85 lines
2.4 KiB
C
85 lines
2.4 KiB
C
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/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_cos_q15.c
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* Description: Fast cosine calculation for Q15 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 Q15 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 Q15 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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q15_t arm_cos_q15(
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q15_t x)
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{
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q15_t cosVal; /* Temporary variables for input, output */
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int32_t index; /* Index variables */
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q15_t a, b; /* Four nearest output values */
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q15_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 = (uint16_t)x + 0x2000;
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if (x < 0)
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{ /* convert negative numbers to corresponding positive ones */
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x = (uint16_t)x + 0x8000;
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}
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/* Calculate the nearest index */
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index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
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/* Calculation of fractional value */
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fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
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/* Read two nearest values of input value from the sin table */
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a = sinTable_q15[index];
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b = sinTable_q15[index+1];
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/* Linear interpolation process */
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cosVal = (q31_t)(0x8000-fract)*a >> 16;
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cosVal = (q15_t)((((q31_t)cosVal << 16) + ((q31_t)fract*b)) >> 16);
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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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