72 lines
1.8 KiB
C++
72 lines
1.8 KiB
C++
/* Copyright (C) 2010 Wildfire Games.
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* This file is part of 0 A.D.
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*
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* 0 A.D. is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* 0 A.D. 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
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "precompiled.h"
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#include "Fixed.h"
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// Based on http://www.dspguru.com/dsp/tricks/fixed-point-atan2-with-self-normalization
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CFixed_23_8 atan2_approx(CFixed_23_8 y, CFixed_23_8 x)
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{
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CFixed_23_8 zero;
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// Special case to avoid division-by-zero
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if (x.IsZero() && y.IsZero())
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return zero;
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CFixed_23_8 c1;
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c1.SetInternalValue(201); // pi/4 << 8
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CFixed_23_8 c2;
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c2.SetInternalValue(603); // 3*pi/4 << 8
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CFixed_23_8 abs_y = y.Absolute();
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CFixed_23_8 angle;
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if (x >= zero)
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{
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CFixed_23_8 r = (x - abs_y) / (x + abs_y);
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angle = c1 - c1.Multiply(r);
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}
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else
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{
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CFixed_23_8 r = (x + abs_y) / (abs_y - x);
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angle = c2 - c1.Multiply(r);
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}
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if (y < zero)
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return -angle;
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else
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return angle;
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}
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template<>
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CFixed_23_8 CFixed_23_8::Pi()
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{
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return CFixed_23_8(804); // = pi * 256
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}
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void sincos_approx(CFixed_23_8 a, CFixed_23_8& sin_out, CFixed_23_8& cos_out)
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{
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// XXX: mustn't use floating-point here - need a fixed-point emulation
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// TODO: it's stupid doing sin/cos with 8-bit precision - we ought to have a CFixed_16_16 instead
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sin_out = CFixed_23_8::FromDouble(sin(a.ToDouble()));
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cos_out = CFixed_23_8::FromDouble(cos(a.ToDouble()));
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}
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