1. A method, comprising: performing, by a processor: receiving a selection vector, a basis vector, and a control vector; selecting a basis value from the basis vector dependent upon the selection vector; and generating a result vector dependent upon the basis value; wherein each of the selection vector, the basis vector, the control vector, and the result vector includes a respective plurality of elements that occupy N ordered element positions; wherein for each of the N ordered element positions, said generating comprises performing a fixed-value addition operation dependent upon the control vector and the basis value; wherein selecting the basis value from the basis vector selects the basis value from the basis vector at an element position in the basis vector that corresponds to a first active element of the ordered element positions in the selection vector; and wherein selecting the basis value further comprises selecting the basis value from a last ordered element position of the basis vector in response to a determination that a first ordered element position of the selection vector is active.