82 lines
3.2 KiB
C
82 lines
3.2 KiB
C
/****************************************************************************
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* libs/libc/math/lib_erff.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Copyright (C) 2015 Brennan Ashton. All rights reserved.
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* Author: Brennan Ashton <bashton@brennanashton.com>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <nuttx/compiler.h>
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#include <math.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define A1 0.254829592F
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#define A2 (-0.284496736F)
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#define A3 1.421413741F
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#define A4 (-1.453152027F)
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#define A5 1.061405429F
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#define P 0.3275911F
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: erff
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*
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* Description:
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* This implementation comes from the Handbook of Mathmatical Functions
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* The implementations in this book are not protected by copyright.
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* erf comes from formula 7.1.26
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*
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****************************************************************************/
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float erff(float x)
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{
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float t;
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float z;
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z = fabsf(x);
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t = 1.0F / (1.0F + P * z);
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t = 1.0F -
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(((((A5 * t + A4) * t) + A3) * t + A2) * t + A1) * t * expf(-z * z);
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return copysignf(t, x);
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}
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