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/* cosh.c
*
* Hyperbolic cosine
*
*
*
* SYNOPSIS:
*
* double x, y, cosh();
*
* y = cosh( x );
*
*
*
* DESCRIPTION:
*
* Returns hyperbolic cosine of argument in the range MINLOG to
* MAXLOG.
*
* cosh(x) = ( exp(x) + exp(-x) )/2.
*
*
*
* ACCURACY:
*
* Relative error:
* arithmetic domain # trials peak rms
* DEC +- 88 50000 4.0e-17 7.7e-18
* IEEE +-MAXLOG 30000 2.6e-16 5.7e-17
*
*
* ERROR MESSAGES:
*
* message condition value returned
* cosh overflow |x| > MAXLOG MAXNUM
*
*
*/
/* cosh.c */
/*
Cephes Math Library Release 2.8: June, 2000
Copyright 1985, 1995, 2000 by Stephen L. Moshier
*/
#include <math.h>
#ifdef ANSIPROT
extern double exp ( double );
extern int isnan ( double );
extern int isfinite ( double );
#else
double exp();
int isnan(), isfinite();
#endif
extern double MAXLOG, INFINITY, LOGE2;
double cosh(x)
double x;
{
double y;
#ifdef NANS
if( isnan(x) )
return(x);
#endif
if( x < 0 )
x = -x;
if( x > (MAXLOG + LOGE2) )
{
mtherr( "cosh", OVERFLOW );
return( INFINITY );
}
if( x >= (MAXLOG - LOGE2) )
{
y = exp(0.5 * x);
y = (0.5 * y) * y;
return(y);
}
y = exp(x);
y = 0.5 * (y + 1.0 / y);
return( y );
}
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