[riot-notifications] [RIOT-OS/RIOT] Pr random sha1prng optimize (#14053)

Peter Kietzmann notifications at github.com
Mon May 11 10:52:47 CEST 2020

### Contribution description

This PR optimizes the SHA1PRNG in three ways:
- Rename `SEED_SIZE` macro to `STATE_SIZE` to be more precise. Furthermore, initialize its value with the digest length given by SHA1 (`SHA1_DIGEST_LENGTH`). 
 - Use `random_init_by_array` in `random_init`.
-  Get rid of the redundant [SHA-1 update](https://github.com/RIOT-OS/RIOT/blob/master/sys/random/sha1prng.c#L65) during state transition.  The SHA-1 context is [reset during the next cycle](https://github.com/RIOT-OS/RIOT/blob/master/sys/random/sha1prng.c#L95) anyway.

### Testing procedure

- Run *tests/rng* with and without this PR.
- Dump a couple of numbers (`dump 100`) and compare both results.
-> Should be the same.
- On a board, run `speed`.
-> Should be slightly faster now.

### Issues/PRs references

You can view, comment on, or merge this pull request online at:


-- Commit Summary --

  * sys/random/sha1prng: rename seed size to state size
  * sys/random/sha1prng: remove redundant sha1 update in state transistion
  * sys/random/sha1prng: make random_init use init_by_array

-- File Changes --

    M sys/random/sha1prng.c (33)

-- Patch Links --


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