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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_linear_interp_f32.c
* Description: Floating-point 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
*/
/**
* @defgroup LinearInterpolate Linear Interpolation
*
* Linear interpolation is a method of curve fitting using linear polynomials.
* Linear interpolation works by effectively drawing a straight line between two neighboring samples and returning the appropriate point along that line
*
* \par
* \image html LinearInterp.gif "Linear interpolation"
*
* \par
* A Linear Interpolate function calculates an output value(y), for the input(x)
* using linear interpolation of the input values x0, x1( nearest input values) and the output values y0 and y1(nearest output values)
*
* \par Algorithm:
* <pre>
* y = y0 + (x - x0) * ((y1 - y0)/(x1-x0))
* where x0, x1 are nearest values of input x
* y0, y1 are nearest values to output y
* </pre>
*
* \par
* This set of functions implements Linear interpolation process
* for Q7, Q15, Q31, and floating-point data types. The functions operate on a single
* sample of data and each call to the function returns a single processed value.
* <code>S</code> points to an instance of the Linear Interpolate function data structure.
* <code>x</code> is the input sample value. The functions returns the output value.
*
* \par
* if x is outside of the table boundary, Linear interpolation returns first value of the table
* if x is below input range and returns last value of table if x is above range.
*/
/**
* @addtogroup LinearInterpolate
* @{
*/
/**
* @brief Process function for the floating-point Linear Interpolation Function.
* @param[in,out] S is an instance of the floating-point Linear Interpolation structure
* @param[in] x input sample to process
* @return y processed output sample.
*
*/
float32_t arm_linear_interp_f32(
arm_linear_interp_instance_f32 * S,
float32_t x)
{
float32_t y;
float32_t x0, x1; /* Nearest input values */
float32_t y0, y1; /* Nearest output values */
float32_t xSpacing = S->xSpacing; /* spacing between input values */
int32_t i; /* Index variable */
float32_t *pYData = S->pYData; /* pointer to output table */
/* Calculation of index */
i = (int32_t) ((x - S->x1) / xSpacing);
if (i < 0)
{
/* Iniatilize output for below specified range as least output value of table */
y = pYData[0];
}
else if ((uint32_t)i >= (S->nValues - 1))
{
/* Iniatilize output for above specified range as last output value of table */
y = pYData[S->nValues - 1];
}
else
{
/* Calculation of nearest input values */
x0 = S->x1 + i * xSpacing;
x1 = S->x1 + (i + 1) * xSpacing;
/* Read of nearest output values */
y0 = pYData[i];
y1 = pYData[i + 1];
/* Calculation of output */
y = y0 + (x - x0) * ((y1 - y0) / (x1 - x0));
}
/* returns output value */
return (y);
}
/**
* @} end of LinearInterpolate group
*/
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