Output of file : ETANH.C contained in archive : CEPHES22.ZIP
/* xtanh.c */
/* hyperbolic tangent check routine */
/* this subroutine is used by the exponential function routine */
/* by Stephen L. Moshier. */

void etanh( x, y )
unsigned short *x, *y;
{
unsigned short e[NE], r[NE], j[NE], xx[NE], m2[NE];
short i, n;
long lj;

emov( x, r );
r[NE-1] &= (unsigned short )0x7fff;
if( ecmp(r, eone) >= 0 )
{
/* tanh(x) = (exp(x) - exp(-x)) / (exp(x) + exp(-x))
* Note eexp() calls xtanh, but with an argument less than (1 + log 2)/2.
*/
eexp( r, e );
ediv( e, eone, r );
esub( r, e, xx );
eadd( r, e, j );
ediv( j, xx, y );
return;
}

emov( etwo, m2 );
eneg( m2 );

n = NBITS/8; /* Number of terms to do in the continued fraction */
lj = 2 * n + 1;
ltoe( &lj, j );

emov( j, e );
emul( x, x, xx );

/* continued fraction */
for( i=0; i {
ediv( e, xx, r );
eadd( m2, j, j );
eadd( r, j, e );
}

ediv( e, x, y );
}

### 3 Responses to “Category : C Source CodeArchive   : CEPHES22.ZIPFilename : ETANH.C”

1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/