1 /* $OpenBSD: etanh.c,v 1.1 2011/07/02 18:11:01 martynas Exp $ */ 2 3 /* 4 * Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net> 5 * 6 * Permission to use, copy, modify, and distribute this software for any 7 * purpose with or without fee is hereby granted, provided that the above 8 * copyright notice and this permission notice appear in all copies. 9 * 10 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17 */ 18 19 /* xtanh.c */ 20 /* hyperbolic tangent check routine */ 21 /* this subroutine is used by the exponential function routine */ 22 /* by Stephen L. Moshier. */ 23 24 25 26 #include "ehead.h" 27 28 29 void etanh( x, y ) 30 unsigned short *x, *y; 31 { 32 unsigned short e[NE], r[NE], j[NE], xx[NE], m2[NE]; 33 short i, n; 34 long lj; 35 36 emov( x, r ); 37 r[NE-1] &= (unsigned short )0x7fff; 38 if( ecmp(r, eone) >= 0 ) 39 { 40 /* tanh(x) = (exp(x) - exp(-x)) / (exp(x) + exp(-x)) 41 * Note eexp() calls xtanh, but with an argument less than (1 + log 2)/2. 42 */ 43 eexp( r, e ); 44 ediv( e, eone, r ); 45 esub( r, e, xx ); 46 eadd( r, e, j ); 47 ediv( j, xx, y ); 48 return; 49 } 50 51 emov( etwo, m2 ); 52 eneg( m2 ); 53 54 n = NBITS/8; /* Number of terms to do in the continued fraction */ 55 lj = 2 * n + 1; 56 ltoe( &lj, j ); 57 58 emov( j, e ); 59 emul( x, x, xx ); 60 61 /* continued fraction */ 62 for( i=0; i<n; i++) 63 { 64 ediv( e, xx, r ); 65 eadd( m2, j, j ); 66 eadd( r, j, e ); 67 } 68 69 ediv( e, x, y ); 70 } 71