Issue with unsigned integer LOCAL_PREF

[Ondrej Zajicek]

On Wed, Nov 25, 2020 at 11:43:29AM +0100, Alexandre Corso wrote:
> Hello Bird team, 
>  
> Thank you for the great tool BIRD. I would like to open an issue (bird v2.0.7) about the local_pref.
>  
> ...
>  
> We had an exception to check the value of local_pref (on the filter)
> but can we have the something on the code, not to overflow the
> local_pref, for example SET to 0 if the value overflow?

Hello

There are at least three reasonable behaviors for fixed-range
arithmetics:

1) silent overflow (current behavior)

2) silent saturation (as you suggested)

3) explicit (logged) error

Not really sure which is better. (1) is likely least astonishment (for
fixed-range), (2) is most useful when overflows are intentional, (3) is
most useful when overflows are unintentional.

I have minor preference for (3), but no strong preference either way to
change anything. Also note that in cases when fixed-range attributes have
lower range than 32bits (i.e. 16bit preference and 24bit ospf_metrics),
we generate explicit error on overflow on assignment.

Or perhaps we should just move to arbitrary-range integers .. many new
RFCs already use 64bit attributes anyways.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."