/* mpfr_tanh -- hyperbolic tangent

Copyright 2001, 2002, 2003, 2004 Free Software Foundation.

This file is part of the MPFR Library.

The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.

The MPFR Library 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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the MPFR Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#include "mpfr-impl.h"

 /* The computation of cosh is done by
        tanh= [e^(x)^2-1]/[e^(x)^2+1]  */
int
mpfr_tanh (mpfr_ptr y, mpfr_srcptr xt , mp_rnd_t rnd_mode) 
{
    /****** Declaration ******/
    mpfr_t x;
    int inexact;
    
    /* Special value checking */
    if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(xt)))
      {
	if (MPFR_IS_NAN(xt)) 
	  {
	    MPFR_SET_NAN(y); 
	    MPFR_RET_NAN;
	  }
	else if (MPFR_IS_INF(xt))
	  {
	    if (MPFR_IS_POS(xt))
	      return mpfr_set_ui (y, 1, rnd_mode); /* tanh(inf) = 1 */
	    else
	      return mpfr_set_si (y, -1, rnd_mode); /* tanh(-inf) = -1 */
	  }
	else /* tanh (0) = 0 and xt is zero */
	  {
            MPFR_ASSERTD (MPFR_IS_ZERO(xt));
	    MPFR_SET_ZERO (y);
	    MPFR_SET_SAME_SIGN (y, xt);
	    MPFR_RET (0);
	  }
      }

    mpfr_save_emin_emax ();
    MPFR_TMP_INIT_ABS (x, xt);

    /* General case */
    {
      /* Declaration of the intermediary variable */
      mpfr_t t, te;
      mp_exp_t d;

      /* Declaration of the size variable */
      mp_prec_t Nx = MPFR_PREC(x);   /* Precision of input variable */
      mp_prec_t Ny = MPFR_PREC(y);   /* Precision of output variable */
      mp_prec_t Nt;                  /* Precision of intermediary variables */
      long int err;                  /* Precision of error */
      
      /* Compute the precision of intermediary variable */
      Nt = MAX (Nx, Ny);
      /* The optimal number of bits: see algorithms.ps */
      Nt = Nt + /*__gmpfr_ceil_log2 (9)*/ 4 + __gmpfr_ceil_log2 (Nt);

      /* initialise of intermediary variable */
      mpfr_init2 (t, Nt); 
      mpfr_init2 (te, Nt);

      /* First computation of cosh */
      for (;;)
        {
          /* Compute tanh */
          mpfr_mul_2ui (te, x, 1, GMP_RNDN);  /* 2x */
          mpfr_exp (te, te, GMP_RNDN);        /* exp(2x) */
	  d = MPFR_GET_EXP (te);              /* For Error calculation */
          mpfr_add_ui (t, te, 1, GMP_RNDD);   /* exp(2x) + 1*/
          mpfr_sub_ui (te, te, 1, GMP_RNDU);  /* exp(2x) - 1*/
          mpfr_div (t, te, t, GMP_RNDN);      /* (exp(2x)-1)/(exp(2x)+1)*/

          /* Calculation of the error*/
          d = d - MPFR_GET_EXP (t);

          /* Estimation of the error */
          /*err = Nt-(__gmpfr_ceil_log2(7+pow(2,d+1)));*/
          err = Nt - (MAX(d + 1, 3) + 1);
	  
	  if (mpfr_can_round (t, err, GMP_RNDN, GMP_RNDZ,
			      Ny + (rnd_mode == GMP_RNDN)))
	    break;

          /* Actualisation of the precision */
          Nt += BITS_PER_MP_LIMB;
          mpfr_set_prec (t, Nt);
          mpfr_set_prec (te, Nt);
        }
 
      if (MPFR_IS_NEG (xt) )
        MPFR_CHANGE_SIGN(t);
      
      inexact = mpfr_set (y, t, rnd_mode);
      mpfr_clear (te);
      mpfr_clear (t);
    }
    mpfr_restore_emin_emax ();
    return mpfr_check_range (y, inexact, rnd_mode);
}