84 lines
2.5 KiB
C
84 lines
2.5 KiB
C
/* ----------------------------------------------------------------------
|
|
* Project: CMSIS DSP Library
|
|
* Title: arm_cos_q15.c
|
|
* Description: Fast cosine calculation for Q15 values
|
|
*
|
|
* $Date: 18. March 2019
|
|
* $Revision: V1.6.0
|
|
*
|
|
* Target Processor: Cortex-M cores
|
|
* -------------------------------------------------------------------- */
|
|
/*
|
|
* Copyright (C) 2010-2019 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 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
|
|
*/
|