Unrolling loops by hand was a typical source-code optimization technique before compilers were available that could perform this restructuring automatically. A loop written as:
DO K = 1, N-5, 6 DO J = 1, N DO I = 1,N A(I,J) = A(I,J) + B(I,K ) * C(K ,J) * + B(I,K+1) * C(K+1,J) * + B(I,K+2) * C(K+2,J) * + B(I,K+3) * C(K+3,J) * + B(I,K+4) * C(K+4,J) * + B(I,K+5) * C(K+5,J) END DO END DO END DO DO KK = K,N DO J =1,N DO I =1,N A(I,J) = A(I,J) + B(I,KK) * C(KK,J) END DO END DO END DO |
should be rewritten the way it was originally intended:
DO K = 1,N DO J = 1,N DO I = 1,N A(I,J) = A(I,J) + B(I,K) * C(K,J) END DO END DO END DO |