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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_cos_q15.c
* Description: Fast cosine calculation for Q15 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
*/
/**
* @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 variables for input, output */
int32_t index; /* Index variables */
q15_t a, b; /* Four 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 cosVal << 1;
}
/**
* @} end of cos group
*/
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