102 lines
2.9 KiB
C
102 lines
2.9 KiB
C
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/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_linear_interp_q15.c
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* Description: Q15 linear interpolation
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*
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* $Date: 23 April 2021
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* $Revision: V1.9.0
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*
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* Target Processor: Cortex-M and Cortex-A cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2021 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 "dsp/interpolation_functions.h"
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/**
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@ingroup groupInterpolation
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*/
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/**
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* @addtogroup LinearInterpolate
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* @{
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*/
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/**
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*
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* @brief Process function for the Q15 Linear Interpolation Function.
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* @param[in] pYData pointer to Q15 Linear Interpolation table
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* @param[in] x input sample to process
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* @param[in] nValues number of table values
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* @return y processed output sample.
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*
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* \par
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* Input sample <code>x</code> is in 12.20 format which contains 12 bits for table index and 20 bits for fractional part.
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* This function can support maximum of table size 2^12.
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*
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*/
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q15_t arm_linear_interp_q15(
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const q15_t * pYData,
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q31_t x,
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uint32_t nValues)
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{
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q63_t y; /* output */
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q15_t y0, y1; /* Nearest output values */
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q31_t fract; /* fractional part */
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int32_t index; /* Index to read nearest output values */
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/* Input is in 12.20 format */
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/* 12 bits for the table index */
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/* Index value calculation */
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index = ((x & (int32_t)0xFFF00000) >> 20);
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if (index >= (int32_t)(nValues - 1))
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{
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return (pYData[nValues - 1]);
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}
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else if (index < 0)
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{
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return (pYData[0]);
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}
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else
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{
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/* 20 bits for the fractional part */
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/* fract is in 12.20 format */
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fract = (x & 0x000FFFFF);
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/* Read two nearest output values from the index */
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y0 = pYData[index];
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y1 = pYData[index + 1];
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/* Calculation of y0 * (1-fract) and y is in 13.35 format */
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y = ((q63_t) y0 * (0xFFFFF - fract));
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/* Calculation of (y0 * (1-fract) + y1 * fract) and y is in 13.35 format */
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y += ((q63_t) y1 * (fract));
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/* convert y to 1.15 format */
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return (q15_t) (y >> 20);
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}
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}
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/**
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* @} end of LinearInterpolate group
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*/
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