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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_cos_q15.c
* Description: Fast cosine calculation for Q15 values
*
* $Date: 18. March 2019
* $Revision: V1.6.0
*
* Target Processor: Cortex-M cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2019 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
*/
/**
@addtogroup cos
@{
*/
/**
@brief Fast approximation to the trigonometric cosine function for Q15 data.
@param[in] x Scaled input value in radians
@return cos(x)
The Q15 input value is in the range [0 +0.9999] and is mapped to a radian value in the range [0 2*PI).
*/
q15_t arm_cos_q15(
q15_t x)
{
q15_t cosVal; /* Temporary input, output variables */
int32_t index; /* Index variable */
q15_t a, b; /* Two nearest output values */
q15_t fract; /* Temporary values for fractional values */
/* add 0.25 (pi/2) to read sine table */
x = (uint16_t)x + 0x2000;
if (x < 0)
{ /* convert negative numbers to corresponding positive ones */
x = (uint16_t)x + 0x8000;
}
/* Calculate the nearest index */
index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
/* Calculation of fractional value */
fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
/* Read two nearest values of input value from the sin table */
a = sinTable_q15[index];
b = sinTable_q15[index+1];
/* Linear interpolation process */
cosVal = (q31_t) (0x8000 - fract) * a >> 16;
cosVal = (q15_t) ((((q31_t) cosVal << 16) + ((q31_t) fract * b)) >> 16);
/* Return output value */
return (cosVal << 1);
}
/**
@} end of cos group
*/
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