agent_compositor_test/references/igraph-1.0.1/vendor/lapack/dlartg.c

/*  -- translated by f2c (version 20240504).
   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"

/* > \brief \b DLARTG generates a plane rotation with real cosine and real sine.   

    =========== DOCUMENTATION ===========   

   Online html documentation available at   
              http://www.netlib.org/lapack/explore-html/   

   > \htmlonly   
   > Download DLARTG + dependencies   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlartg.
f">   
   > [TGZ]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlartg.
f">   
   > [ZIP]</a>   
   > <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlartg.
f">   
   > [TXT]</a>   
   > \endhtmlonly   

    Definition:   
    ===========   

         SUBROUTINE DLARTG( F, G, CS, SN, R )   

         DOUBLE PRECISION   CS, F, G, R, SN   


   > \par Purpose:   
    =============   
   >   
   > \verbatim   
   >   
   > DLARTG generate a plane rotation so that   
   >   
   >    [  CS  SN  ]  .  [ F ]  =  [ R ]   where CS**2 + SN**2 = 1.   
   >    [ -SN  CS  ]     [ G ]     [ 0 ]   
   >   
   > This is a slower, more accurate version of the BLAS1 routine DROTG,   
   > with the following other differences:   
   >    F and G are unchanged on return.   
   >    If G=0, then CS=1 and SN=0.   
   >    If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any   
   >       floating point operations (saves work in DBDSQR when   
   >       there are zeros on the diagonal).   
   >   
   > If F exceeds G in magnitude, CS will be positive.   
   > \endverbatim   

    Arguments:   
    ==========   

   > \param[in] F   
   > \verbatim   
   >          F is DOUBLE PRECISION   
   >          The first component of vector to be rotated.   
   > \endverbatim   
   >   
   > \param[in] G   
   > \verbatim   
   >          G is DOUBLE PRECISION   
   >          The second component of vector to be rotated.   
   > \endverbatim   
   >   
   > \param[out] CS   
   > \verbatim   
   >          CS is DOUBLE PRECISION   
   >          The cosine of the rotation.   
   > \endverbatim   
   >   
   > \param[out] SN   
   > \verbatim   
   >          SN is DOUBLE PRECISION   
   >          The sine of the rotation.   
   > \endverbatim   
   >   
   > \param[out] R   
   > \verbatim   
   >          R is DOUBLE PRECISION   
   >          The nonzero component of the rotated vector.   
   >   
   >  This version has a few statements commented out for thread safety   
   >  (machine parameters are computed on each entry). 10 feb 03, SJH.   
   > \endverbatim   

    Authors:   
    ========   

   > \author Univ. of Tennessee   
   > \author Univ. of California Berkeley   
   > \author Univ. of Colorado Denver   
   > \author NAG Ltd.   

   > \date September 2012   

   > \ingroup auxOTHERauxiliary   

    =====================================================================   
   Subroutine */ int igraphdlartg_(doublereal *f, doublereal *g, doublereal *cs, 
	doublereal *sn, doublereal *r__)
{
    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2;

    /* Builtin functions */
    double log(doublereal), pow_di(doublereal *, integer *), sqrt(doublereal);

    /* Local variables */
    integer i__;
    doublereal f1, g1, eps, scale;
    integer count;
    doublereal safmn2, safmx2;
    extern doublereal igraphdlamch_(char *);
    doublereal safmin;


/*  -- LAPACK auxiliary routine (version 3.4.2) --   
    -- LAPACK is a software package provided by Univ. of Tennessee,    --   
    -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--   
       September 2012   


    =====================================================================   

       LOGICAL            FIRST   
       SAVE               FIRST, SAFMX2, SAFMIN, SAFMN2   
       DATA               FIRST / .TRUE. /   

       IF( FIRST ) THEN */
    safmin = igraphdlamch_("S");
    eps = igraphdlamch_("E");
    d__1 = igraphdlamch_("B");
    i__1 = (integer) (log(safmin / eps) / log(igraphdlamch_("B")) / 2.);
    safmn2 = pow_di(&d__1, &i__1);
    safmx2 = 1. / safmn2;
/*        FIRST = .FALSE.   
       END IF */
    if (*g == 0.) {
	*cs = 1.;
	*sn = 0.;
	*r__ = *f;
    } else if (*f == 0.) {
	*cs = 0.;
	*sn = 1.;
	*r__ = *g;
    } else {
	f1 = *f;
	g1 = *g;
/* Computing MAX */
	d__1 = abs(f1), d__2 = abs(g1);
	scale = max(d__1,d__2);
	if (scale >= safmx2) {
	    count = 0;
L10:
	    ++count;
	    f1 *= safmn2;
	    g1 *= safmn2;
/* Computing MAX */
	    d__1 = abs(f1), d__2 = abs(g1);
	    scale = max(d__1,d__2);
	    if (scale >= safmx2) {
		goto L10;
	    }
/* Computing 2nd power */
	    d__1 = f1;
/* Computing 2nd power */
	    d__2 = g1;
	    *r__ = sqrt(d__1 * d__1 + d__2 * d__2);
	    *cs = f1 / *r__;
	    *sn = g1 / *r__;
	    i__1 = count;
	    for (i__ = 1; i__ <= i__1; ++i__) {
		*r__ *= safmx2;
/* L20: */
	    }
	} else if (scale <= safmn2) {
	    count = 0;
L30:
	    ++count;
	    f1 *= safmx2;
	    g1 *= safmx2;
/* Computing MAX */
	    d__1 = abs(f1), d__2 = abs(g1);
	    scale = max(d__1,d__2);
	    if (scale <= safmn2) {
		goto L30;
	    }
/* Computing 2nd power */
	    d__1 = f1;
/* Computing 2nd power */
	    d__2 = g1;
	    *r__ = sqrt(d__1 * d__1 + d__2 * d__2);
	    *cs = f1 / *r__;
	    *sn = g1 / *r__;
	    i__1 = count;
	    for (i__ = 1; i__ <= i__1; ++i__) {
		*r__ *= safmn2;
/* L40: */
	    }
	} else {
/* Computing 2nd power */
	    d__1 = f1;
/* Computing 2nd power */
	    d__2 = g1;
	    *r__ = sqrt(d__1 * d__1 + d__2 * d__2);
	    *cs = f1 / *r__;
	    *sn = g1 / *r__;
	}
	if (abs(*f) > abs(*g) && *cs < 0.) {
	    *cs = -(*cs);
	    *sn = -(*sn);
	    *r__ = -(*r__);
	}
    }
    return 0;

/*     End of DLARTG */

} /* igraphdlartg_ */