Skew

A skew() method is a communication schedule for performing a skewed shift--a shift where the shift amount is itself an array--in a particular dimension of a distributed array placing the result in another array. The source and destination must have the same shape and same element-type, and they must be identically aligned. The skew() operation does not copy values from source array that would go past the edge of destination array, and at the other extreme of the range elements of destination that are not targeted by elements from source array are unchanged from their input value. The related operation cskew() is almost identical to skew() except that it implements a circular shift, rather then an ``edge-off'' shift. General signature of skew() function is

where the variable $T$ runs over all primitive types and Object, and the notation $T$ # means a multiarray of arbitrary rank, with elements of type $T$. The shift argument is a multiarray. The elements of this array specifies the amount and direction of the shift. The shift-amount array should have rank one less than the source array. The dimension argument is in the range 0, ...,$R$-1 where $R$ is the rank of the arrays. The skew method is implemented by a schedule object with HPspmd class Skew$T$. Each primitive type and Object has its own schedule class. This class has a constructor with arguments identical to the method above, and has one public method with no arguments called execute(), which executes the schedule. The effective public interface of the Skew$T$ class is

$$\begin{minipage}[t]{\linewidth}\small\verb$ public class Shift$$T... ...ublic void execute () { ... }$\\ \verb$ . . .$\\ \verb$ }$ \end{minipage}$$

The source array is the source and the destination array is destination. The array of shift mounts is shift The dimension argument selects the array dimension in which the shift occurs. The flag mode specifies the type of shift. It takes one of the values Adlib.CYCL, Adlib.EDGE, or Adlib.NONE.