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

/* Subroutine */ int clarfg_(integer *n, complex *alpha, complex *x, integer *
	incx, complex *tau)
{
/*  -- LAPACK auxiliary routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       September 30, 1994   


    Purpose   
    =======   

    CLARFG generates a complex elementary reflector H of order n, such   
    that   

          H' * ( alpha ) = ( beta ),   H' * H = I.   
               (   x   )   (   0  )   

    where alpha and beta are scalars, with beta real, and x is an   
    (n-1)-element complex vector. H is represented in the form   

          H = I - tau * ( 1 ) * ( 1 v' ) ,   
                        ( v )   

    where tau is a complex scalar and v is a complex (n-1)-element   
    vector. Note that H is not hermitian.   

    If the elements of x are all zero and alpha is real, then tau = 0   
    and H is taken to be the unit matrix.   

    Otherwise  1 <= real(tau) <= 2  and  abs(tau-1) <= 1 .   

    Arguments   
    =========   

    N       (input) INTEGER   
            The order of the elementary reflector.   

    ALPHA   (input/output) COMPLEX   
            On entry, the value alpha.   
            On exit, it is overwritten with the value beta.   

    X       (input/output) COMPLEX array, dimension   
                           (1+(N-2)*abs(INCX))   
            On entry, the vector x.   
            On exit, it is overwritten with the vector v.   

    INCX    (input) INTEGER   
            The increment between elements of X. INCX > 0.   

    TAU     (output) COMPLEX   
            The value tau.   

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


       Parameter adjustments */
    /* Table of constant values */
    static complex c_b5 = {1.f,0.f};
    
    /* System generated locals */
    integer i__1;
    real r__1, r__2;
    complex q__1, q__2;
    /* Builtin functions */
    double r_imag(complex *), r_sign(real *, real *);
    /* Local variables */
    static real beta;
    static integer j;
    extern /* Subroutine */ int cscal_(integer *, complex *, complex *, 
	    integer *);
    static real alphi, alphr, xnorm;
    extern doublereal scnrm2_(integer *, complex *, integer *), slapy3_(real *
	    , real *, real *);
    extern /* Complex */ VOID cladiv_(complex *, complex *, complex *);
    extern doublereal slamch_(char *);
    extern /* Subroutine */ int csscal_(integer *, real *, complex *, integer 
	    *);
    static real safmin, rsafmn;
    static integer knt;


    --x;

    /* Function Body */
    if (*n <= 0) {
	tau->r = 0.f, tau->i = 0.f;
	return 0;
    }

    i__1 = *n - 1;
    xnorm = scnrm2_(&i__1, &x[1], incx);
    alphr = alpha->r;
    alphi = r_imag(alpha);

    if (xnorm == 0.f && alphi == 0.f) {

/*        H  =  I */

	tau->r = 0.f, tau->i = 0.f;
    } else {

/*        general case */

	r__1 = slapy3_(&alphr, &alphi, &xnorm);
	beta = -r_sign(&r__1, &alphr);
	safmin = slamch_("S") / slamch_("E");
	rsafmn = 1.f / safmin;

	if (dabs(beta) < safmin) {

/*           XNORM, BETA may be inaccurate; scale X and recompute them */

	    knt = 0;
L10:
	    ++knt;
	    i__1 = *n - 1;
	    csscal_(&i__1, &rsafmn, &x[1], incx);
	    beta *= rsafmn;
	    alphi *= rsafmn;
	    alphr *= rsafmn;
	    if (dabs(beta) < safmin) {
		goto L10;
	    }

/*           New BETA is at most 1, at least SAFMIN */

	    i__1 = *n - 1;
	    xnorm = scnrm2_(&i__1, &x[1], incx);
	    q__1.r = alphr, q__1.i = alphi;
	    alpha->r = q__1.r, alpha->i = q__1.i;
	    r__1 = slapy3_(&alphr, &alphi, &xnorm);
	    beta = -r_sign(&r__1, &alphr);
	    r__1 = (beta - alphr) / beta;
	    r__2 = -alphi / beta;
	    q__1.r = r__1, q__1.i = r__2;
	    tau->r = q__1.r, tau->i = q__1.i;
	    q__2.r = alpha->r - beta, q__2.i = alpha->i;
	    cladiv_(&q__1, &c_b5, &q__2);
	    alpha->r = q__1.r, alpha->i = q__1.i;
	    i__1 = *n - 1;
	    cscal_(&i__1, alpha, &x[1], incx);

/*           If ALPHA is subnormal, it may lose relative accuracy */

	    alpha->r = beta, alpha->i = 0.f;
	    i__1 = knt;
	    for (j = 1; j <= i__1; ++j) {
		q__1.r = safmin * alpha->r, q__1.i = safmin * alpha->i;
		alpha->r = q__1.r, alpha->i = q__1.i;
/* L20: */
	    }
	} else {
	    r__1 = (beta - alphr) / beta;
	    r__2 = -alphi / beta;
	    q__1.r = r__1, q__1.i = r__2;
	    tau->r = q__1.r, tau->i = q__1.i;
	    q__2.r = alpha->r - beta, q__2.i = alpha->i;
	    cladiv_(&q__1, &c_b5, &q__2);
	    alpha->r = q__1.r, alpha->i = q__1.i;
	    i__1 = *n - 1;
	    cscal_(&i__1, alpha, &x[1], incx);
	    alpha->r = beta, alpha->i = 0.f;
	}
    }

    return 0;

/*     End of CLARFG */

} /* clarfg_ */

