If statement inside loop

[Shivam Malhotra]

Is it possible to put an if condition inside a loop to be parallelized.
My code looks like:

#define get_xp(a1,a2) xp[a1][a2]
#define get_R(a1) R[a1]   

   for(i=Nboun+1;i<=Npartstot;i++)
       {
           for (n=1;n<=3;++n)
           {
            j=neb[i][n];
            dxij[1]=xp[i][1]-get_xp(j,1);
            Rj =  get_R(j);
            temp1 = dxij[1];
            temp2 = L-rng*(R[i]+ Rj);
           
            if( temp1 > temp2){
                dxij[1]=dxij[1]-L;
              }
      
          }
      }


If need to read from nth neighbor of ith particle, so I use the #define trick suggested in earlier post.
Basically doing this is giving me the following error at the if condition : "variable or array reference in an affine expression".

The same if condition if I code as a ternary operator, it works fine with clan

dxij[1] = (temp1>temp2)? dxij[1] : dxij[1] - L


But my actual code should contain a number of instructions inside the if statement, thus I cannot make it all as ternary operator. Is there any workaround for this so that I can get through clan to feed it into pluto for parallelization?
I think I am not able to understand what is allowed in condition of if statement.

Sincerely,
Shivam Malhotra

[Cédric Bastoul]

Hi Shivam Malhotra,

I must admit Clan does not support this directly yet, except by using workarouds such as #define pragmas or ternary operators. The problem is, Clan only accepts at the moment non-data-dependent affine constraints in either conditions or loop bounds. The constraints are summarized there :

http://icps.u-strasbg.fr/~bastoul/development/clan/docs/clan_reference_card.pdf

Note that this is "just" a technical limitation : it is easy to extend this but we need some engineering time. It will be suported at some point, but it depends on the contributor time so I have no clear date when it will be available (if you want to contribute, I can explain your how ;-) !).

Best,

Cedric

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