non-overlapping ranges constraint?

Suppose I have a table

CREATE TABLE range (min int NOT NULL, max int NOT NULL, otherdata TEXT);

I want to make sure that no two tuples in this table describe
overlapping ranges, that is:

tuple1.min<=tuple2.max AND tuple1.max>=tuple2.min

I arrived at doing the checking using a custom function:

CREATE FUNCTION range_available(int, int) RETURNS bool AS
'LOCK TABLE range;
SELECT count(*)=0 FROM range WHERE min<= $2 AND max>= $1
AND min != $1 AND max != $2;
' LANGUAGE 'sql';

ALTER TABLE range ADD CONSTRAINT check_range
CHECK (range_available(min, max));

This solves the probelm at hand but I have severe performance
problems. Inserts/deletes on the table are rare, as are modifications
to min and max, but the table is subject to mass-updates touching
otherdata and it appears that the check constraint is executed even
if neither min nor max are modified. Basically this turns updating
into an O(n^2) operation, as neither min<= $2 nor max >= $1
are particularly selective.

My question is whether there is a more elegant solution; since the
problem is essentially a geometric one, perhaps people storing
geometric objects know a generic solution? Additional fact:
in the "real" problem both min and max are of type timestamp.

Best regards
--
Helge Bahmann <bahmann(at)math(dot)tu-freiberg(dot)de> /| \__
Network admin, systems programmer /_|____\
_/\ | __)
$ ./configure \\ \|__/__|
checking whether build environment is sane... yes \\/___/ |
checking for AIX... no (we already did this) |