snrm2.c

/* snrm2.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 "clapack.h"


doublereal snrm2_(integer *n, real *x, integer *incx)
{
    /* System generated locals */
    integer i__1, i__2;
    real ret_val, r__1;

    /* Builtin functions */
    double sqrt(doublereal);

    /* Local variables */
    integer ix;
    real ssq, norm, scale, absxi;

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

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

/*  SNRM2 returns the euclidean norm of a vector via the function */
/*  name, so that */

/*     SNRM2 := sqrt( x'*x ). */

/*  Further Details */
/*  =============== */

/*  -- This version written on 25-October-1982. */
/*     Modified on 14-October-1993 to inline the call to SLASSQ. */
/*     Sven Hammarling, Nag Ltd. */


/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
    /* Parameter adjustments */
    --x;

    /* Function Body */
    if (*n < 1 || *incx < 1) {
	norm = 0.f;
    } else if (*n == 1) {
	norm = dabs(x[1]);
    } else {
	scale = 0.f;
	ssq = 1.f;
/*        The following loop is equivalent to this call to the LAPACK */
/*        auxiliary routine: */
/*        CALL SLASSQ( N, X, INCX, SCALE, SSQ ) */

	i__1 = (*n - 1) * *incx + 1;
	i__2 = *incx;
	for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
	    if (x[ix] != 0.f) {
		absxi = (r__1 = x[ix], dabs(r__1));
		if (scale < absxi) {
/* Computing 2nd power */
		    r__1 = scale / absxi;
		    ssq = ssq * (r__1 * r__1) + 1.f;
		    scale = absxi;
		} else {
/* Computing 2nd power */
		    r__1 = absxi / scale;
		    ssq += r__1 * r__1;
		}
	    }
/* L10: */
	}
	norm = scale * sqrt(ssq);
    }

    ret_val = norm;
    return ret_val;

/*     End of SNRM2. */

} /* snrm2_ */