SUBROUTINE ISWAP (N, IX, INCX, IY, INCY) C***AUTHOR Vandevender, W. H., (SNLA) C***DESCRIPTION C C Extended B L A S Subprogram C Description of Parameters C C --Input-- C N number of elements in input vector(s) C IX integer vector with N elements C INCX storage spacing between elements of IX C IY integer vector with N elements C INCY storage spacing between elements of IY C C --Output-- C IX input vector IY (unchanged if N .LE. 0) C IY input vector IX (unchanged if N .LE. 0) C C Interchange integer IX and integer IY. C For I = 0 to N-1, interchange IX(LX+I*INCX) and IY(LY+I*INCY), C where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is C defined in a similar way using INCY. C C***REFERENCES C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T. C Krogh, Basic linear algebra subprograms for Fortran C usage, Algorithm No. 539, Transactions on Mathematical C Software 5, 3 (September 1979), pp. 308-323. C***ROUTINES CALLED (NONE) C***REVISION HISTORY (YYMMDD) C 850601 DATE WRITTEN C 861211 REVISION DATE from Version 3.2 C 891214 Prologue converted to Version 4.0 format. (BAB) C 920310 Corrected definition of LX in DESCRIPTION. (WRB) C 920501 Reformatted the REFERENCES section. (WRB) C***END PROLOGUE ISWAP INTEGER IX(*), IY(*), ITEMP1, ITEMP2, ITEMP3 C***FIRST EXECUTABLE STATEMENT ISWAP IF (N .LE. 0) RETURN IF (INCX .NE. INCY) GO TO 5 IF (INCX-1) 5,20,60 C C Code for unequal or nonpositive increments. C 5 IIX = 1 IIY = 1 IF (INCX .LT. 0) IIX = (1-N)*INCX + 1 IF (INCY .LT. 0) IIY = (1-N)*INCY + 1 DO 10 I = 1,N ITEMP1 = IX(IIX) IX(IIX) = IY(IIY) IY(IIY) = ITEMP1 IIX = IIX + INCX IIY = IIY + INCY 10 CONTINUE RETURN C C Code for both increments equal to 1. C C Clean-up loop so remaining vector length is a multiple of 3. C 20 M = MOD(N,3) IF (M .EQ. 0) GO TO 40 DO 30 I = 1,M ITEMP1 = IX(I) IX(I) = IY(I) IY(I) = ITEMP1 30 CONTINUE IF (N .LT. 3) RETURN 40 MP1 = M + 1 DO 50 I = MP1,N,3 ITEMP1 = IX(I) ITEMP2 = IX(I+1) ITEMP3 = IX(I+2) IX(I) = IY(I) IX(I+1) = IY(I+1) IX(I+2) = IY(I+2) IY(I) = ITEMP1 IY(I+1) = ITEMP2 IY(I+2) = ITEMP3 50 CONTINUE RETURN C C Code for equal, positive, non-unit increments. C 60 NS = N*INCX DO 70 I = 1,NS,INCX ITEMP1 = IX(I) IX(I) = IY(I) IY(I) = ITEMP1 70 CONTINUE RETURN END