[HACKERS] index a datatype

[Ewald Geschwinde]

I have looked at the cube datataype in the contrib but I''m not sure 
that I'm on the right way

I have found these functions:

-- support routines for indexing

CREATE FUNCTION cube_union(cube, cube) RETURNS cube
        AS 'MODULE_PATHNAME' LANGUAGE 'c' with (isstrict);

CREATE FUNCTION cube_inter(cube, cube) RETURNS cube
        AS 'MODULE_PATHNAME' LANGUAGE 'c' with (isstrict);

CREATE FUNCTION cube_size(cube) RETURNS float4
        AS 'MODULE_PATHNAME' LANGUAGE 'c' with (isstrict);


and there are the same functions written in c in the file

/* cube_union */
NDBOX *
cube_union(NDBOX * box_a, NDBOX * box_b)
{
        int                        i;
        NDBOX           *result;
        NDBOX           *a = swap_corners(box_a);
        NDBOX           *b = swap_corners(box_b);

        if (a->dim >= b->dim)
        {
                result = palloc(a->size);
                result->size = a->size;
                result->dim = a->dim;
        }
        else
        {
                result = palloc(b->size);
                result->size = b->size;
                result->dim = b->dim;
        }

        /* swap the box pointers if needed */
        if (a->dim < b->dim)
        {
                NDBOX           *tmp = b;

                b = a;
                a = tmp;
        }

        /*
         * use the potentially smaller of the two boxes (b) to fill in the
         * result, padding absent dimensions with zeroes
         */
        for (i = 0; i < b->dim; i++)
        {
                result->x[i] = b->x[i];
                result->x[i + a->dim] = b->x[i + b->dim];
        }
        for (i = b->dim; i < a->dim; i++)
        {
                result->x[i] = 0;
                result->x[i + a->dim] = 0;
        }

        /* compute the union */
        for (i = 0; i < a->dim; i++)
                result->x[i] = min(a->x[i], result->x[i]);
        for (i = a->dim; i < a->dim * 2; i++)
                result->x[i] = max(a->x[i], result->x[i]);

        pfree(a);
        pfree(b);

        return (result);
}


Now my question is:

Is it easy to write an indexed datatype without touching the, let's say 
internal code, of postgresql
Are there some problems when writing indexed datatypes?

Any information and suggestaions welcome

Ewald





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