Revision **948ad5967298b4dc174f4d96511af60f38e9279e** authored by Roger Koenker on **27 July 2019, 09:38:23 UTC**, committed by cran-robot on **27 July 2019, 09:38:23 UTC**

iswap.f

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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
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