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Annotation of rpl/lapack/blas/ddot.f, revision 1.3

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