CMSIS_5/CMSIS/DSP/Source/FastMathFunctions/arm_atan2_f32.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_atan2_f32.c
 * Description:  float32 Arc tangent of y/x
 *
 * $Date:        22 April 2022
 * $Revision:    V1.10.0
 *
 * Target Processor: Cortex-M and Cortex-A cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2022 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "dsp/fast_math_functions.h"        

/*

atan for argument between in [0, 1.0]


*/

#define ATANHALFF32 0.463648f
#define PIHALFF32 1.5707963267948966192313f

#define ATAN2_NB_COEFS_F32 10

static const float32_t atan2_coefs_f32[ATAN2_NB_COEFS_F32]={0.0f
,1.0000001638308195518f
,-0.0000228941363602264f
,-0.3328086544578890873f
,-0.004404814619311061f
,0.2162217461808173258f
,-0.0207504842057097504f
,-0.1745263362250363339f
,0.1340557235283553386f
,-0.0323664125927477625f
};

__STATIC_FORCEINLINE float32_t arm_atan_limited_f32(float32_t x)
{
    float32_t res=atan2_coefs_f32[ATAN2_NB_COEFS_F32-1];
    int i=1;
    for(i=1;i<ATAN2_NB_COEFS_F32;i++)
    {
        res = x*res + atan2_coefs_f32[ATAN2_NB_COEFS_F32-1-i];
    }


    return(res);
}

__STATIC_FORCEINLINE float32_t arm_atan_f32(float32_t x)
{
   int sign=0;
   float32_t res=0.0f;

   if (x < 0.0f)
   {
      sign=1;
      x=-x;
   }

   if (x > 1.0f)
   {
      x = 1.0f / x;
      res = PIHALFF32 - arm_atan_limited_f32(x);
   }
   else
   {
     res += arm_atan_limited_f32(x);
   }


   if (sign)
   {
     res = -res;
   }

   return(res);
}


/**
  @ingroup groupFastMath
 */

/**
  @defgroup atan2 ArcTan2

  Computing Arc tangent only using the ratio y/x is not enough to determine the angle
  since there is an indeterminacy. Opposite quadrants are giving the same ratio.

  ArcTan2 is not using y/x to compute the angle but y and x and use the sign of y and x
  to determine the quadrant.

 */

/**
  @addtogroup atan2
  @{
 */

/**
  @brief       Arc Tangent of y/x using sign of y and x to get right quadrant
  @param[in]   y  y coordinate
  @param[in]   x  x coordinate
  @param[out]  result  Result
  @return  error status.
 
  @par         Compute the Arc tangent of y/x:
                   The sign of y and x are used to determine the right quadrant
                   and compute the right angle.
*/


arm_status arm_atan2_f32(float32_t y,float32_t x,float32_t *result)
{
    if (x > 0.0f)
    {
        *result=arm_atan_f32(y/x);
        return(ARM_MATH_SUCCESS);
    }
    if (x < 0.0f)
    {
        if (y > 0.0f)
        {
           *result=arm_atan_f32(y/x) + PI;
        }
        else if (y < 0.0f)
        {
           *result=arm_atan_f32(y/x) - PI;
        }
        else
        {
            if (signbit(y))
            {
               *result= -PI;
            }
            else
            {
               *result= PI;
            }
        }
        return(ARM_MATH_SUCCESS);
    }
    if (x == 0.0f)
    {
        if (y > 0.0f)
        {
            *result=PIHALFF32;
            return(ARM_MATH_SUCCESS);
        }
        if (y < 0.0f)
        {
            *result=-PIHALFF32;
            return(ARM_MATH_SUCCESS);
        }
    }
    

    return(ARM_MATH_NANINF);

}

/**
  @} end of atan2 group
 */