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  1. /* ----------------------------------------------------------------------
  2.  * Project:      CMSIS DSP Library
  3.  * Title:        arm_cos_f32.c
  4.  * Description:  Fast cosine calculation for floating-point values
  5.  *
  6.  * $Date:        27. January 2017
  7.  * $Revision:    V.1.5.1
  8.  *
  9.  * Target Processor: Cortex-M cores
  10.  * -------------------------------------------------------------------- */
  11. /*
  12.  * Copyright (C) 2010-2017 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 "arm_math.h"
  30. #include "arm_common_tables.h"
  31. /**
  32.  * @ingroup groupFastMath
  33.  */
  34.  
  35. /**
  36.  * @defgroup cos Cosine
  37.  *
  38.  * Computes the trigonometric cosine function using a combination of table lookup
  39.  * and linear interpolation.  There are separate functions for
  40.  * Q15, Q31, and floating-point data types.
  41.  * The input to the floating-point version is in radians and in the range [0 2*pi) while the
  42.  * fixed-point Q15 and Q31 have a scaled input with the range
  43.  * [0 +0.9999] mapping to [0 2*pi).  The fixed-point range is chosen so that a
  44.  * value of 2*pi wraps around to 0.
  45.  *
  46.  * The implementation is based on table lookup using 256 values together with linear interpolation.
  47.  * The steps used are:
  48.  *  -# Calculation of the nearest integer table index
  49.  *  -# Compute the fractional portion (fract) of the table index.
  50.  *  -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
  51.  *
  52.  * where
  53.  * <pre>
  54.  *    b=Table[index+0];
  55.  *    c=Table[index+1];
  56.  * </pre>
  57.  */
  58.  
  59.  /**
  60.  * @addtogroup cos
  61.  * @{
  62.  */
  63.  
  64. /**
  65.  * @brief  Fast approximation to the trigonometric cosine function for floating-point data.
  66.  * @param[in] x input value in radians.
  67.  * @return cos(x).
  68.  */
  69.  
  70. float32_t arm_cos_f32(
  71.   float32_t x)
  72. {
  73.   float32_t cosVal, fract, in;                   /* Temporary variables for input, output */
  74.   uint16_t index;                                /* Index variable */
  75.   float32_t a, b;                                /* Two nearest output values */
  76.   int32_t n;
  77.   float32_t findex;
  78.  
  79.   /* input x is in radians */
  80.   /* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
  81.   in = x * 0.159154943092f + 0.25f;
  82.  
  83.   /* Calculation of floor value of input */
  84.   n = (int32_t) in;
  85.  
  86.   /* Make negative values towards -infinity */
  87.   if (in < 0.0f)
  88.   {
  89.     n--;
  90.   }
  91.  
  92.   /* Map input value to [0 1] */
  93.   in = in - (float32_t) n;
  94.  
  95.   /* Calculation of index of the table */
  96.   findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
  97.   index = ((uint16_t)findex) & 0x1ff;
  98.  
  99.   /* fractional value calculation */
  100.   fract = findex - (float32_t) index;
  101.  
  102.   /* Read two nearest values of input value from the cos table */
  103.   a = sinTable_f32[index];
  104.   b = sinTable_f32[index+1];
  105.  
  106.   /* Linear interpolation process */
  107.   cosVal = (1.0f-fract)*a + fract*b;
  108.  
  109.   /* Return the output value */
  110.   return (cosVal);
  111. }
  112.  
  113. /**
  114.  * @} end of cos group
  115.  */
  116.