Annotation of rpl/lapack/blas/ddot.f, revision 1.7
1.1 bertrand 1: DOUBLE PRECISION FUNCTION DDOT(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: * DDOT forms the dot product of two vectors.
13: * uses unrolled loops for increments equal to 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: DDOT = 0.0d0
31: DTEMP = 0.0d0
32: IF (N.LE.0) RETURN
1.7 ! bertrand 33: IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
1.1 bertrand 34: *
35: * code for both increments equal to 1
36: *
37: *
38: * clean-up loop
39: *
1.7 ! bertrand 40: M = MOD(N,5)
! 41: IF (M.NE.0) THEN
! 42: DO I = 1,M
! 43: DTEMP = DTEMP + DX(I)*DY(I)
! 44: END DO
! 45: IF (N.LT.5) THEN
! 46: DDOT=DTEMP
! 47: RETURN
! 48: END IF
! 49: END IF
! 50: MP1 = M + 1
! 51: DO I = MP1,N,5
1.1 bertrand 52: DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
1.7 ! bertrand 53: $ DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
! 54: END DO
! 55: ELSE
! 56: *
! 57: * code for unequal increments or equal increments
! 58: * not equal to 1
! 59: *
! 60: IX = 1
! 61: IY = 1
! 62: IF (INCX.LT.0) IX = (-N+1)*INCX + 1
! 63: IF (INCY.LT.0) IY = (-N+1)*INCY + 1
! 64: DO I = 1,N
! 65: DTEMP = DTEMP + DX(IX)*DY(IY)
! 66: IX = IX + INCX
! 67: IY = IY + INCY
! 68: END DO
! 69: END IF
! 70: DDOT = DTEMP
1.1 bertrand 71: RETURN
72: END
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