trunk/blas/dswap.f

      SUBROUTINE  DSWAP (N,DX,INCX,DY,INCY)
C
C     INTERCHANGES TWO VECTORS.
C     USES UNROLLED LOOPS FOR INCREMENTS EQUAL ONE.
C     JACK DONGARRA, LINPACK, 3/11/78.
C
      DOUBLE PRECISION DX(*),DY(*),DTEMP
      INTEGER I,INCX,INCY,IX,IY,M,MP1,N
C
      IF(N.LE.0)RETURN
      IF(INCX.EQ.1.AND.INCY.EQ.1)GO TO 20
C
C       CODE FOR UNEQUAL INCREMENTS OR EQUAL INCREMENTS NOT EQUAL
C         TO 1
C
      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
C
C       CODE FOR BOTH INCREMENTS EQUAL TO 1
C
C
C       CLEAN-UP LOOP
C
   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
1	SUBROUTINE DSWAP (N,DX,INCX,DY,INCY)
2	C
3	C INTERCHANGES TWO VECTORS.
4	C USES UNROLLED LOOPS FOR INCREMENTS EQUAL ONE.
5	C JACK DONGARRA, LINPACK, 3/11/78.
6	C
7	DOUBLE PRECISION DX(),DY(),DTEMP
8	INTEGER I,INCX,INCY,IX,IY,M,MP1,N
9	C
10	IF(N.LE.0)RETURN
11	IF(INCX.EQ.1.AND.INCY.EQ.1)GO TO 20
12	C
13	C CODE FOR UNEQUAL INCREMENTS OR EQUAL INCREMENTS NOT EQUAL
14	C TO 1
15	C
16	IX = 1
17	IY = 1
18	IF(INCX.LT.0)IX = (-N+1)*INCX + 1
19	IF(INCY.LT.0)IY = (-N+1)*INCY + 1
20	DO 10 I = 1,N
21	DTEMP = DX(IX)
22	DX(IX) = DY(IY)
23	DY(IY) = DTEMP
24	IX = IX + INCX
25	IY = IY + INCY
26	10 CONTINUE
27	RETURN
28	C
29	C CODE FOR BOTH INCREMENTS EQUAL TO 1
30	C
31	C
32	C CLEAN-UP LOOP
33	C
34	20 M = MOD(N,3)
35	IF( M .EQ. 0 ) GO TO 40
36	DO 30 I = 1,M
37	DTEMP = DX(I)
38	DX(I) = DY(I)
39	DY(I) = DTEMP
40	30 CONTINUE
41	IF( N .LT. 3 ) RETURN
42	40 MP1 = M + 1
43	DO 50 I = MP1,N,3
44	DTEMP = DX(I)
45	DX(I) = DY(I)
46	DY(I) = DTEMP
47	DTEMP = DX(I + 1)
48	DX(I + 1) = DY(I + 1)
49	DY(I + 1) = DTEMP
50	DTEMP = DX(I + 2)
51	DX(I + 2) = DY(I + 2)
52	DY(I + 2) = DTEMP
53	50 CONTINUE
54	RETURN
55	END