Extending a bit string

Currently the behavior of bit-string extensions is pretty insane.

SELECT b'01'::bit(2)::bit(4),
b'01'::bit(2)::int::bit(4);
bit | bit
------+------
0100 | 0001
(1 row)

I'd like propose we standardize this a bit. Previously, in version 8
compatibility was broke. From the Version 8 release notes (thanks to
Rhodium Toad for the research),

> Casting an integer to BIT(N) selects the rightmost N bits of the integer,
not the leftmost N bits as before.

Everything should select the right-most bits, and extend the left-most bits
from the docs:

> Casting an integer to a bit string width wider than the integer itself
will sign-extend on the left.

That makes sense to me. Intergers sign-extend on the left, and the behavior
is currently undefined for bit->bit extensions. What say you?

--
Evan Carroll - me(at)evancarroll(dot)com
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web: http://www.evancarroll.com
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