Fletcher32: Add incremental API

[bergzand]

Contribution description

This PR extends the current fletcher32 checksum with an incremental API mode. This way the bytes to be checksummed can be supplied via multiple successive calls and do not have to be provided in a single consecutive buffer.

I've also rephrased the warning with the original function a bit as that function uses an unaligned_get_u16 to access the data. The data thus does not require alignment, but the length does need to be supplied as number of 16 bit words.

Testing procedure

The test has been extended

Issues/PRs references

None

[Teufelchen1]

Only minor remarks by me and one static-test! 💪

[Teufelchen1]

🦐

[riot-ci]

Murdock results

✔️ PASSED

a00702e Fletcher32: Rephrase note on 16 bit word operations

Success	Failures	Total	Runtime
7937	0	7937	16m:00s

Artifacts

• Documentation preview

[kaspar030]

... waiting for users passing in byte array length as "words" ...

[bergzand]

... waiting for users passing in byte array length as "words" ...

The whole api of this module has in my opinion always been a huge footgun. Any suggestions here?

[kaspar030]

The whole api of this module has in my opinion always been a huge footgun. Any suggestions here?

Agreed. Now that there's a struct with state, buffer single bytes there if necessary?

[kaspar030]

... but of course I don't want to hold up the already ACK'ed PR.

[bergzand]

Agreed. Now that there's a struct with state, buffer single bytes there if necessary?

1. Follow up
2. How would you handle the case where the full length of the (incrementally passed) data is odd?

[benpicco]

Feel free to squash

[bergzand]

Squashed!

[benpicco]

bors merge

[bors]

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• Murdock
• static-tests
• tools-build-success