Annotation of rpl/lapack/blas/dswap.f, revision 1.7
1.1 bertrand 1: SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
2: * .. Scalar Arguments ..
3: INTEGER INCX,INCY,N
4: * ..
5: * .. Array Arguments ..
6: DOUBLE PRECISION DX(*),DY(*)
7: * ..
8: *
9: * Purpose
10: * =======
11: *
12: * interchanges two vectors.
13: * uses unrolled loops for increments equal one.
14: *
15: * Further Details
16: * ===============
17: *
18: * jack dongarra, linpack, 3/11/78.
19: * modified 12/3/93, array(1) declarations changed to array(*)
20: *
21: * =====================================================================
22: *
23: * .. Local Scalars ..
24: DOUBLE PRECISION DTEMP
25: INTEGER I,IX,IY,M,MP1
26: * ..
27: * .. Intrinsic Functions ..
28: INTRINSIC MOD
29: * ..
30: IF (N.LE.0) RETURN
1.7 ! bertrand 31: IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
1.1 bertrand 32: *
1.7 ! bertrand 33: * code for both increments equal to 1
1.1 bertrand 34: *
35: *
1.7 ! bertrand 36: * clean-up loop
1.1 bertrand 37: *
1.7 ! bertrand 38: M = MOD(N,3)
! 39: IF (M.NE.0) THEN
! 40: DO I = 1,M
! 41: DTEMP = DX(I)
! 42: DX(I) = DY(I)
! 43: DY(I) = DTEMP
! 44: END DO
! 45: IF (N.LT.3) RETURN
! 46: END IF
! 47: MP1 = M + 1
! 48: DO I = MP1,N,3
! 49: DTEMP = DX(I)
! 50: DX(I) = DY(I)
! 51: DY(I) = DTEMP
! 52: DTEMP = DX(I+1)
! 53: DX(I+1) = DY(I+1)
! 54: DY(I+1) = DTEMP
! 55: DTEMP = DX(I+2)
! 56: DX(I+2) = DY(I+2)
! 57: DY(I+2) = DTEMP
! 58: END DO
! 59: ELSE
1.1 bertrand 60: *
1.7 ! bertrand 61: * code for unequal increments or equal increments not equal
! 62: * to 1
1.1 bertrand 63: *
1.7 ! bertrand 64: IX = 1
! 65: IY = 1
! 66: IF (INCX.LT.0) IX = (-N+1)*INCX + 1
! 67: IF (INCY.LT.0) IY = (-N+1)*INCY + 1
! 68: DO I = 1,N
! 69: DTEMP = DX(IX)
! 70: DX(IX) = DY(IY)
! 71: DY(IY) = DTEMP
! 72: IX = IX + INCX
! 73: IY = IY + INCY
! 74: END DO
! 75: END IF
1.1 bertrand 76: RETURN
77: END
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