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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_cos_f32.c
* Description: Fast cosine calculation for floating-point 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
*/
/**
* @defgroup cos Cosine
*
* Computes the trigonometric cosine function using a combination of table lookup
* and linear interpolation. There are separate functions for
* Q15, Q31, and floating-point data types.
* The input to the floating-point version is in radians and in the range [0 2*pi) 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 linear interpolation.
* The steps used are:
* -# Calculation of the nearest integer table index
* -# Compute the fractional portion (fract) of the table index.
* -# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
*
* where
* <pre>
* b=Table[index+0];
* c=Table[index+1];
* </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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