| /* ---------------------------------------------------------------------- | |
| * Project: CMSIS DSP Library | |
| * Title: arm_cos_q15.c | |
| * Description: Fast cosine calculation for Q15 values | |
| * | |
| * $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 groupFastMath | |
| */ | |
| /** | |
| @addtogroup cos | |
| @{ | |
| */ | |
| /** | |
| @brief Fast approximation to the trigonometric cosine function for Q15 data. | |
| @param[in] x Scaled input value in radians | |
| @return cos(x) | |
| The Q15 input value is in the range [0 +0.9999] and is mapped to a radian value in the range [0 2*PI). | |
| */ | |
| q15_t arm_cos_q15( | |
| q15_t x) | |
| { | |
| q15_t cosVal; /* Temporary input, output variables */ | |
| int32_t index; /* Index variable */ | |
| q15_t a, b; /* Two nearest output values */ | |
| q15_t fract; /* Temporary values for fractional values */ | |
| /* add 0.25 (pi/2) to read sine table */ | |
| x = (uint16_t)x + 0x2000; | |
| if (x < 0) | |
| { /* convert negative numbers to corresponding positive ones */ | |
| x = (uint16_t)x + 0x8000; | |
| } | |
| /* Calculate the nearest index */ | |
| index = (uint32_t)x >> FAST_MATH_Q15_SHIFT; | |
| /* Calculation of fractional value */ | |
| fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9; | |
| /* Read two nearest values of input value from the sin table */ | |
| a = sinTable_q15[index]; | |
| b = sinTable_q15[index+1]; | |
| /* Linear interpolation process */ | |
| cosVal = (q31_t) (0x8000 - fract) * a >> 16; | |
| cosVal = (q15_t) ((((q31_t) cosVal << 16) + ((q31_t) fract * b)) >> 16); | |
| /* Return output value */ | |
| return (cosVal << 1); | |
| } | |
| /** | |
| @} end of cos group | |
| */ | |