1 /* atanf.c: Computes arctan of 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 -0.4708325141E+0
28 #define P1 -0.5090958253E-1
29 #define Q0 0.1412500740E+1
30 #define Q1 0.1000000000E+1
32 #define P(g,f) ((P1*g+P0)*g*f)
33 #define Q(g) (Q1*g+Q0)
35 #define K1 0.2679491924 /* 2-sqrt(3) */
36 #define K2 0.7320508076 /* sqrt(3)-1 */
37 #define K3 1.7320508076 /* sqrt(3) */
40 #define myconst __code
45 float atanf(const float x) _FLOAT_FUNC_REENTRANT
49 static myconst float a[]={ 0.0, 0.5235987756, 1.5707963268, 1.0471975512 };
59 f=((K2*f-1.0)+f)/(K3+f);
60 // What it is actually wanted is this more accurate formula,
61 // but SDCC optimizes it and then it does not work:
62 // f=(((K2*f-0.5)-0.5)+f)/(K3+f);