relibc_openlibm/slatec/sdsdot.f

*DECK SDSDOT
      REAL FUNCTION SDSDOT (N, SB, SX, INCX, SY, INCY)
C***BEGIN PROLOGUE  SDSDOT
C***PURPOSE  Compute the inner product of two vectors with extended
C            precision accumulation.
C***LIBRARY   SLATEC (BLAS)
C***CATEGORY  D1A4
C***TYPE      SINGLE PRECISION (SDSDOT-S, CDCDOT-C)
C***KEYWORDS  BLAS, DOT PRODUCT, INNER PRODUCT, LINEAR ALGEBRA, VECTOR
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       SB  single precision scalar to be added to inner product
C       SX  single precision vector with N elements
C     INCX  storage spacing between elements of SX
C       SY  single precision vector with N elements
C     INCY  storage spacing between elements of SY
C
C     --Output--
C   SDSDOT  single precision dot product (SB if N .LE. 0)
C
C     Returns S.P. result with dot product accumulated in D.P.
C     SDSDOT = SB + sum for I = 0 to N-1 of SX(LX+I*INCX)*SY(LY+I*INCY),
C     where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
C     defined in a similar way using INCY.
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  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   791001  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
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   920310  Corrected definition of LX in DESCRIPTION.  (WRB)
C   920501  Reformatted the REFERENCES section.  (WRB)
C***END PROLOGUE  SDSDOT
      REAL SX(*), SY(*), SB
      DOUBLE PRECISION DSDOT
C***FIRST EXECUTABLE STATEMENT  SDSDOT
      DSDOT = SB
      IF (N .LE. 0) GO TO 30
      IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 40
C
C     Code for unequal or nonpositive increments.
C
      KX = 1
      KY = 1
      IF (INCX .LT. 0) KX = 1+(1-N)*INCX
      IF (INCY .LT. 0) KY = 1+(1-N)*INCY
      DO 10 I = 1,N
        DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
        KX = KX + INCX
        KY = KY + INCY
   10 CONTINUE
   30 SDSDOT = DSDOT
      RETURN
C
C     Code for equal and positive increments.
C
   40 NS = N*INCX
      DO 50 I = 1,NS,INCX
        DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
   50 CONTINUE
      SDSDOT = DSDOT
      RETURN
      END