/* DE1: $Id: m_bams.c 2840 2006-02-17 03:32:34Z danij $
 * Copyright (C) 2003, 2004 Jaakko Keränen <jaakko.keranen@iki.fi>
 *
 * 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
 * (at your option) 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: http://www.opensource.org/
 */

/*
 * m_bams.c: Binary Angle Mathematics
 *
 * Trigonometric functions.
 */

// HEADER FILES ------------------------------------------------------------

#include "de_platform.h"
#include <math.h>
#include "m_bams.h"

// MACROS ------------------------------------------------------------------

#define BAMS_TABLE_ACCURACY_SHIFT   13
#define BAMS_TABLE_ACCURACY         (1 << BAMS_TABLE_ACCURACY_SHIFT)

// TYPES -------------------------------------------------------------------

// EXTERNAL FUNCTION PROTOTYPES --------------------------------------------

// PUBLIC FUNCTION PROTOTYPES ----------------------------------------------

// PRIVATE FUNCTION PROTOTYPES ---------------------------------------------

// EXTERNAL DATA DECLARATIONS ----------------------------------------------

// PUBLIC DATA DEFINITIONS -------------------------------------------------

// PRIVATE DATA DEFINITIONS ------------------------------------------------

static binangle_t atantable[BAMS_TABLE_ACCURACY];

// CODE --------------------------------------------------------------------

void bamsInit()                 // Fill in the tables.
{
    int     i;

    for(i = 0; i < BAMS_TABLE_ACCURACY; i++)
    {
        atantable[i] = RAD2BANG(atan(i / (float) BAMS_TABLE_ACCURACY));
    }
}

binangle_t bamsAtan2(int y, int x)
{
    binangle_t bang;
    INTEGER64 absy = y, absx = x;   // << TABLE_ACCURACY needs space.

    if(!x && !y)
        return BANG_0;          // Indeterminate.

    // Make sure the absolute values are absolute.
    if(absy < 0)
        absy = -absy;
    if(absx < 0)
        absx = -absx;

    // We'll first determine what the angle is in the first quadrant.
    // That's what the tables are for.
    if(!absy)
        bang = BANG_0;
    else if(absy == absx)
        bang = BANG_45;
    else if(!absx)
        bang = BANG_90;
    else
    {
        // The special cases didn't help. Use the tables.
        // absx and absy can't be zero here.
        if(absy > absx)
            bang =
                BANG_90 -
                atantable[(absx << BAMS_TABLE_ACCURACY_SHIFT) / absy];
        else
            bang = atantable[(absy << BAMS_TABLE_ACCURACY_SHIFT) / absx];
    }

    // Now we know the angle in the first quadrant. Let's look at the signs
    // and choose the right quadrant.
    if(x < 0)                   // Flip horizontally?
    {
        bang = BANG_180 - bang;
    }
    if(y < 0)                   // Flip vertically?
    {
        // At the moment bang must be smaller than 180.
        bang = BANG_180 + BANG_180 - bang;
    }
    // This is the final angle.
    return bang;
}