Rounding/create C function question

Hi,

I need some custom rounding function (say 1 or two decimal points),
what would be the simplest way to make one?

- Robert

P.S. I tried to create one in C like

#include <string.h>
#include "postgres.h"

double tst5(double x) {
return x; // ... whatever needed
}

and compiled it with (on RadHat 6.1, PG 6.5.3)

gcc -I/usr/include/pgsql -fPIC -shared
-o libeucto.so.0.0.2 -Wl,-soname,libeucto.so.0.0.2 eucto_round.c

CREATE FUNCTION tst5(float8) RETURNS float8
AS '/mnt/lotrando_c/projekty/eucto/bin/libeucto.so.0.0.2' LANGUAGE
'c';

This works as long as the function is int4/int4, but for float8 'backend
terminated abnormally'. Thanks for any help.