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/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 12. March 2014
* $Revision: V1.4.4
*
* Project: CMSIS DSP Library
* Title: arm_cos_q31.c
*
* Description: Fast cosine calculation for Q31 values.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* - Neither the name of ARM LIMITED nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */
#include "arm_math.h"
#include "arm_common_tables.h"
/**
* @ingroup groupFastMath
*/
/**
* @addtogroup cos
* @{
*/
/**
* @brief Fast approximation to the trigonometric cosine function for Q31 data.
* @param[in] x Scaled input value in radians.
* @return cos(x).
*
* The Q31 input value is in the range [0 +0.9999] and is mapped to a radian
* value in the range [0 2*pi).
*/
q31_t arm_cos_q31(
q31_t x)
{
q31_t cosVal; /* Temporary variables for input, output */
int32_t index; /* Index variables */
q31_t a, b; /* Four nearest output values */
q31_t fract; /* Temporary values for fractional values */
/* add 0.25 (pi/2) to read sine table */
x += 0x20000000;
if(x < 0)
{ /* convert negative numbers to corresponding positive ones */
x = x + 0x80000000;
}
/* Calculate the nearest index */
index = (uint32_t)x >> FAST_MATH_Q31_SHIFT;
/* Calculation of fractional value */
fract = (x - (index << FAST_MATH_Q31_SHIFT)) << 9;
/* Read two nearest values of input value from the sin table */
a = sinTable_q31[index];
b = sinTable_q31[index+1];
/* Linear interpolation process */
cosVal = (q63_t)(0x80000000-fract)*a >> 32;
cosVal = (q31_t)((((q63_t)cosVal << 32) + ((q63_t)fract*b)) >> 32);
return cosVal << 1;
}
/**
* @} end of cos group
*/
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