SUBROUTINE DSWAP(N,DX,INCX,DY,INCY) * .. Scalar Arguments .. INTEGER INCX,INCY,N * .. * .. Array Arguments .. DOUBLE PRECISION DX(*),DY(*) * .. * * Purpose * ======= * * interchanges two vectors. * uses unrolled loops for increments equal one. * * Further Details * =============== * * jack dongarra, linpack, 3/11/78. * modified 12/3/93, array(1) declarations changed to array(*) * * ===================================================================== * * .. Local Scalars .. DOUBLE PRECISION DTEMP INTEGER I,IX,IY,M,MP1 * .. * .. Intrinsic Functions .. INTRINSIC MOD * .. IF (N.LE.0) RETURN IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20 * * code for unequal increments or equal increments not equal * to 1 * IX = 1 IY = 1 IF (INCX.LT.0) IX = (-N+1)*INCX + 1 IF (INCY.LT.0) IY = (-N+1)*INCY + 1 DO 10 I = 1,N DTEMP = DX(IX) DX(IX) = DY(IY) DY(IY) = DTEMP IX = IX + INCX IY = IY + INCY 10 CONTINUE RETURN * * code for both increments equal to 1 * * * clean-up loop * 20 M = MOD(N,3) IF (M.EQ.0) GO TO 40 DO 30 I = 1,M DTEMP = DX(I) DX(I) = DY(I) DY(I) = DTEMP 30 CONTINUE IF (N.LT.3) RETURN 40 MP1 = M + 1 DO 50 I = MP1,N,3 DTEMP = DX(I) DX(I) = DY(I) DY(I) = DTEMP DTEMP = DX(I+1) DX(I+1) = DY(I+1) DY(I+1) = DTEMP DTEMP = DX(I+2) DX(I+2) = DY(I+2) DY(I+2) = DTEMP 50 CONTINUE RETURN END