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

1.1       bertrand    1:       DOUBLE PRECISION FUNCTION DSDOT(N,SX,INCX,SY,INCY)
                      2: *     .. Scalar Arguments ..
                      3:       INTEGER INCX,INCY,N
                      4: *     ..
                      5: *     .. Array Arguments ..
                      6:       REAL SX(*),SY(*)
                      7: *     ..
                      8: *
                      9: *  AUTHORS
                     10: *  =======
                     11: *  Lawson, C. L., (JPL), Hanson, R. J., (SNLA), 
                     12: *  Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
                     13: *
                     14: *  Purpose
                     15: *  =======
                     16: *  Compute the inner product of two vectors with extended
                     17: *  precision accumulation and result.
                     18: *
                     19: *  Returns D.P. dot product accumulated in D.P., for S.P. SX and SY
                     20: *  DSDOT = sum for I = 0 to N-1 of  SX(LX+I*INCX) * SY(LY+I*INCY),
                     21: *  where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
                     22: *  defined in a similar way using INCY.
                     23: *
                     24: *  Arguments
                     25: *  =========
                     26: *
                     27: *  N      (input) INTEGER
                     28: *         number of elements in input vector(s)
                     29: *
                     30: *  SX     (input) REAL array, dimension(N)
                     31: *         single precision vector with N elements
                     32: *
                     33: *  INCX   (input) INTEGER
                     34: *          storage spacing between elements of SX
                     35: *
                     36: *  SY     (input) REAL array, dimension(N)
                     37: *         single precision vector with N elements
                     38: *
                     39: *  INCY   (input) INTEGER
                     40: *         storage spacing between elements of SY
                     41: *
                     42: *  DSDOT  (output) DOUBLE PRECISION
                     43: *         DSDOT  double precision dot product (zero if N.LE.0)
                     44: *
                     45: *  Further Details
                     46: *  ===============
                     47: *
                     48: *  REFERENCES
                     49: *      
                     50: *  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
                     51: *  Krogh, Basic linear algebra subprograms for Fortran
                     52: *  usage, Algorithm No. 539, Transactions on Mathematical
                     53: *  Software 5, 3 (September 1979), pp. 308-323.
                     54: *
                     55: *  REVISION HISTORY  (YYMMDD)
                     56: *
                     57: *  791001  DATE WRITTEN
                     58: *  890831  Modified array declarations.  (WRB)
                     59: *  890831  REVISION DATE from Version 3.2
                     60: *  891214  Prologue converted to Version 4.0 format.  (BAB)
                     61: *  920310  Corrected definition of LX in DESCRIPTION.  (WRB)
                     62: *  920501  Reformatted the REFERENCES section.  (WRB)
                     63: *  070118  Reformat to LAPACK style (JL)
                     64: *
                     65: *  =====================================================================
                     66: *
                     67: *     .. Local Scalars ..
                     68:       INTEGER I,KX,KY,NS
                     69: *     ..
                     70: *     .. Intrinsic Functions ..
                     71:       INTRINSIC DBLE
                     72: *     ..
                     73:       DSDOT = 0.0D0
                     74:       IF (N.LE.0) RETURN
                     75:       IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 20
                     76: *
                     77: *     Code for unequal or nonpositive increments.
                     78: *
                     79:       KX = 1
                     80:       KY = 1
                     81:       IF (INCX.LT.0) KX = 1 + (1-N)*INCX
                     82:       IF (INCY.LT.0) KY = 1 + (1-N)*INCY
                     83:       DO 10 I = 1,N
                     84:           DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
                     85:           KX = KX + INCX
                     86:           KY = KY + INCY
                     87:    10 CONTINUE
                     88:       RETURN
                     89: *
                     90: *     Code for equal, positive, non-unit increments.
                     91: *
                     92:    20 NS = N*INCX
                     93:       DO 30 I = 1,NS,INCX
                     94:           DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
                     95:    30 CONTINUE
                     96:       RETURN
                     97:       END