[a_e_k]

It doesn't need to be that complicated at all. The book "Hacker's Delight" gives some nice, fairly simple implementations. Here's one:

http://www.hackersdelight.org/hdcodetxt/hilbert/lams.c.txt

[vanderZwan]

H-curves are not Hilbert curves! I know, the name is very confusing, but read the PDF: H-curves have better locality than Hilbert curves (possibly even optimal).

And I'm sure that constructing H-curves doesn't need to be as complicated as that linked academic code makes it look, but for now I don't know of any implementation.

Thanks for the link though :)