> On 10 Jul 2015, at 11:37, David Ham <David.Ham@imperial.ac.uk> wrote:
>
>
> That's quite yuck, however I can see the attraction as we're kind of sort of not mucking with the PyOP2 interface.
>
> However the generated code is specific to BCs applied to a particular component, which doesn't satisfy Justin's (very standard) use case.
>
> I think we need to encode *which* component we're changing into the map value. EG.
>
> val = -val -(2**(30-i))
>
> where i is the component. This can be decoded to zero the correct entry in a general purpose way. The downside is that we limit ourselves to about half a billion nodes per core. I think that's OK.
OK, so it may be that a node may have more than one component zeroed (e.g. at a corner).
So how about this:
Reserve top 2 (3?) bits to encode the component:
x = sum(2**idx for idx in indices)
val = val + (x << 29)
Convert to negative
val = -(val + 1)
In the generated code we can then unwind that and pull out the appropriate components.
This could work. They're all pretty ugly solutions, tbf.
Lawrence