1  /* ----------------------------------------------------------------------
  2   * Project:      CMSIS DSP Library
  3   * Title:        arm_atan2_q15.c
  4   * Description:  float32 Arc tangent of y/x
  5   *
  6   * $Date:        22 April 2022
  7   * $Revision:    V1.10.0
  8   *
  9   * Target Processor: Cortex-M and Cortex-A cores
 10   * -------------------------------------------------------------------- */
 11  /*
 12   * Copyright (C) 2010-2022 ARM Limited or its affiliates. All rights reserved.
 13   *
 14   * SPDX-License-Identifier: Apache-2.0
 15   *
 16   * Licensed under the Apache License, Version 2.0 (the License); you may
 17   * not use this file except in compliance with the License.
 18   * You may obtain a copy of the License at
 19   *
 20   * www.apache.org/licenses/LICENSE-2.0
 21   *
 22   * Unless required by applicable law or agreed to in writing, software
 23   * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 24   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 25   * See the License for the specific language governing permissions and
 26   * limitations under the License.
 27   */
 28  
 29  #include "dsp/fast_math_functions.h"        
 30  #include "dsp/utils.h"        
 31  
 32  /*
 33  
 34  atan for argument between in [0, 1.0]
 35  
 36  */
 37  
 38  
 39  /* Q2.13 */
 40  #define ATANHALFQ13 0xed6
 41  #define PIHALFQ13 0x3244
 42  #define PIQ13 0x6488
 43  
 44  #define ATAN2_NB_COEFS_Q15 10
 45  
 46  static const q15_t atan2_coefs_q15[ATAN2_NB_COEFS_Q15]={0x0000
 47  ,0x7fff
 48  ,0xffff
 49  ,0xd567
 50  ,0xff70
 51  ,0x1bad
 52  ,0xfd58
 53  ,0xe9a9
 54  ,0x1129
 55  ,0xfbdb
 56  };
 57  
 58  __STATIC_FORCEINLINE q15_t arm_atan_limited_q15(q15_t x)
 59  {
 60      q31_t res=(q31_t)atan2_coefs_q15[ATAN2_NB_COEFS_Q15-1];
 61      int i=1;
 62      for(i=1;i<ATAN2_NB_COEFS_Q15;i++)
 63      {
 64          res = ((q31_t) x * res) >> 15U;
 65          res = res + ((q31_t) atan2_coefs_q15[ATAN2_NB_COEFS_Q15-1-i]) ;
 66      }
 67  
 68      res = __SSAT(res>>2,16);
 69  
 70      
 71      return(res);
 72  }
 73  
 74  
 75  __STATIC_FORCEINLINE q15_t arm_atan_q15(q15_t y,q15_t x)
 76  {
 77     int sign=0;
 78     q15_t res=0;
 79  
 80     if (y<0)
 81     {
 82       arm_negate_q15(&y,&y,1);
 83       sign=1-sign;
 84     }
 85  
 86     if (x < 0)
 87     {
 88        sign=1 - sign;
 89        arm_negate_q15(&x,&x,1);
 90     }
 91  
 92     if (y > x)
 93     {
 94      q15_t ratio;
 95      int16_t shift;
 96  
 97      arm_divide_q15(x,y,&ratio,&shift);
 98  
 99      arm_shift_q15(&ratio,shift,&ratio,1);
100     
101      res = PIHALFQ13 - arm_atan_limited_q15(ratio);
102        
103     }
104     else
105     {
106      q15_t ratio;
107      int16_t shift;
108  
109      arm_divide_q15(y,x,&ratio,&shift);
110  
111      arm_shift_q15(&ratio,shift,&ratio,1);
112  
113      res = arm_atan_limited_q15(ratio);
114  
115     }
116  
117  
118     if (sign)
119     {
120       arm_negate_q15(&res,&res,1);
121     }
122  
123     return(res);
124  }
125  
126  
127  /**
128    @ingroup groupFastMath
129   */
130  
131  
132  /**
133    @addtogroup atan2
134    @{
135   */
136  
137  /**
138    @brief       Arc Tangent of y/x using sign of y and x to get right quadrant
139    @param[in]   y  y coordinate
140    @param[in]   x  x coordinate
141    @param[out]  result  Result in Q2.13
142    @return  error status.
143   
144    @par         Compute the Arc tangent of y/x:
145                     The sign of y and x are used to determine the right quadrant
146                     and compute the right angle.
147  */
148  
149  
150  arm_status arm_atan2_q15(q15_t y,q15_t x,q15_t *result)
151  {
152      if (x > 0)
153      {
154          *result=arm_atan_q15(y,x);
155          return(ARM_MATH_SUCCESS);
156      }
157      if (x < 0)
158      {
159          if (y > 0)
160          {
161             *result=arm_atan_q15(y,x) + PIQ13;
162          }
163          else if (y < 0)
164          {
165             *result=arm_atan_q15(y,x) - PIQ13;
166          }
167          else
168          {
169              if (y<0)
170              {
171                 *result= -PIQ13;
172              }
173              else
174              {
175                 *result= PIQ13;
176              }
177          }
178          return(ARM_MATH_SUCCESS);
179      }
180      if (x == 0)
181      {
182          if (y > 0)
183          {
184              *result=PIHALFQ13;
185              return(ARM_MATH_SUCCESS);
186          }
187          if (y < 0)
188          {
189              *result=-PIHALFQ13;
190              return(ARM_MATH_SUCCESS);
191          }
192      }
193      
194  
195      return(ARM_MATH_NANINF);
196  
197  }
198  
199  /**
200    @} end of atan2 group
201   */