1 /* ---------------------------------------------------------------------- 2 * Project: CMSIS DSP Library 3 * Title: arm_linear_interp_q31.c 4 * Description: Q31 linear interpolation 5 * 6 * $Date: 23 April 2021 7 * $Revision: V1.9.0 8 * 9 * Target Processor: Cortex-M and Cortex-A cores 10 * -------------------------------------------------------------------- */ 11 /* 12 * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved. 13 * 14 * SPDX-License-Identifier: Apache-2.0 15 * 16 * Licensed under the Apache License, Version 2.0 (the License); you may 17 * not use this file except in compliance with the License. 18 * You may obtain a copy of the License at 19 * 20 * www.apache.org/licenses/LICENSE-2.0 21 * 22 * Unless required by applicable law or agreed to in writing, software 23 * distributed under the License is distributed on an AS IS BASIS, WITHOUT 24 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 25 * See the License for the specific language governing permissions and 26 * limitations under the License. 27 */ 28 29 #include "dsp/interpolation_functions.h" 30 31 /** 32 @ingroup groupInterpolation 33 */ 34 35 36 /** 37 * @addtogroup BilinearInterpolate 38 * @{ 39 */ 40 41 /** 42 * @brief Q31 bilinear interpolation. 43 * @param[in,out] S points to an instance of the interpolation structure. 44 * @param[in] X interpolation coordinate in 12.20 format. 45 * @param[in] Y interpolation coordinate in 12.20 format. 46 * @return out interpolated value. 47 */ arm_bilinear_interp_q31(arm_bilinear_interp_instance_q31 * S,q31_t X,q31_t Y)48 q31_t arm_bilinear_interp_q31( 49 arm_bilinear_interp_instance_q31 * S, 50 q31_t X, 51 q31_t Y) 52 { 53 q31_t out; /* Temporary output */ 54 q31_t acc = 0; /* output */ 55 q31_t xfract, yfract; /* X, Y fractional parts */ 56 q31_t x1, x2, y1, y2; /* Nearest output values */ 57 int32_t rI, cI; /* Row and column indices */ 58 q31_t *pYData = S->pData; /* pointer to output table values */ 59 uint32_t nCols = S->numCols; /* num of rows */ 60 61 /* Input is in 12.20 format */ 62 /* 12 bits for the table index */ 63 /* Index value calculation */ 64 rI = ((X & (q31_t)0xFFF00000) >> 20); 65 66 /* Input is in 12.20 format */ 67 /* 12 bits for the table index */ 68 /* Index value calculation */ 69 cI = ((Y & (q31_t)0xFFF00000) >> 20); 70 71 /* Care taken for table outside boundary */ 72 /* Returns zero output when values are outside table boundary */ 73 if (rI < 0 || rI > (S->numCols - 2) || cI < 0 || cI > (S->numRows - 2)) 74 { 75 return (0); 76 } 77 78 /* 20 bits for the fractional part */ 79 /* shift left xfract by 11 to keep 1.31 format */ 80 xfract = (X & 0x000FFFFF) << 11U; 81 82 /* Read two nearest output values from the index */ 83 x1 = pYData[(rI) + (int32_t)nCols * (cI) ]; 84 x2 = pYData[(rI) + (int32_t)nCols * (cI) + 1]; 85 86 /* 20 bits for the fractional part */ 87 /* shift left yfract by 11 to keep 1.31 format */ 88 yfract = (Y & 0x000FFFFF) << 11U; 89 90 /* Read two nearest output values from the index */ 91 y1 = pYData[(rI) + (int32_t)nCols * (cI + 1) ]; 92 y2 = pYData[(rI) + (int32_t)nCols * (cI + 1) + 1]; 93 94 /* Calculation of x1 * (1-xfract ) * (1-yfract) and acc is in 3.29(q29) format */ 95 out = ((q31_t) (((q63_t) x1 * (0x7FFFFFFF - xfract)) >> 32)); 96 acc = ((q31_t) (((q63_t) out * (0x7FFFFFFF - yfract)) >> 32)); 97 98 /* x2 * (xfract) * (1-yfract) in 3.29(q29) and adding to acc */ 99 out = ((q31_t) ((q63_t) x2 * (0x7FFFFFFF - yfract) >> 32)); 100 acc += ((q31_t) ((q63_t) out * (xfract) >> 32)); 101 102 /* y1 * (1 - xfract) * (yfract) in 3.29(q29) and adding to acc */ 103 out = ((q31_t) ((q63_t) y1 * (0x7FFFFFFF - xfract) >> 32)); 104 acc += ((q31_t) ((q63_t) out * (yfract) >> 32)); 105 106 /* y2 * (xfract) * (yfract) in 3.29(q29) and adding to acc */ 107 out = ((q31_t) ((q63_t) y2 * (xfract) >> 32)); 108 acc += ((q31_t) ((q63_t) out * (yfract) >> 32)); 109 110 /* Convert acc to 1.31(q31) format */ 111 return ((q31_t)(acc << 2)); 112 } 113 114 115 116 /** 117 * @} end of BilinearInterpolate group 118 */ 119 120
