| /* ---------------------------------------------------------------------- | |
| * Project: CMSIS DSP Library | |
| * Title: arm_linear_interp_q15.c | |
| * Description: Q15 linear interpolation | |
| * | |
| * $Date: 23 April 2021 | |
| * $Revision: V1.9.0 | |
| * | |
| * Target Processor: Cortex-M and Cortex-A cores | |
| * -------------------------------------------------------------------- */ | |
| /* | |
| * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved. | |
| * | |
| * SPDX-License-Identifier: Apache-2.0 | |
| * | |
| * Licensed under the Apache License, Version 2.0 (the License); you may | |
| * not use this file except in compliance with the License. | |
| * You may obtain a copy of the License at | |
| * | |
| * www.apache.org/licenses/LICENSE-2.0 | |
| * | |
| * Unless required by applicable law or agreed to in writing, software | |
| * distributed under the License is distributed on an AS IS BASIS, WITHOUT | |
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| * See the License for the specific language governing permissions and | |
| * limitations under the License. | |
| */ | |
| /** | |
| @ingroup groupInterpolation | |
| */ | |
| /** | |
| * @addtogroup LinearInterpolate | |
| * @{ | |
| */ | |
| /** | |
| * | |
| * @brief Process function for the Q15 Linear Interpolation Function. | |
| * @param[in] pYData pointer to Q15 Linear Interpolation table | |
| * @param[in] x input sample to process | |
| * @param[in] nValues number of table values | |
| * @return y processed output sample. | |
| * | |
| * \par | |
| * Input sample <code>x</code> is in 12.20 format which contains 12 bits for table index and 20 bits for fractional part. | |
| * This function can support maximum of table size 2^12. | |
| * | |
| */ | |
| q15_t arm_linear_interp_q15( | |
| const q15_t * pYData, | |
| q31_t x, | |
| uint32_t nValues) | |
| { | |
| q63_t y; /* output */ | |
| q15_t y0, y1; /* Nearest output values */ | |
| q31_t fract; /* fractional part */ | |
| int32_t index; /* Index to read nearest output values */ | |
| /* Input is in 12.20 format */ | |
| /* 12 bits for the table index */ | |
| /* Index value calculation */ | |
| index = ((x & (int32_t)0xFFF00000) >> 20); | |
| if (index >= (int32_t)(nValues - 1)) | |
| { | |
| return (pYData[nValues - 1]); | |
| } | |
| else if (index < 0) | |
| { | |
| return (pYData[0]); | |
| } | |
| else | |
| { | |
| /* 20 bits for the fractional part */ | |
| /* fract is in 12.20 format */ | |
| fract = (x & 0x000FFFFF); | |
| /* Read two nearest output values from the index */ | |
| y0 = pYData[index]; | |
| y1 = pYData[index + 1]; | |
| /* Calculation of y0 * (1-fract) and y is in 13.35 format */ | |
| y = ((q63_t) y0 * (0xFFFFF - fract)); | |
| /* Calculation of (y0 * (1-fract) + y1 * fract) and y is in 13.35 format */ | |
| y += ((q63_t) y1 * (fract)); | |
| /* convert y to 1.15 format */ | |
| return (q15_t) (y >> 20); | |
| } | |
| } | |
| /** | |
| * @} end of LinearInterpolate group | |
| */ | |