inet Operator Does not exists

Hello Team,

I am facing an issue with inet .

Locally i am using postgresql 8.3 and for remote server i am using 8.1

CREATE FUNCTION inet_to_bigint(inet) RETURNS bigint AS $$
SELECT $1 - inet '0.0.0.0'
$$ LANGUAGE SQL;

Now above querry works fine for 8.3 but not for 8.1. I was wondering if
there is some thing wrong from my side.

Below is the error message

ERROR: operator does not exist: inet - inet
HINT: No operator matches the given name and argument type(s). You
may need to add explicit type casts.
CONTEXT: SQL function "inet_to_bigint"

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Best Regards
Shakeel Abbas