lib/main/CMSIS/DSP/Source/FastMathFunctions/arm_cos_f32.c

   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  */