relibc_openlibm/slatec/dqdoti.f

*DECK DQDOTI
      DOUBLE PRECISION FUNCTION DQDOTI (N, DB, QC, DX, INCX, DY, INCY)
C***BEGIN PROLOGUE  DQDOTI
C***PURPOSE  Compute the inner product of two vectors with extended
C            precision accumulation and result.
C***LIBRARY   SLATEC
C***CATEGORY  D1A4
C***TYPE      DOUBLE PRECISION (DQDOTI-D)
C***KEYWORDS  DOT PRODUCT, INNER PRODUCT
C***AUTHOR  Lawson, C. L., (JPL)
C           Hanson, R. J., (SNLA)
C           Kincaid, D. R., (U. of Texas)
C           Krogh, F. T., (JPL)
C***DESCRIPTION
C
C                B L A S  Subprogram
C    Description of parameters
C
C     --Input--
C        N  number of elements in input vector(s)
C       DB  double precision scalar to be added to inner product
C       QC  extended precision scalar to be added
C       DX  double precision vector with N elements
C     INCX  storage spacing between elements of DX
C       DY  double precision vector with N elements
C     INCY  storage spacing between elements of DY
C
C     --Output--
C   DQDOTI  double precision result
C       QC  extended precision result
C
C     D.P. dot product with extended precision accumulation (and result)
C     QC and DQDOTI are set = DB + sum for I = 0 to N-1 of
C       DX(LX+I*INCX) * DY(LY+I*INCY),  where QC is an extended
C       precision result which can be used as input to DQDOTA,
C       and LX = 1 if INCX .GE. 0, else LX = (-INCX)*N, and LY is
C       defined in a similar way using INCY.  The MP package by
C       Richard P. Brent is used for the extended precision arithmetic.
C
C     Fred T. Krogh,  JPL,  1977,  June 1
C
C     The common block for the MP package is named MPCOM.  If local
C     variable I1 is zero, DQDOTI calls MPBLAS to initialize the MP
C     package and reset I1 to 1.
C
C    The argument QC(*), and the local variables QX and QY are INTEGER
C    arrays of size 30.  See the comments in the routine MPBLAS for the
C    reason for this choice.
C
C***REFERENCES  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
C                 Krogh, Basic linear algebra subprograms for Fortran
C                 usage, Algorithm No. 539, Transactions on Mathematical
C                 Software 5, 3 (September 1979), pp. 308-323.
C***ROUTINES CALLED  MPADD, MPBLAS, MPCDM, MPCMD, MPMUL
C***COMMON BLOCKS    MPCOM
C***REVISION HISTORY  (YYMMDD)
C   791001  DATE WRITTEN
C   890831  Modified array declarations.  (WRB)
C   890831  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   920501  Reformatted the REFERENCES section.  (WRB)
C   930124  Increased Array sizes for SUN -r8.  (RWC)
C***END PROLOGUE  DQDOTI
      DOUBLE PRECISION DX(*), DY(*), DB
      INTEGER  QC(30), QX(30), QY(30)
      COMMON /MPCOM/  MPB, MPT, MPM, MPLUN, MPMXR, MPR(30)
      SAVE I1
      DATA  I1 / 0 /
C***FIRST EXECUTABLE STATEMENT  DQDOTI
      IF (I1 .EQ. 0) CALL MPBLAS(I1)
      QC(1) = 0
      IF (DB .EQ. 0.D0) GO TO 60
      CALL MPCDM(DB, QX)
      CALL MPADD(QC, QX, QC)
   60 IF (N .EQ. 0) GO TO 80
      IX = 1
      IY = 1
      IF (INCX .LT. 0) IX = (-N + 1) * INCX + 1
      IF (INCY .LT. 0) IY = (-N + 1) * INCY + 1
      DO  70  I = 1,N
         CALL MPCDM(DX(IX), QX)
         CALL MPCDM(DY(IY), QY)
         CALL MPMUL(QX, QY, QX)
         CALL MPADD(QC, QX, QC)
         IX = IX + INCX
         IY = IY + INCY
   70 CONTINUE
   80 CALL MPCMD(QC, DQDOTI)
      RETURN
      END