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/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 19. March 2015
* $Revision: V.1.4.5
*
* Project: CMSIS DSP Library
* Title: arm_cos_f32.c
*
* Description: Fast cosine calculation for floating-point 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
*/
/**
* @defgroup cos Cosine
*
* Computes the trigonometric cosine function using a combination of table lookup
* and cubic interpolation. There are separate functions for
* Q15, Q31, and floating-point data types.
* The input to the floating-point version is in radians while the
* fixed-point Q15 and Q31 have a scaled input with the range
* [0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
* value of 2*pi wraps around to 0.
*
* The implementation is based on table lookup using 256 values together with cubic interpolation.
* The steps used are:
* -# Calculation of the nearest integer table index
* -# Fetch the four table values a, b, c, and d
* -# Compute the fractional portion (fract) of the table index.
* -# Calculation of wa, wb, wc, wd
* -# The final result equals <code>a*wa + b*wb + c*wc + d*wd</code>
*
* where
* <pre>
* a=Table[index-1];
* b=Table[index+0];
* c=Table[index+1];
* d=Table[index+2];
* </pre>
* and
* <pre>
* wa=-(1/6)*fract.^3 + (1/2)*fract.^2 - (1/3)*fract;
* wb=(1/2)*fract.^3 - fract.^2 - (1/2)*fract + 1;
* wc=-(1/2)*fract.^3+(1/2)*fract.^2+fract;
* wd=(1/6)*fract.^3 - (1/6)*fract;
* </pre>
*/
/**
* @addtogroup cos
* @{
*/
/**
* @brief Fast approximation to the trigonometric cosine function for floating-point data.
* @param[in] x input value in radians.
* @return cos(x).
*/
float32_t arm_cos_f32(
float32_t x)
{
float32_t cosVal, fract, in; /* Temporary variables for input, output */
uint16_t index; /* Index variable */
float32_t a, b; /* Two nearest output values */
int32_t n;
float32_t findex;
/* input x is in radians */
/* Scale the input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25 (pi/2) to read sine table */
in = x * 0.159154943092f + 0.25f;
/* Calculation of floor value of input */
n = (int32_t) in;
/* Make negative values towards -infinity */
if(in < 0.0f)
{
n--;
}
/* Map input value to [0 1] */
in = in - (float32_t) n;
/* Calculation of index of the table */
findex = (float32_t) FAST_MATH_TABLE_SIZE * in;
index = ((uint16_t)findex) & 0x1ff;
/* fractional value calculation */
fract = findex - (float32_t) index;
/* Read two nearest values of input value from the cos table */
a = sinTable_f32[index];
b = sinTable_f32[index+1];
/* Linear interpolation process */
cosVal = (1.0f-fract)*a + fract*b;
/* Return the output value */
return (cosVal);
}
/**
* @} end of cos group
*/
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