# Re: [eclipse-clp-users] Two problems with the ic-Solver

From: Joachim Schimpf <joachim.schimpf_at_...44...>
Date: Thu, 11 Feb 2010 12:44:33 +1100
```Andreas Berger wrote:
...
> I want to express a Constraint of the Form:
>
> "Give me a Number X, which is bitwise connected (C++ '&' ) with a second
> Number A is 0.
>
> Something like:  A /\ X = 0, give me a possible X when A = 9.
>
> I can't find an appropiate predicate for such kind of problem. I tried
> the following construct:
> 9 /\ X #= 0,  but of course it does not work.
>
> Can someone give me a hint to solve this problem please.

First, you should consider whether it is not better to use boolean (0/1)
variables for the individual bits.  Your constraints may then be easier
to express.  For example, if you represent your numbers as lists of
boolean digits, you can define

bool_bitand(X, Y, Z) :-
( foreach(Xi,X), foreach(Yi,Y), foreach(Zi,Z) do
[Xi,Yi,Zi]::0..1,
Zi #= (Xi and Yi)
).

?- bool_bitand(X, [1, 0, 0, 1], [0, 0, 0, 0]).
X = [0, _368{[0, 1]}, _457{[0, 1]}, 0]
Yes (0.00s cpu)

Second, if your bit vectors represent sets, you could also consider
using the ic_set solver's set-variables to represent them.

Third, with your original representation, you could prototype such
a constraint as follows:

:- lib(propia).

int_bitand(X, Y, Z) :- ( labeling([X,Y,Z]), X/\Y =:= Z ) infers ic.

which solves your example in this way:

?- X :: 0 .. 9, int_bitand(X, 9, 0).
X = X{[0, 2, 4, 6]}
Yes (0.00s cpu)

-- Joachim
```
Received on Thu Feb 11 2010 - 02:43:52 CET

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