LibrePilot/flight/libraries/math/sin_lookup.c

/**
 ******************************************************************************
 * @addtogroup OpenPilot Math Utilities
 * @{
 * @addtogroup Sine and cosine methods that use a cached lookup table
 * @{
 *
 * @file       sin_lookup.c
 * @author     The OpenPilot Team, http://www.openpilot.org Copyright (C) 2012.
 * @brief      Sine lookup table from flash with 1 degree resolution
 *
 * @see        The GNU Public License (GPL) Version 3
 *
 *****************************************************************************/
/*
 * 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 3 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, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include "openpilot.h"
#include "math.h"
#include "stdbool.h"
#include "stdint.h"
#include <pios_math.h>

#define FLASH_TABLE
#ifdef FLASH_TABLE
/** Version of the code which precomputes the lookup table in flash **/

// This is a precomputed sin lookup table over 90 degrees that
const float sin_table[] = {
    0.000000f, 0.017452f, 0.034899f, 0.052336f, 0.069756f, 0.087156f, 0.104528f, 0.121869f, 0.139173f, 0.156434f,
    0.173648f, 0.190809f, 0.207912f, 0.224951f, 0.241922f, 0.258819f, 0.275637f, 0.292372f, 0.309017f, 0.325568f,
    0.342020f, 0.358368f, 0.374607f, 0.390731f, 0.406737f, 0.422618f, 0.438371f, 0.453990f, 0.469472f, 0.484810f,
    0.500000f, 0.515038f, 0.529919f, 0.544639f, 0.559193f, 0.573576f, 0.587785f, 0.601815f, 0.615661f, 0.629320f,
    0.642788f, 0.656059f, 0.669131f, 0.681998f, 0.694658f, 0.707107f, 0.719340f, 0.731354f, 0.743145f, 0.754710f,
    0.766044f, 0.777146f, 0.788011f, 0.798636f, 0.809017f, 0.819152f, 0.829038f, 0.838671f, 0.848048f, 0.857167f,
    0.866025f, 0.874620f, 0.882948f, 0.891007f, 0.898794f, 0.906308f, 0.913545f, 0.920505f, 0.927184f, 0.933580f,
    0.939693f, 0.945519f, 0.951057f, 0.956305f, 0.961262f, 0.965926f, 0.970296f, 0.974370f, 0.978148f, 0.981627f,
    0.984808f, 0.987688f, 0.990268f, 0.992546f, 0.994522f, 0.996195f, 0.997564f, 0.998630f, 0.999391f, 0.999848f,
    1.000000f, 0.999848f, 0.999391f, 0.998630f, 0.997564f, 0.996195f, 0.994522f, 0.992546f, 0.990268f, 0.987688f,
    0.984808f, 0.981627f, 0.978148f, 0.974370f, 0.970296f, 0.965926f, 0.961262f, 0.956305f, 0.951057f, 0.945519f,
    0.939693f, 0.933580f, 0.927184f, 0.920505f, 0.913545f, 0.906308f, 0.898794f, 0.891007f, 0.882948f, 0.874620f,
    0.866025f, 0.857167f, 0.848048f, 0.838671f, 0.829038f, 0.819152f, 0.809017f, 0.798636f, 0.788011f, 0.777146f,
    0.766044f, 0.754710f, 0.743145f, 0.731354f, 0.719340f, 0.707107f, 0.694658f, 0.681998f, 0.669131f, 0.656059f,
    0.642788f, 0.629320f, 0.615661f, 0.601815f, 0.587785f, 0.573576f, 0.559193f, 0.544639f, 0.529919f, 0.515038f,
    0.500000f, 0.484810f, 0.469472f, 0.453990f, 0.438371f, 0.422618f, 0.406737f, 0.390731f, 0.374607f, 0.358368f,
    0.342020f, 0.325568f, 0.309017f, 0.292372f, 0.275637f, 0.258819f, 0.241922f, 0.224951f, 0.207912f, 0.190809f,
    0.173648f, 0.156434f, 0.139173f, 0.121869f, 0.104528f, 0.087156f, 0.069756f, 0.052336f, 0.034899f, 0.017452f
};

int sin_lookup_initalize()
{
    return 0;
}

#else /* ifdef FLASH_TABLE */
/** Version of the code which allocates the lookup table in heap **/

const int SIN_RESOLUTION = 180;

static float *sin_table;
int sin_lookup_initalize()
{
    // Previously initialized
    if (sin_table) {
        return 0;
    }

    sin_table = (float *)pvPortMalloc(sizeof(float) * SIN_RESOLUTION);
    if (sin_table == NULL) {
        return -1;
    }

    for (uint32_t i = 0; i < 180; i++) {
        sin_table[i] = sinf(DEG2RAD((float)i));
    }

    return 0;
}

#endif /* ifdef FLASH_TABLE */

/**
 * Use the lookup table to return sine(angle) where angle is in radians
 * to save flash this cheats and uses trig functions to only save
 * 90 values
 * @param[in] angle Angle in degrees
 * @returns sin(angle)
 */
float sin_lookup_deg(float angle)
{
    if (sin_table == NULL) {
        return 0;
    }

    // <bug, was> int i_ang = ((int32_t)angle) % 360;
    // 1073741760 is a multiple of 360 that is close to 0x3fffffff
    // so angle can be a very large number of positive or negative rotations
    // this is the fastest fix (no tests, one integer addition)
    // and has the largest range since float mantissas are 23-4 bit
    // we could halve the lookup table size
    // we could interpolate for greater accuracy
    int i_ang = ((int32_t)(angle + 0.5f) + (int32_t)1073741760) % 360;
    if (i_ang >= 180) { // for 180 to 360 deg
        return -sin_table[i_ang - 180];
    } else { // for 0 to 179 deg
        return sin_table[i_ang];
    }

    return 0;
}

/**
 * Get cos(angle) using the sine lookup table
 * @param[in] angle Angle in degrees
 * @returns cos(angle)
 */
float cos_lookup_deg(float angle)
{
    return sin_lookup_deg(angle + 90);
}

/**
 * Use the lookup table to return sine(angle) where angle is in radians
 * @param[in] angle Angle in radians
 * @returns sin(angle)
 */
float sin_lookup_rad(float angle)
{
    int degrees = RAD2DEG(angle);

    return sin_lookup_deg(degrees);
}

/**
 * Use the lookup table to return sine(angle) where angle is in radians
 * @param[in] angle Angle in radians
 * @returns cos(angle)
 */
float cos_lookup_rad(float angle)
{
    int degrees = RAD2DEG(angle);

    return cos_lookup_deg(degrees);
}