dsdot.c

Go to the documentation of this file.

/* dsdot.f -- translated by f2c (version 20061008).
   You must link the resulting object file with libf2c:
        on Microsoft Windows system, link with libf2c.lib;
        on Linux or Unix systems, link with .../path/to/libf2c.a -lm
        or, if you install libf2c.a in a standard place, with -lf2c -lm
        -- in that order, at the end of the command line, as in
                cc *.o -lf2c -lm
        Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

                http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"
#include "blaswrap.h"

doublereal dsdot_(integer *n, real *sx, integer *incx, real *sy, integer *
        incy)
{
    /* System generated locals */
    integer i__1, i__2;
    doublereal ret_val;

    /* Local variables */
    integer i__, ns, kx, ky;

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  AUTHORS */
/*  ======= */
/*  Lawson, C. L., (JPL), Hanson, R. J., (SNLA), */
/*  Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL) */

/*  Purpose */
/*  ======= */
/*  Compute the inner product of two vectors with extended */
/*  precision accumulation and result. */

/*  Returns D.P. dot product accumulated in D.P., for S.P. SX and SY */
/*  DSDOT = sum for I = 0 to N-1 of  SX(LX+I*INCX) * SY(LY+I*INCY), */
/*  where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is */
/*  defined in a similar way using INCY. */

/*  Arguments */
/*  ========= */

/*  N      (input) INTEGER */
/*         number of elements in input vector(s) */

/*  SX     (input) REAL array, dimension(N) */
/*         single precision vector with N elements */

/*  INCX   (input) INTEGER */
/*          storage spacing between elements of SX */

/*  SY     (input) REAL array, dimension(N) */
/*         single precision vector with N elements */

/*  INCY   (input) INTEGER */
/*         storage spacing between elements of SY */

/*  DSDOT  (output) DOUBLE PRECISION */
/*         DSDOT  double precision dot product (zero if N.LE.0) */

/*  REFERENCES */
/*  ========== */

/*  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T. */
/*  Krogh, Basic linear algebra subprograms for Fortran */
/*  usage, Algorithm No. 539, Transactions on Mathematical */
/*  Software 5, 3 (September 1979), pp. 308-323. */

/*  REVISION HISTORY  (YYMMDD) */
/*  ========================== */

/*  791001  DATE WRITTEN */
/*  890831  Modified array declarations.  (WRB) */
/*  890831  REVISION DATE from Version 3.2 */
/*  891214  Prologue converted to Version 4.0 format.  (BAB) */
/*  920310  Corrected definition of LX in DESCRIPTION.  (WRB) */
/*  920501  Reformatted the REFERENCES section.  (WRB) */
/*  070118  Reformat to LAPACK style (JL) */

/*  ===================================================================== */

/*     .. Local Scalars .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
    /* Parameter adjustments */
    --sy;
    --sx;

    /* Function Body */
    ret_val = 0.;
    if (*n <= 0) {
        return ret_val;
    }
    if (*incx == *incy && *incx > 0) {
        goto L20;
    }

/*     Code for unequal or nonpositive increments. */

    kx = 1;
    ky = 1;
    if (*incx < 0) {
        kx = (1 - *n) * *incx + 1;
    }
    if (*incy < 0) {
        ky = (1 - *n) * *incy + 1;
    }
    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
        ret_val += (doublereal) sx[kx] * (doublereal) sy[ky];
        kx += *incx;
        ky += *incy;
/* L10: */
    }
    return ret_val;

/*     Code for equal, positive, non-unit increments. */

L20:
    ns = *n * *incx;
    i__1 = ns;
    i__2 = *incx;
    for (i__ = 1; i__2 < 0 ? i__ >= i__1 : i__ <= i__1; i__ += i__2) {
        ret_val += (doublereal) sx[i__] * (doublereal) sy[i__];
/* L30: */
    }
    return ret_val;
} /* dsdot_ */