1 /* ---------------------------------------------------------------------- 2 * Project: CMSIS DSP Library 3 * Title: arm_linear_interp_q7.c 4 * Description: Q7 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 LinearInterpolate 38 * @{ 39 */ 40 41 /** 42 * 43 * @brief Process function for the Q7 Linear Interpolation Function. 44 * @param[in] pYData pointer to Q7 Linear Interpolation table 45 * @param[in] x input sample to process 46 * @param[in] nValues number of table values 47 * @return y processed output sample. 48 * 49 * \par 50 * Input sample <code>x</code> is in 12.20 format which contains 12 bits for table index and 20 bits for fractional part. 51 * This function can support maximum of table size 2^12. 52 */ arm_linear_interp_q7(q7_t * pYData,q31_t x,uint32_t nValues)53 q7_t arm_linear_interp_q7( 54 q7_t * pYData, 55 q31_t x, 56 uint32_t nValues) 57 { 58 q31_t y; /* output */ 59 q7_t y0, y1; /* Nearest output values */ 60 q31_t fract; /* fractional part */ 61 uint32_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 if (x < 0) 67 { 68 return (pYData[0]); 69 } 70 index = (x >> 20) & 0xfff; 71 72 if (index >= (nValues - 1)) 73 { 74 return (pYData[nValues - 1]); 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 and are in 1.7(q7) format */ 83 y0 = pYData[index]; 84 y1 = pYData[index + 1]; 85 86 /* Calculation of y0 * (1-fract ) and y is in 13.27(q27) format */ 87 y = ((y0 * (0xFFFFF - fract))); 88 89 /* Calculation of y1 * fract + y0 * (1-fract) and y is in 13.27(q27) format */ 90 y += (y1 * fract); 91 92 /* convert y to 1.7(q7) format */ 93 return (q7_t) (y >> 20); 94 } 95 } 96 /** 97 * @} end of LinearInterpolate group 98 */ 99 100