Luca Ferrari <fluca1978(at)gmail(dot)com> writes:
> I'm trying to define a custom data type that would represent a number
> of bytes in a lossy human way.
You did not show us the SQL definition of the type. I don't see anything
obviously wrong in what you showed (other than hfsize_add not setting the
result's scaling), so the problem is somewhere else. Given this C
declaration, the type probably needs to be size 16, double alignment,
pass-by-reference; maybe you messed up part of that?
> HFSize *sum = new_HFSize();
What is new_HFSize?
regards, tom lane