Annotation of rpl/lapack/blas/ddot.f, revision 1.2
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
33: IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
34: *
35: * code for unequal increments or equal increments
36: * not equal to 1
37: *
38: IX = 1
39: IY = 1
40: IF (INCX.LT.0) IX = (-N+1)*INCX + 1
41: IF (INCY.LT.0) IY = (-N+1)*INCY + 1
42: DO 10 I = 1,N
43: DTEMP = DTEMP + DX(IX)*DY(IY)
44: IX = IX + INCX
45: IY = IY + INCY
46: 10 CONTINUE
47: DDOT = DTEMP
48: RETURN
49: *
50: * code for both increments equal to 1
51: *
52: *
53: * clean-up loop
54: *
55: 20 M = MOD(N,5)
56: IF (M.EQ.0) GO TO 40
57: DO 30 I = 1,M
58: DTEMP = DTEMP + DX(I)*DY(I)
59: 30 CONTINUE
60: IF (N.LT.5) GO TO 60
61: 40 MP1 = M + 1
62: DO 50 I = MP1,N,5
63: DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
64: + DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
65: 50 CONTINUE
66: 60 DDOT = DTEMP
67: RETURN
68: END
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