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CMSIS/DSP/Source/FastMathFunctions/arm_atan2_q15.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_atan2_q15.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"        
+#include "dsp/utils.h"        
+
+/*
+
+atan for argument between in [0, 1.0]
+
+*/
+
+
+/* Q2.13 */
+#define ATANHALFQ13 0xed6
+#define PIHALFQ13 0x3244
+#define PIQ13 0x6488
+
+#define ATAN2_NB_COEFS_Q15 10
+
+static const q15_t atan2_coefs_q15[ATAN2_NB_COEFS_Q15]={
+     0, // 0x0000
+ 32767, // 0x7fff
+    -1, // 0xffff
+-10905, // 0xd567
+  -144, // 0xff70
+  7085, // 0x1bad
+  -680, // 0xfd58
+ -5719, // 0xe9a9
+  4393, // 0x1129
+ -1061  // 0xfbdb
+};
+
+__STATIC_FORCEINLINE q15_t arm_atan_limited_q15(q15_t x)
+{
+    q31_t res=(q31_t)atan2_coefs_q15[ATAN2_NB_COEFS_Q15-1];
+    int i=1;
+    for(i=1;i<ATAN2_NB_COEFS_Q15;i++)
+    {
+        res = ((q31_t) x * res) >> 15U;
+        res = res + ((q31_t) atan2_coefs_q15[ATAN2_NB_COEFS_Q15-1-i]) ;
+    }
+
+    res = __SSAT(res>>2,16);
+
+    
+    return(res);
+}
+
+
+__STATIC_FORCEINLINE q15_t arm_atan_q15(q15_t y,q15_t x)
+{
+   int sign=0;
+   q15_t res=0;
+
+   if (y<0)
+   {
+     /* Negate y */
+#if defined (ARM_MATH_DSP)
+     y = __QSUB16(0, y);
+#else 
+     y = (y == (q15_t) 0x8000) ? (q15_t) 0x7fff : -y;
+#endif
+
+     sign=1-sign;
+   }
+
+   if (x < 0)
+   {
+      sign=1 - sign;
+     
+      /* Negate x */
+#if defined (ARM_MATH_DSP)
+     x = __QSUB16(0, x);
+#else 
+     x = (x == (q15_t) 0x8000) ? (q15_t) 0x7fff : -x;
+#endif
+   }
+
+   if (y > x)
+   {
+    q15_t ratio;
+    int16_t shift;
+
+    arm_divide_q15(x,y,&ratio,&shift);
+
+    /* Shift ratio by shift */
+    if (shift >=0)
+    {
+       ratio = __SSAT(((q31_t) ratio << shift), 16);
+    }
+    else
+    {
+       ratio = (ratio >> -shift);
+    }
+   
+    res = PIHALFQ13 - arm_atan_limited_q15(ratio);
+      
+   }
+   else
+   {
+    q15_t ratio;
+    int16_t shift;
+
+    arm_divide_q15(y,x,&ratio,&shift);
+
+    /* Shift ratio by shift */
+    if (shift >=0)
+    {
+       ratio = __SSAT(((q31_t) ratio << shift), 16);
+    }
+    else
+    {
+       ratio = (ratio >> -shift);
+    }
+   
+
+    res = arm_atan_limited_q15(ratio);
+
+   }
+
+
+   if (sign)
+   {
+     /* Negate res */
+#if defined (ARM_MATH_DSP)
+     res = __QSUB16(0, res);
+#else 
+     res = (res == (q15_t) 0x8000) ? (q15_t) 0x7fff : -res;
+#endif
+   }
+
+   return(res);
+}
+
+
+/**
+  @ingroup groupFastMath
+ */
+
+
+/**
+  @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 in Q2.13
+  @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_q15(q15_t y,q15_t x,q15_t *result)
+{
+    if (x > 0)
+    {
+        *result=arm_atan_q15(y,x);
+        return(ARM_MATH_SUCCESS);
+    }
+    if (x < 0)
+    {
+        if (y > 0)
+        {
+           *result=arm_atan_q15(y,x) + PIQ13;
+        }
+        else if (y < 0)
+        {
+           *result=arm_atan_q15(y,x) - PIQ13;
+        }
+        else
+        {
+            if (y<0)
+            {
+               *result= -PIQ13;
+            }
+            else
+            {
+               *result= PIQ13;
+            }
+        }
+        return(ARM_MATH_SUCCESS);
+    }
+    if (x == 0)
+    {
+        if (y > 0)
+        {
+            *result=PIHALFQ13;
+            return(ARM_MATH_SUCCESS);
+        }
+        if (y < 0)
+        {
+            *result=-PIHALFQ13;
+            return(ARM_MATH_SUCCESS);
+        }
+    }
+    
+
+    return(ARM_MATH_NANINF);
+
+}
+
+/**
+  @} end of atan2 group
+ */