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 LinearInterpolate 37 * @{ 38 */ 39 40 /** 41 * 42 * @brief Process function for the Q15 Linear Interpolation Function. 43 * @param[in] pYData pointer to Q15 Linear Interpolation table 44 * @param[in] x input sample to process 45 * @param[in] nValues number of table values 46 * @return y processed output sample. 47 * 48 * \par 49 * Input sample <code>x</code> is in 12.20 format which contains 12 bits for table index and 20 bits for fractional part. 50 * This function can support maximum of table size 2^12. 51 * 52 */ arm_linear_interp_q15(q15_t * pYData,q31_t x,uint32_t nValues)53 q15_t arm_linear_interp_q15( 54 q15_t * pYData, 55 q31_t x, 56 uint32_t nValues) 57 { 58 q63_t y; /* output */ 59 q15_t y0, y1; /* Nearest output values */ 60 q31_t fract; /* fractional part */ 61 int32_t index; /* Index to read nearest output values */ 62 63 /* Input is in 12.20 format */ 64 /* 12 bits for the table index */ 65 /* Index value calculation */ 66 index = ((x & (int32_t)0xFFF00000) >> 20); 67 68 if (index >= (int32_t)(nValues - 1)) 69 { 70 return (pYData[nValues - 1]); 71 } 72 else if (index < 0) 73 { 74 return (pYData[0]); 75 } 76 else 77 { 78 /* 20 bits for the fractional part */ 79 /* fract is in 12.20 format */ 80 fract = (x & 0x000FFFFF); 81 82 /* Read two nearest output values from the index */ 83 y0 = pYData[index]; 84 y1 = pYData[index + 1]; 85 86 /* Calculation of y0 * (1-fract) and y is in 13.35 format */ 87 y = ((q63_t) y0 * (0xFFFFF - fract)); 88 89 /* Calculation of (y0 * (1-fract) + y1 * fract) and y is in 13.35 format */ 90 y += ((q63_t) y1 * (fract)); 91 92 /* convert y to 1.15 format */ 93 return (q15_t) (y >> 20); 94 } 95 } 96 97 98 /** 99 * @} end of LinearInterpolate group 100 */ 101 102