drscl.c

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/* DRSCL.F -- translated by f2c (version 19941215).
   You must link the resulting object file with the libraries:
        -lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Subroutine */ int drscl_(n, sa, sx, incx)
integer *n;
doublereal *sa, *sx;
integer *incx;
{
    static doublereal cden;
    static logical done;
    static doublereal cnum, cden1, cnum1;
    extern /* Subroutine */ int dscal_(), dlabad_();
    extern doublereal dlamch_();
    static doublereal bignum, smlnum, mul;


/*  -- LAPACK auxiliary routine (version 1.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/*     Courant Institute, Argonne National Lab, and Rice University */
/*     October 31, 1992 */

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

/*  Purpose */
/*  ======= */

/*  DRSCL multiplies an n-element real vector x by the real scalar 1/a. */
/*  This is done without overflow or underflow as long as */
/*  the final result x/a does not overflow or underflow. */

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

/*  N       (input) INTEGER */
/*          The number of components of the vector x. */

/*  SA      (input) DOUBLE PRECISION */
/*          The scalar a which is used to divide each component of x. */
/*          SA must be >= 0, or the subroutine will divide by zero. */

/*  SX      (input/output) DOUBLE PRECISION array, dimension */
/*                         (1+(N-1)*abs(INCX)) */
/*          The n-element vector x. */

/*  INCX    (input) INTEGER */
/*          The increment between successive values of the vector SX. */
/*          > 0:  SX(1) = X(1) and SX(1+(i-1)*INCX) = x(i),     1< i<= n 
*/
/*          < 0:  SX(1) = X(n) and SX(1+(i-1)*INCX) = x(n-i+1), 1< i<= n 
*/

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

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

/*     Quick return if possible */

    /* Parameter adjustments */
    --sx;

    /* Function Body */
    if (*n <= 0) {
        return 0;
    }

/*     Get machine parameters */

    smlnum = dlamch_("S", 1L);
    bignum = 1. / smlnum;
    dlabad_(&smlnum, &bignum);

/*     Initialize the denominator to SA and the numerator to 1. */

    cden = *sa;
    cnum = 1.;

L10:
    cden1 = cden * smlnum;
    cnum1 = cnum / bignum;
    if (abs(cden1) > abs(cnum) && cnum != 0.) {

/*        Pre-multiply X by SMLNUM if CDEN is large compared to CNUM. 
*/

        mul = smlnum;
        done = FALSE_;
        cden = cden1;
    } else if (abs(cnum1) > abs(cden)) {

/*        Pre-multiply X by BIGNUM if CDEN is small compared to CNUM. 
*/

        mul = bignum;
        done = FALSE_;
        cnum = cnum1;
    } else {

/*        Multiply X by CNUM / CDEN and return. */

        mul = cnum / cden;
        done = TRUE_;
    }

/*     Scale the vector X by MUL */

    dscal_(n, &mul, &sx[1], incx);

    if (! done) {
        goto L10;
    }

    return 0;

/*     End of DRSCL */

} /* drscl_ */

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