converting uid/gid to abstract credentials

[n0g0013 <ttw+bsd%cobbled.net@localhost>]

planning to begin tackling a variety of changes in the kernel.  the
first of which is to abstract and extend user credentials (initially
to remove the group membership limit).  however, initial engagement
with POSIX on the subject would seem to define 'uid_t' and 'gid_t' as
'integer types'.  however, 'integer type' does not appear to be defined
except within the loose terms of C99 (the best i can understand).

as such i'm looking for opinions and definite issues that may arise
from using an abstract encoding of 'uid_t' similar to BCD.

my main worry is that arithmetic operations may be implied from the
definition but my initial thoughts suggest to me that, whist it may
be an integer value, it is an identifier and not a number.  therefore
arithmetic operations are not of real concern.  i.e. we gain nothing
by adding, subtracting or dividing these identifiers only from testing
their equality.  in this sense any abstract encoding is irrelevant
as long as they are 'equal' when the 'the same' (if that makes any
sense).

i'm in the early stages of this design and so probably cannot fully
or easily explain all my ideas or intentions but your assistance in
understanding any possible pitfalls is appreciated.

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