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