77 lines
2.1 KiB
C
Executable File
77 lines
2.1 KiB
C
Executable File
/* atanf.c: Computes arctan of a 32-bit float as outlined in [1]
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Copyright (C) 2001, 2002 Jesus Calvino-Fraga, jesusc@ieee.org
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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/* [1] William James Cody and W. M. Waite. _Software manual for the
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elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */
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/* Version 1.0 - Initial release */
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#include "math.h"
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#include "errno.h"
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#define P0 -0.4708325141E+0
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#define P1 -0.5090958253E-1
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#define Q0 0.1412500740E+1
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#define Q1 0.1000000000E+1
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#define P(g,f) ((P1*g+P0)*g*f)
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#define Q(g) (Q1*g+Q0)
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#define K1 0.2679491924 /* 2-sqrt(3) */
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#define K2 0.7320508076 /* sqrt(3)-1 */
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#define K3 1.7320508076 /* sqrt(3) */
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#ifdef SDCC_mcs51
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#define myconst code
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#else
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#define myconst const
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#endif
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float atanf(const float x) _FLOAT_FUNC_REENTRANT
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{
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float f, r, g;
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int n=0;
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static myconst float a[]={ 0.0, 0.5235987756, 1.5707963268, 1.0471975512 };
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f=fabsf(x);
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if(f>1.0)
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{
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f=1.0/f;
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n=2;
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}
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if(f>K1)
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{
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f=((K2*f-1.0)+f)/(K3+f);
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// What it is actually wanted is this more accurate formula,
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// but SDCC optimizes it and then it does not work:
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// f=(((K2*f-0.5)-0.5)+f)/(K3+f);
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n++;
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}
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if(fabsf(f)<EPS) r=f;
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else
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{
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g=f*f;
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r=f+P(g,f)/Q(g);
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}
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if(n>1) r=-r;
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r+=a[n];
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if(x<0.0) r=-r;
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return r;
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}
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