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/* coshl.c
*
* Hyperbolic cosine, long double precision
*
*
*
* SYNOPSIS:
*
* long double x, y, coshl();
*
* y = coshl( x );
*
*
*
* DESCRIPTION:
*
* Returns hyperbolic cosine of argument in the range MINLOGL to
* MAXLOGL.
*
* cosh(x) = ( exp(x) + exp(-x) )/2.
*
*
*
* ACCURACY:
*
* Relative error:
* arithmetic domain # trials peak rms
* IEEE +-10000 30000 1.1e-19 2.8e-20
*
*
* ERROR MESSAGES:
*
* message condition value returned
* cosh overflow |x| > MAXLOGL+LOGE2L INFINITYL
*
*
*/
/*
Cephes Math Library Release 2.7: May, 1998
Copyright 1985, 1991, 1998 by Stephen L. Moshier
*/
#include <math.h>
extern long double MAXLOGL, MAXNUML, LOGE2L;
#ifdef ANSIPROT
extern long double expl ( long double );
extern int isnanl ( long double );
#else
long double expl(), isnanl();
#endif
#ifdef INFINITIES
extern long double INFINITYL;
#endif
#ifdef NANS
extern long double NANL;
#endif
long double coshl(x)
long double x;
{
long double y;
#ifdef NANS
if( isnanl(x) )
return(x);
#endif
if( x < 0 )
x = -x;
if( x > (MAXLOGL + LOGE2L) )
{
mtherr( "coshl", OVERFLOW );
#ifdef INFINITIES
return( INFINITYL );
#else
return( MAXNUML );
#endif
}
if( x >= (MAXLOGL - LOGE2L) )
{
y = expl(0.5L * x);
y = (0.5L * y) * y;
return(y);
}
y = expl(x);
y = 0.5L * (y + 1.0L / y);
return( y );
}
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