Julien Rouhaud wrote:
> On 12/10/2016 14:32, Alvaro Herrera wrote:
> > Julien Rouhaud wrote:
> > 
> >> and you can instead make macaddr64 support both format, and provide a
> >> macaddr::macaddr64 cast
> > 
> > Having macaddr64 support both formats sounds nice, but how does it work?
> > Will we have to reserve one additional bit to select the representation?
> > That would make the type be 65 bits which is a clear loser IMO.
> > 
> > Is it allowed to just leave 16 bits as zeroes which would indicate that
> > the address is EUI48?  I wouldn't think so ...
> From what I read, you can indicate it's an EUI-48 address by storing
> FF:FF (or FF:FE for MAC-48) in 4th and 5th bytes of the EUI-64 address.

That seems reasonable at first glance; so the new type would be able to
store both 48-bit and 64-bit values, and there would be assignment casts
in both directions and a suite of operators to enable interoperability
of 48-bit values in macaddr8 with values in type macaddr.  Right?

(The cast function from macaddr8 to macaddr would raise error if the
4th and 5th bytes are not either FF:FF or FF:FE -- I don't think we can
in practice distinguish EUI-48 from MAC-48 in this context.  The cast in
the other direction would have no restriction and should probably always
use FF:FE).

Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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