A method and structure for an in-place transformation of matrix data. For a matrix A stored in one of a standard full format or a packed format and a transformation T having a compact representation, blocking parameters MB and NB are chosen, based on a cache size. A sub-matrix A1 of A, A1 having size M1=m*MB by N1=n*NB, is worked on, and any of a residual remainder of A is saved in a buffer B. Sub-matrix A1 is worked on by contiguously moving and contiguously transforming A1 in-place into a New Data Structure (NDS), applying the transformation T in units of MB*NB contiguous double words to the NDS format of A1, thereby replacing A1 with the contents of T(A1), and moving and transforming NDS T(A1) to standard data format T(A1) with holes for the remainder of A in buffer B. The contents of buffer B is contiguously copied into the holes of A2, thereby providing in-place transformed matrix T(A).