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/* mpfr_cosh -- hyperbolic cosine
Copyright 2001, 2002, 2004, 2005, 2006 Free Software Foundation, Inc.
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., 51 Franklin Place, Fifth Floor, Boston,
MA 02110-1301, USA. */
#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"
/* The computation of cosh is done by *
* cosh= 1/2[e^(x)+e^(-x)] */
int
mpfr_cosh (mpfr_ptr y, mpfr_srcptr xt , mp_rnd_t rnd_mode)
{
mpfr_t x;
int inexact;
MPFR_SAVE_EXPO_DECL (expo);
MPFR_LOG_FUNC (("x[%#R]=%R rnd=%d", xt, xt, rnd_mode),
("y[%#R]=%R inexact=%d", y, y, inexact));
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))
{
MPFR_SET_INF(y);
MPFR_SET_POS(y);
MPFR_RET(0);
}
else
{
MPFR_ASSERTD(MPFR_IS_ZERO(xt));
return mpfr_set_ui (y, 1, rnd_mode); /* cosh(0) = 1 */
}
}
MPFR_SAVE_EXPO_MARK (expo);
MPFR_TMP_INIT_ABS(x, xt);
/* General case */
{
/* Declaration of the intermediary variable */
mpfr_t t, te;
/* Declaration of the size variable */
mp_prec_t Ny = MPFR_PREC(y); /* Precision of output variable */
mp_prec_t Nt; /* Precision of the intermediary variable */
long int err; /* Precision of error */
MPFR_ZIV_DECL (loop);
MPFR_GROUP_DECL (group);
/* compute the precision of intermediary variable */
/* The optimal number of bits : see algorithms.tex */
Nt = Ny + 3 + MPFR_INT_CEIL_LOG2 (Ny);
/* initialise of intermediary variables */
MPFR_GROUP_INIT_2 (group, Nt, t, te);
/* First computation of cosh */
MPFR_ZIV_INIT (loop, Nt);
for (;;)
{
/* Compute cosh */
mpfr_clear_flags ();
mpfr_exp (te, x, GMP_RNDD); /* exp(x) */
/* exp can overflow (but not underflow since x>0) */
/* BUG/TODO/FIXME: exp can overflow but cosh may be representable! */
if (MPFR_UNLIKELY (mpfr_overflow_p ()))
{
inexact = mpfr_overflow (y, rnd_mode, MPFR_SIGN_POS);
MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, MPFR_FLAGS_OVERFLOW);
break;
}
mpfr_ui_div (t, 1, te, GMP_RNDU); /* 1/exp(x) */
mpfr_add (t, te, t, GMP_RNDU); /* exp(x) + 1/exp(x)*/
mpfr_div_2ui (t, t, 1, GMP_RNDN); /* 1/2(exp(x) + 1/exp(x))*/
/* Estimation of the error */
err = Nt - 3;
/* Check if we can round */
if (MPFR_LIKELY (MPFR_CAN_ROUND (t, err, Ny, rnd_mode)))
{
inexact = mpfr_set (y, t, rnd_mode);
break;
}
/* Actualisation of the precision */
MPFR_ZIV_NEXT (loop, Nt);
MPFR_GROUP_REPREC_2 (group, Nt, t, te);
}
MPFR_ZIV_FREE (loop);
MPFR_GROUP_CLEAR (group);
}
MPFR_SAVE_EXPO_FREE (expo);
inexact = mpfr_check_range (y, inexact, rnd_mode);
return inexact;
}
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