1 /* tanhf.c: Computes tanh(x) where x is a 32-bit float as outlined in [1].
3 Copyright (C) 2001, 2002 Jesus Calvino-Fraga, jesusc@ieee.org
5 This library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 This library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with this library; if not, write to the Free Software
17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
19 /* [1] William James Cody and W. M. Waite. _Software manual for the
20 elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */
22 /* Version 1.0 - Initial release */
27 #define P0 -0.8237728127E+0
28 #define P1 -0.3831010665E-2
29 #define Q0 0.2471319654E+1
30 #define Q1 0.1000000000E+1
33 #define K1 0.5493061443E+0
34 /* SBIG=[ln(2)+(t+1)*ln(B)]/2 */
37 #define P(g) ((P1*g+P0)*g)
38 #define Q(g) (Q1*g+Q0)
40 float tanhf(const float x) _FLOAT_FUNC_REENTRANT
48 r=0.5-1.0/(expf(f+f)+1.0);