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122 lines
4.1 KiB
C
122 lines
4.1 KiB
C
/* ----------------------------------------------------------------------
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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 BilinearInterpolate
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* @{
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*/
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/**
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* @brief Q15 bilinear interpolation.
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* @param[in,out] S points to an instance of the interpolation structure.
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* @param[in] X interpolation coordinate in 12.20 format.
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* @param[in] Y interpolation coordinate in 12.20 format.
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* @return out interpolated value.
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*/
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q15_t arm_bilinear_interp_q15(
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arm_bilinear_interp_instance_q15 * S,
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q31_t X,
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q31_t Y)
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{
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q63_t acc = 0; /* output */
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q31_t out; /* Temporary output */
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q15_t x1, x2, y1, y2; /* Nearest output values */
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q31_t xfract, yfract; /* X, Y fractional parts */
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int32_t rI, cI; /* Row and column indices */
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q15_t *pYData = S->pData; /* pointer to output table values */
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uint32_t nCols = S->numCols; /* num of rows */
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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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rI = ((X & (q31_t)0xFFF00000) >> 20);
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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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cI = ((Y & (q31_t)0xFFF00000) >> 20);
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/* Care taken for table outside boundary */
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/* Returns zero output when values are outside table boundary */
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if (rI < 0 || rI > (S->numCols - 2) || cI < 0 || cI > (S->numRows - 2))
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{
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return (0);
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}
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/* 20 bits for the fractional part */
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/* xfract should be in 12.20 format */
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xfract = (X & 0x000FFFFF);
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/* Read two nearest output values from the index */
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x1 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI) ];
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x2 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI) + 1];
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/* 20 bits for the fractional part */
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/* yfract should be in 12.20 format */
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yfract = (Y & 0x000FFFFF);
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/* Read two nearest output values from the index */
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y1 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI + 1) ];
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y2 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI + 1) + 1];
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/* Calculation of x1 * (1-xfract ) * (1-yfract) and acc is in 13.51 format */
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/* x1 is in 1.15(q15), xfract in 12.20 format and out is in 13.35 format */
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/* convert 13.35 to 13.31 by right shifting and out is in 1.31 */
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out = (q31_t) (((q63_t) x1 * (0x0FFFFF - xfract)) >> 4U);
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acc = ((q63_t) out * (0x0FFFFF - yfract));
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/* x2 * (xfract) * (1-yfract) in 1.51 and adding to acc */
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out = (q31_t) (((q63_t) x2 * (0x0FFFFF - yfract)) >> 4U);
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acc += ((q63_t) out * (xfract));
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/* y1 * (1 - xfract) * (yfract) in 1.51 and adding to acc */
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out = (q31_t) (((q63_t) y1 * (0x0FFFFF - xfract)) >> 4U);
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acc += ((q63_t) out * (yfract));
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/* y2 * (xfract) * (yfract) in 1.51 and adding to acc */
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out = (q31_t) (((q63_t) y2 * (xfract)) >> 4U);
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acc += ((q63_t) out * (yfract));
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/* acc is in 13.51 format and down shift acc by 36 times */
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/* Convert out to 1.15 format */
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return ((q15_t)(acc >> 36));
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}
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/**
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* @} end of BilinearInterpolate group
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*/
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