Trailing-Edge
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PDP-10 Archives
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SRI_NIC_PERM_FS_1_19910112
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kcc-5/lib/pml/dcosh.c
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/*
* +++ NAME +++
*
* DCOSH Double precision hyperbolic cosine
*
* +++ INDEX +++
*
* DCOSH
* machine independent routines
* math libraries
*
* +++ DESCRIPTION +++
*
* Returns double precision hyperbolic cosine of double precision
* floating point number.
*
* +++ USAGE +++
*
* double dcosh(x)
* double x;
*
* +++ REFERENCES +++
*
* Fortran IV plus user's guide, Digital Equipment Corp. pp B-4
*
* +++ RESTRICTIONS +++
*
* Inputs greater than LN(MAX_POS_DBLF) result in overflow.
* Inputs less than LN(MIN_POS_DBLF) result in underflow.
*
* For precision information refer to documentation of the
* floating point library routines called.
*
* +++ PROGRAMMER +++
*
* Fred Fish
* Goodyear Aerospace Corp, Arizona Div.
* (602) 932-7000 work
* (602) 894-6881 home
*
* +++ INTERNALS +++
*
* Computes hyperbolic cosine from:
*
* DCOSH(X) = 0.5 * (DEXP(X) + DEXP(-X))
*
* ---
*/
/*)LIBRARY
*/
#include <stdio.h>
#include "c:pmluse.h"
#include "pml.h"
double dcosh(x)
double x;
{
double dexp();
if (x > LN_MAXPOSDBL) {
pmlerr(DCOSH_OVERFLOW);
return (MAX_POS_DBLF);
} else if (x < LN_MINPOSDBL) {
pmlerr(DCOSH_UNDERFLOW);
return (MIN_POS_DBLF);
} else {
return (0.5 * (dexp(x) + dexp(-x)) );
}
}