| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_cos_q15.c |
| * Description: Fast cosine calculation for Q15 values |
| * |
| * $Date: 27. January 2017 |
| * $Revision: V.1.5.1 |
| * |
| * Target Processor: Cortex-M cores |
| * -------------------------------------------------------------------- */ |
| /* |
| * Copyright (C) 2010-2017 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. |
| */ |
| |
| #include "arm_math.h" |
| #include "arm_common_tables.h" |
| |
| /** |
| * @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 variables for input, output */ |
| int32_t index; /* Index variables */ |
| q15_t a, b; /* Four 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 cosVal << 1; |
| } |
| |
| /** |
| * @} end of cos group |
| */ |