/*

 *  Mathlib : A C Library of Special Functions

 *  Copyright (C) 1998 Ross Ihaka

 *  Copyright (C) 2000 The R Core Team

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; either version 2 of the License, or

 *  (at your option) any later version.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, a copy is available at

 *  https://www.R-project.org/Licenses/

 *

 *  DESCRIPTION

 *

 *    The quantile function of the exponential distribution.

 *

 */

#include "nmath.h"

#include "dpq.h"

double qexp(double p, double scale, int lower_tail, int log_p)

{

#ifdef IEEE_754

    if (ISNAN(p) || ISNAN(scale))

  return p + scale;

#endif

    if (scale < 0) ML_WARN_return_NAN;

    R_Q_P01_check(p);

    if (p == R_DT_0)

  return 0;

    return - scale * R_DT_Clog(p);

}