text: /* ----------------------------------------------------------------------
   * Project:      CMSIS DSP Library
   * Title:        arm_cos_f32.c
   * Description:  Fast cosine calculation for floating-point values
   *
   * $Date:        27. January 2017
   * $Revision:    V.1.5.1
   *
   * Target Processor: Cortex-M cores
   * -------------------------------------------------------------------- */
  /*
   * Copyright (C) 2010-2017 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 "arm_math.h"
  #include "arm_common_tables.h"
  /**
   * @ingroup groupFastMath
   */
  
  /**
   * @defgroup cos Cosine
   *
   * Computes the trigonometric cosine function using a combination of table lookup
   * and linear interpolation.  There are separate functions for
   * Q15, Q31, and floating-point data types.
   * The input to the floating-point version is in radians while the
   * fixed-point Q15 and Q31 have a scaled input with the range
   * [0 +0.9999] mapping to [0 2*pi).  The fixed-point range is chosen so that a
   * value of 2*pi wraps around to 0.
   *
   * The implementation is based on table lookup using 256 values together with linear interpolation.
   * The steps used are:
   *  -# Calculation of the nearest integer table index
   *  -# Compute the fractional portion (fract) of the table index.
   *  -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
   *
   * where
   * <pre>
   *    b=Table[index+0];
   *    c=Table[index+1];
   * </pre>
   */
  
   /**
   * @addtogroup cos
   * @{
   */
  
  /**
   * @brief  Fast approximation to the trigonometric cosine function for floating-point data.
   * @param[in] x input value in radians.
   * @return cos(x).
   */
  
  float32_t arm_cos_f32(
    float32_t x)
  {
    float32_t cosVal, fract, in;                   /* Temporary variables for input, output */
    uint16_t index;                                /* Index variable */
    float32_t a, b;                                /* Two nearest output values */
    int32_t n;
    float32_t findex;
  
    /* input x is in radians */
    /* 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 */
    in = x * 0.159154943092f + 0.25f;
  
    /* Calculation of floor value of input */
    n = (int32_t) in;
  
    /* Make negative values towards -infinity */
    if (in < 0.0f)
    {
      n--;
    }
  
    /* Map input value to [0 1] */
    in = in - (float32_t) n;
  
    /* Calculation of index of the table */
    findex = (float32_t)FAST_MATH_TABLE_SIZE * in;
    index = (uint16_t)findex;
  
    /* when "in" is exactly 1, we need to rotate the index down to 0 */
    if (index >= FAST_MATH_TABLE_SIZE) {
      index = 0;
      findex -= (float32_t)FAST_MATH_TABLE_SIZE;
    }
  
    /* fractional value calculation */
    fract = findex - (float32_t) index;
  
    /* Read two nearest values of input value from the cos table */
    a = sinTable_f32[index];
    b = sinTable_f32[index+1];
  
    /* Linear interpolation process */
    cosVal = (1.0f-fract)*a + fract*b;
  
    /* Return the output value */
    return (cosVal);
  }
  
  /**
   * @} end of cos group
   */
  