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/*
* The Mana World
* Copyright (C) 2009 The Mana World Development Team
*
* This file is part of The Mana World.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "utils/mathutils.h"
/* A very fast function to calculate the approximate inverse square root of a
* floating point value and a helper function that uses it for getting the
* normal squareroot. For an explanation of the inverse squareroot function
* read:
* http://www.math.purdue.edu/~clomont/Math/Papers/2003/InvSqrt.pdf
*
* Unfortunately the original creator of this function seems to be unknown.
*/
float fastInvSqrt(float x)
{
union { int i; float x; } tmp;
float xhalf = 0.5f * x;
tmp.x = x;
tmp.i = 0x5f375a86 - (tmp.i >> 1);
x = tmp.x;
x = x * (1.5f - xhalf * x * x);
return x;
}
float fastSqrt(float x)
{
return 1.0f / fastInvSqrt(x);
}
float weightedAverage(float n1, float n2, float w)
{
if (w < 0.0f)
return n1;
if (w > 1.0f)
return n2;
return (w * n2 + (1.0f - w) * n1) / 2.0f;
}
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