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/* ----------------------------------------------------------------------
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 * Project:      CMSIS DSP Library
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 * Title:        arm_cos_q31.c
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 * Description:  Fast cosine calculation for Q31 values
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 *
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 * $Date:        27. January 2017
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 * $Revision:    V.1.5.1
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 *
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 * Target Processor: Cortex-M cores
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 * -------------------------------------------------------------------- */
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/*
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 * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
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 *
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 * SPDX-License-Identifier: Apache-2.0
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 *
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 * Licensed under the Apache License, Version 2.0 (the License); you may
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 * not use this file except in compliance with the License.
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 * You may obtain a copy of the License at
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 *
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 * www.apache.org/licenses/LICENSE-2.0
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 *
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 * Unless required by applicable law or agreed to in writing, software
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 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
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 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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 * See the License for the specific language governing permissions and
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 * limitations under the License.
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 */
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#include "arm_math.h"
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#include "arm_common_tables.h"
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/**
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 * @ingroup groupFastMath
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 */
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 /**
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 * @addtogroup cos
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 * @{
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 */
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/**
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 * @brief Fast approximation to the trigonometric cosine function for Q31 data.
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 * @param[in] x Scaled input value in radians.
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 * @return  cos(x).
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 *
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 * The Q31 input value is in the range [0 +0.9999] and is mapped to a radian
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 * value in the range [0 2*pi).
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 */
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q31_t arm_cos_q31(
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  q31_t x)
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{
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  q31_t cosVal;                                  /* Temporary variables for input, output */
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  int32_t index;                                 /* Index variables */
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  q31_t a, b;                                    /* Four nearest output values */
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  q31_t fract;                                   /* Temporary values for fractional values */
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  /* add 0.25 (pi/2) to read sine table */
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  x = (uint32_t)x + 0x20000000;
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  if (x < 0)
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  {   /* convert negative numbers to corresponding positive ones */
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      x = (uint32_t)x + 0x80000000;
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  }
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  /* Calculate the nearest index */
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  index = (uint32_t)x >> FAST_MATH_Q31_SHIFT;
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  /* Calculation of fractional value */
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  fract = (x - (index << FAST_MATH_Q31_SHIFT)) << 9;
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  /* Read two nearest values of input value from the sin table */
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  a = sinTable_q31[index];
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  b = sinTable_q31[index+1];
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  /* Linear interpolation process */
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  cosVal = (q63_t)(0x80000000-fract)*a >> 32;
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  cosVal = (q31_t)((((q63_t)cosVal << 32) + ((q63_t)fract*b)) >> 32);
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  return cosVal << 1;
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}
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/**
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 * @} end of cos group
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 */
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