Effect:

If msk was non-null, the effect is like executing the conditional assignment

  if(msk [$x_0, \ldots, x_{S - 1}$]) 

    dst [$\mbox{\tt subs}_0$ [$x_0, \ldots, x_{S - 1}$], ...,              $\mbox{\tt subs}_{R - 1}$ [$x_0, \ldots, x_{S - 1}$]] = 

                         src [$x_0, \ldots, x_{S - 1}$]

for every tuple $(x_0, \ldots, x_{S - 1})$ of global subscripts of the source array. These assignments are executed in an undefined order. If msk is a null pointer, the assignment is unconditional. Here $\mbox{\tt subs}_r$ denotest the $r$th subscript array.