix that made that version more compliant. But as you say, not this one.

@toshiharutf Firstly, thanks for contributing :-). I presume you are using this library in anger?

Also, according to this doc https://mavlink.io/en/guide/mavlink_2.html, mavlink2 should be C++11 compliant. I could use static, instead of thread_local, but it would only be safe to use for single threaded applications.

No, according to that statement MAVLink supports C++11 compliant libraries. That's true, but it isn't this library. This library is generated using --lang=c (for generator docs ).

What @peterbarker is saying is that this library is generated from source files somewhere else. So you need to update the originals or the change would be swamped next time we update the library. The original file, where a PR would be required is of this change is : https://github.com/ArduPilot/pymavlink/blob/master/generator/C/include_v2.0/mavlink_sha256.h

In summary, you would need to run the generator and see what is generated. If it is the file https://github.com/ArduPilot/pymavlink/blob/master/generator/C/include_v2.0/mavlink_sha256.h then that would mean it is shared by both builds - so you'd have to either conditionally build your changes or split the file.

I'm going to close this as invalid.