169 lines
5.5 KiB
C
169 lines
5.5 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_bilinear_interp_f16.c
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* Description: Floating-point bilinear 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_f16.h"
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#if defined(ARM_FLOAT16_SUPPORTED)
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/**
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@ingroup groupInterpolation
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*/
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/**
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* @defgroup BilinearInterpolate Bilinear Interpolation
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*
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* Bilinear interpolation is an extension of linear interpolation applied to a two dimensional grid.
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* The underlying function <code>f(x, y)</code> is sampled on a regular grid and the interpolation process
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* determines values between the grid points.
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* Bilinear interpolation is equivalent to two step linear interpolation, first in the x-dimension and then in the y-dimension.
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* Bilinear interpolation is often used in image processing to rescale images.
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* The CMSIS DSP library provides bilinear interpolation functions for Q7, Q15, Q31, and floating-point data types.
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*
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* <b>Algorithm</b>
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* \par
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* The instance structure used by the bilinear interpolation functions describes a two dimensional data table.
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* For floating-point, the instance structure is defined as:
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* <pre>
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* typedef struct
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* {
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* uint16_t numRows;
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* uint16_t numCols;
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* float16_t *pData;
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* } arm_bilinear_interp_instance_f16;
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* </pre>
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*
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* \par
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* where <code>numRows</code> specifies the number of rows in the table;
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* <code>numCols</code> specifies the number of columns in the table;
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* and <code>pData</code> points to an array of size <code>numRows*numCols</code> values.
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* The data table <code>pTable</code> is organized in row order and the supplied data values fall on integer indexes.
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* That is, table element (x,y) is located at <code>pTable[x + y*numCols]</code> where x and y are integers.
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*
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* \par
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* Let <code>(x, y)</code> specify the desired interpolation point. Then define:
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* <pre>
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* XF = floor(x)
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* YF = floor(y)
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* </pre>
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* \par
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* The interpolated output point is computed as:
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* <pre>
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* f(x, y) = f(XF, YF) * (1-(x-XF)) * (1-(y-YF))
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* + f(XF+1, YF) * (x-XF)*(1-(y-YF))
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* + f(XF, YF+1) * (1-(x-XF))*(y-YF)
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* + f(XF+1, YF+1) * (x-XF)*(y-YF)
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* </pre>
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* Note that the coordinates (x, y) contain integer and fractional components.
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* The integer components specify which portion of the table to use while the
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* fractional components control the interpolation processor.
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*
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* \par
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* if (x,y) are outside of the table boundary, Bilinear interpolation returns zero output.
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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 Floating-point 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.
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* @param[in] Y interpolation coordinate.
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* @return out interpolated value.
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*/
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float16_t arm_bilinear_interp_f16(
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const arm_bilinear_interp_instance_f16 * S,
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float16_t X,
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float16_t Y)
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{
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float16_t out;
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float16_t f00, f01, f10, f11;
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float16_t *pData = S->pData;
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int32_t xIndex, yIndex, index;
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float16_t xdiff, ydiff;
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float16_t b1, b2, b3, b4;
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xIndex = (int32_t) X;
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yIndex = (int32_t) Y;
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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 (xIndex < 0 || xIndex > (S->numCols - 2) || yIndex < 0 || yIndex > (S->numRows - 2))
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{
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return (0);
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}
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/* Calculation of index for two nearest points in X-direction */
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index = (xIndex ) + (yIndex ) * S->numCols;
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/* Read two nearest points in X-direction */
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f00 = pData[index];
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f01 = pData[index + 1];
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/* Calculation of index for two nearest points in Y-direction */
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index = (xIndex ) + (yIndex+1) * S->numCols;
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/* Read two nearest points in Y-direction */
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f10 = pData[index];
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f11 = pData[index + 1];
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/* Calculation of intermediate values */
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b1 = f00;
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b2 = (_Float16)f01 - (_Float16)f00;
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b3 = (_Float16)f10 - (_Float16)f00;
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b4 = (_Float16)f00 - (_Float16)f01 - (_Float16)f10 + (_Float16)f11;
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/* Calculation of fractional part in X */
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xdiff = (_Float16)X - (_Float16)xIndex;
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/* Calculation of fractional part in Y */
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ydiff = (_Float16)Y - (_Float16)yIndex;
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/* Calculation of bi-linear interpolated output */
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out = (_Float16)b1 + (_Float16)b2 * (_Float16)xdiff +
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(_Float16)b3 * (_Float16)ydiff + (_Float16)b4 * (_Float16)xdiff * (_Float16)ydiff;
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/* return to application */
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return (out);
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}
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/**
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* @} end of BilinearInterpolate group
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*/
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#endif /* #if defined(ARM_FLOAT16_SUPPORTED) */
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