lib/main/CMSIS/DSP/Source/FastMathFunctions/arm_cos_q15.c

   1 /* ----------------------------------------------------------------------
   2  * Project:      CMSIS DSP Library
   3  * Title:        arm_cos_q15.c
   4  * Description:  Fast cosine calculation for Q15 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 /**
  33  * @ingroup groupFastMath
  34  */
  35
  36  /**
  37  * @addtogroup cos
  38  * @{
  39  */
  40
  41 /**
  42  * @brief Fast approximation to the trigonometric cosine function for Q15 data.
  43  * @param[in] x Scaled input value in radians.
  44  * @return  cos(x).
  45  *
  46  * The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
  47  * value in the range [0 2*pi).
  48  */
  49
  50 q15_t arm_cos_q15(
  51   q15_t x)
  52 {
  53   q15_t cosVal;                                  /* Temporary variables for input, output */
  54   int32_t index;                                 /* Index variables */
  55   q15_t a, b;                                    /* Four nearest output values */
  56   q15_t fract;                                   /* Temporary values for fractional values */
  57
  58   /* add 0.25 (pi/2) to read sine table */
  59   x = (uint16_t)x + 0x2000;
  60   if (x < 0)
  61   {   /* convert negative numbers to corresponding positive ones */
  62       x = (uint16_t)x + 0x8000;
  63   }
  64
  65   /* Calculate the nearest index */
  66   index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
  67
  68   /* Calculation of fractional value */
  69   fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
  70
  71   /* Read two nearest values of input value from the sin table */
  72   a = sinTable_q15[index];
  73   b = sinTable_q15[index+1];
  74
  75   /* Linear interpolation process */
  76   cosVal = (q31_t)(0x8000-fract)*a >> 16;
  77   cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16);
  78
  79   return cosVal << 1;
  80 }
  81
  82 /**
  83  * @} end of cos group
  84  */