hypre/lapack/dlasq5.c

#include "hypre_lapack.h"
#include "f2c.h"

/* Subroutine */ int dlasq5_(integer *i0, integer *n0, doublereal *z__, 
	integer *pp, doublereal *tau, doublereal *dmin__, doublereal *dmin1, 
	doublereal *dmin2, doublereal *dn, doublereal *dnm1, doublereal *dnm2,
	 logical *ieee)
{
/*  -- LAPACK auxiliary routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       May 17, 2000   


    Purpose   
    =======   

    DLASQ5 computes one dqds transform in ping-pong form, one   
    version for IEEE machines another for non IEEE machines.   

    Arguments   
    =========   

    I0    (input) INTEGER   
          First index.   

    N0    (input) INTEGER   
          Last index.   

    Z     (input) DOUBLE PRECISION array, dimension ( 4*N )   
          Z holds the qd array. EMIN is stored in Z(4*N0) to avoid   
          an extra argument.   

    PP    (input) INTEGER   
          PP=0 for ping, PP=1 for pong.   

    TAU   (input) DOUBLE PRECISION   
          This is the shift.   

    DMIN  (output) DOUBLE PRECISION   
          Minimum value of d.   

    DMIN1 (output) DOUBLE PRECISION   
          Minimum value of d, excluding D( N0 ).   

    DMIN2 (output) DOUBLE PRECISION   
          Minimum value of d, excluding D( N0 ) and D( N0-1 ).   

    DN    (output) DOUBLE PRECISION   
          d(N0), the last value of d.   

    DNM1  (output) DOUBLE PRECISION   
          d(N0-1).   

    DNM2  (output) DOUBLE PRECISION   
          d(N0-2).   

    IEEE  (input) LOGICAL   
          Flag for IEEE or non IEEE arithmetic.   

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


       Parameter adjustments */
    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2;
    /* Local variables */
    static doublereal emin, temp, d__;
    static integer j4, j4p2;

    --z__;

    /* Function Body */
    if (*n0 - *i0 - 1 <= 0) {
	return 0;
    }

    j4 = (*i0 << 2) + *pp - 3;
    emin = z__[j4 + 4];
    d__ = z__[j4] - *tau;
    *dmin__ = d__;
    *dmin1 = -z__[j4];

    if (*ieee) {

/*        Code for IEEE arithmetic. */

	if (*pp == 0) {
	    i__1 = (*n0 - 3) << 2;
	    for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
		z__[j4 - 2] = d__ + z__[j4 - 1];
		temp = z__[j4 + 1] / z__[j4 - 2];
		d__ = d__ * temp - *tau;
		*dmin__ = min(*dmin__,d__);
		z__[j4] = z__[j4 - 1] * temp;
/* Computing MIN */
		d__1 = z__[j4];
		emin = min(d__1,emin);
/* L10: */
	    }
	} else {
	    i__1 = (*n0 - 3) << 2;
	    for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
		z__[j4 - 3] = d__ + z__[j4];
		temp = z__[j4 + 2] / z__[j4 - 3];
		d__ = d__ * temp - *tau;
		*dmin__ = min(*dmin__,d__);
		z__[j4 - 1] = z__[j4] * temp;
/* Computing MIN */
		d__1 = z__[j4 - 1];
		emin = min(d__1,emin);
/* L20: */
	    }
	}

/*        Unroll last two steps. */

	*dnm2 = d__;
	*dmin2 = *dmin__;
	j4 = ((*n0 - 2) << 2) - *pp;
	j4p2 = j4 + (*pp << 1) - 1;
	z__[j4 - 2] = *dnm2 + z__[j4p2];
	z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
	*dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]) - *tau;
	*dmin__ = min(*dmin__,*dnm1);

	*dmin1 = *dmin__;
	j4 += 4;
	j4p2 = j4 + (*pp << 1) - 1;
	z__[j4 - 2] = *dnm1 + z__[j4p2];
	z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
	*dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]) - *tau;
	*dmin__ = min(*dmin__,*dn);

    } else {

/*        Code for non IEEE arithmetic. */

	if (*pp == 0) {
	    i__1 = (*n0 - 3) << 2;
	    for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
		z__[j4 - 2] = d__ + z__[j4 - 1];
		if (d__ < 0.) {
		    return 0;
		} else {
		    z__[j4] = z__[j4 + 1] * (z__[j4 - 1] / z__[j4 - 2]);
		    d__ = z__[j4 + 1] * (d__ / z__[j4 - 2]) - *tau;
		}
		*dmin__ = min(*dmin__,d__);
/* Computing MIN */
		d__1 = emin, d__2 = z__[j4];
		emin = min(d__1,d__2);
/* L30: */
	    }
	} else {
	    i__1 = (*n0 - 3) << 2;
	    for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
		z__[j4 - 3] = d__ + z__[j4];
		if (d__ < 0.) {
		    return 0;
		} else {
		    z__[j4 - 1] = z__[j4 + 2] * (z__[j4] / z__[j4 - 3]);
		    d__ = z__[j4 + 2] * (d__ / z__[j4 - 3]) - *tau;
		}
		*dmin__ = min(*dmin__,d__);
/* Computing MIN */
		d__1 = emin, d__2 = z__[j4 - 1];
		emin = min(d__1,d__2);
/* L40: */
	    }
	}

/*        Unroll last two steps. */

	*dnm2 = d__;
	*dmin2 = *dmin__;
	j4 = ((*n0 - 2) << 2) - *pp;
	j4p2 = j4 + (*pp << 1) - 1;
	z__[j4 - 2] = *dnm2 + z__[j4p2];
	if (*dnm2 < 0.) {
	    return 0;
	} else {
	    z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
	    *dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]) - *tau;
	}
	*dmin__ = min(*dmin__,*dnm1);

	*dmin1 = *dmin__;
	j4 += 4;
	j4p2 = j4 + (*pp << 1) - 1;
	z__[j4 - 2] = *dnm1 + z__[j4p2];
	if (*dnm1 < 0.) {
	    return 0;
	} else {
	    z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
	    *dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]) - *tau;
	}
	*dmin__ = min(*dmin__,*dn);

    }

    z__[j4 + 2] = *dn;
    z__[(*n0 << 2) - *pp] = emin;
    return 0;

/*     End of DLASQ5 */

} /* dlasq5_ */