1 /* ---------------------------------------------------------------------- 2 * Project: CMSIS DSP Library 3 * Title: arm_linear_interp_q15.c 4 * Description: Q15 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 * @addtogroup BilinearInterpolate 37 * @{ 38 */ 39 40 /** 41 * @brief Q15 bilinear interpolation. 42 * @param[in,out] S points to an instance of the interpolation structure. 43 * @param[in] X interpolation coordinate in 12.20 format. 44 * @param[in] Y interpolation coordinate in 12.20 format. 45 * @return out interpolated value. 46 */ arm_bilinear_interp_q15(arm_bilinear_interp_instance_q15 * S,q31_t X,q31_t Y)47 q15_t arm_bilinear_interp_q15( 48 arm_bilinear_interp_instance_q15 * S, 49 q31_t X, 50 q31_t Y) 51 { 52 q63_t acc = 0; /* output */ 53 q31_t out; /* Temporary output */ 54 q15_t x1, x2, y1, y2; /* Nearest output values */ 55 q31_t xfract, yfract; /* X, Y fractional parts */ 56 int32_t rI, cI; /* Row and column indices */ 57 q15_t *pYData = S->pData; /* pointer to output table values */ 58 uint32_t nCols = S->numCols; /* num of rows */ 59 60 /* Input is in 12.20 format */ 61 /* 12 bits for the table index */ 62 /* Index value calculation */ 63 rI = ((X & (q31_t)0xFFF00000) >> 20); 64 65 /* Input is in 12.20 format */ 66 /* 12 bits for the table index */ 67 /* Index value calculation */ 68 cI = ((Y & (q31_t)0xFFF00000) >> 20); 69 70 /* Care taken for table outside boundary */ 71 /* Returns zero output when values are outside table boundary */ 72 if (rI < 0 || rI > (S->numCols - 2) || cI < 0 || cI > (S->numRows - 2)) 73 { 74 return (0); 75 } 76 77 /* 20 bits for the fractional part */ 78 /* xfract should be in 12.20 format */ 79 xfract = (X & 0x000FFFFF); 80 81 /* Read two nearest output values from the index */ 82 x1 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI) ]; 83 x2 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI) + 1]; 84 85 /* 20 bits for the fractional part */ 86 /* yfract should be in 12.20 format */ 87 yfract = (Y & 0x000FFFFF); 88 89 /* Read two nearest output values from the index */ 90 y1 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI + 1) ]; 91 y2 = pYData[((uint32_t)rI) + nCols * ((uint32_t)cI + 1) + 1]; 92 93 /* Calculation of x1 * (1-xfract ) * (1-yfract) and acc is in 13.51 format */ 94 95 /* x1 is in 1.15(q15), xfract in 12.20 format and out is in 13.35 format */ 96 /* convert 13.35 to 13.31 by right shifting and out is in 1.31 */ 97 out = (q31_t) (((q63_t) x1 * (0x0FFFFF - xfract)) >> 4U); 98 acc = ((q63_t) out * (0x0FFFFF - yfract)); 99 100 /* x2 * (xfract) * (1-yfract) in 1.51 and adding to acc */ 101 out = (q31_t) (((q63_t) x2 * (0x0FFFFF - yfract)) >> 4U); 102 acc += ((q63_t) out * (xfract)); 103 104 /* y1 * (1 - xfract) * (yfract) in 1.51 and adding to acc */ 105 out = (q31_t) (((q63_t) y1 * (0x0FFFFF - xfract)) >> 4U); 106 acc += ((q63_t) out * (yfract)); 107 108 /* y2 * (xfract) * (yfract) in 1.51 and adding to acc */ 109 out = (q31_t) (((q63_t) y2 * (xfract)) >> 4U); 110 acc += ((q63_t) out * (yfract)); 111 112 /* acc is in 13.51 format and down shift acc by 36 times */ 113 /* Convert out to 1.15 format */ 114 return ((q15_t)(acc >> 36)); 115 } 116 117 118 /** 119 * @} end of BilinearInterpolate group 120 */ 121 122
