122 lines
3.4 KiB
C
122 lines
3.4 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_cos_f32.c
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* Description: Fast cosine calculation for floating-point values
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "arm_common_tables.h"
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#include "arm_math.h"
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/**
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@ingroup groupFastMath
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*/
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/**
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@defgroup cos Cosine
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Computes the trigonometric cosine function using a combination of table lookup
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and linear interpolation. There are separate functions for
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Q15, Q31, and floating-point data types.
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The input to the floating-point version is in radians while the
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fixed-point Q15 and Q31 have a scaled input with the range
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[0 +0.9999] mapping to [0 2*pi). The fixed-point range is chosen so that a
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value of 2*pi wraps around to 0.
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The implementation is based on table lookup using 256 values together with
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linear interpolation. The steps used are:
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-# Calculation of the nearest integer table index
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-# Compute the fractional portion (fract) of the table index.
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-# The final result equals <code>(1.0f-fract)*a + fract*b;</code>
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where
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<pre>
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b = Table[index];
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c = Table[index+1];
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</pre>
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*/
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/**
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@addtogroup cos
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@{
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*/
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/**
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@brief Fast approximation to the trigonometric cosine function for
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floating-point data.
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@param[in] x input value in radians
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@return cos(x)
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*/
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float32_t arm_cos_f32(float32_t x) {
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float32_t cosVal, fract, in; /* Temporary input, output variables */
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uint16_t index; /* Index variable */
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float32_t a, b; /* Two nearest output values */
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int32_t n;
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float32_t findex;
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/* input x is in radians */
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/* Scale input to [0 1] range from [0 2*PI] , divide input by 2*pi, add 0.25
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* (pi/2) to read sine table */
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in = x * 0.159154943092f + 0.25f;
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/* Calculation of floor value of input */
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n = (int32_t)in;
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/* Make negative values towards -infinity */
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if (in < 0.0f) {
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n--;
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}
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/* Map input value to [0 1] */
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in = in - (float32_t)n;
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/* Calculation of index of the table */
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findex = (float32_t)FAST_MATH_TABLE_SIZE * in;
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index = (uint16_t)findex;
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/* when "in" is exactly 1, we need to rotate the index down to 0 */
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if (index >= FAST_MATH_TABLE_SIZE) {
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index = 0;
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findex -= (float32_t)FAST_MATH_TABLE_SIZE;
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}
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/* fractional value calculation */
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fract = findex - (float32_t)index;
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/* Read two nearest values of input value from the cos table */
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a = sinTable_f32[index];
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b = sinTable_f32[index + 1];
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/* Linear interpolation process */
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cosVal = (1.0f - fract) * a + fract * b;
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/* Return output value */
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return (cosVal);
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}
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/**
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@} end of cos group
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*/
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