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