[riot-notifications] [RIOT-OS/RIOT] dhcpv6_client: fix scaling of get_rand_us_factor (#16661)

Martine Lenders notifications at github.com
Tue Jul 20 19:54:49 CEST 2021


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### Contribution description
>From what I can tell, this is a bug. The [RFC defines RAND "a random number chosen with a uniform distribution between -0.1 and +0.1."](https://datatracker.ietf.org/doc/html/rfc8415#section-15), so we want to first take a number between 0μs and 200000μs and then subtract 100000μs from it to get the desired range, not take a number between 0μs and 200000μs and then subtract 100000000μs like it is the case in the current code.
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### Testing procedure
Since I found this bug only through code review, I'm not sure how to test this. I think the retransmission times of the DHCPv6 should now be far less erratic.
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### Issues/PRs references
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You can view, comment on, or merge this pull request online at:

  https://github.com/RIOT-OS/RIOT/pull/16661

-- Commit Summary --

  * dhcpv6_client: fix scaling of get_rand_us_factor

-- File Changes --

    M sys/net/application_layer/dhcpv6/client.c (2)

-- Patch Links --

https://github.com/RIOT-OS/RIOT/pull/16661.patch
https://github.com/RIOT-OS/RIOT/pull/16661.diff

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