71 lines
2.7 KiB
C
71 lines
2.7 KiB
C
/****************************************************************************
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* libc/math/lib_erff.c
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*
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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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* Public Functions
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****************************************************************************/
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float erff(float x)
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{
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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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char sign;
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float t;
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float a1, a2, a3, a4, a5, p;
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a1 = 0.254829592F;
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a2 = -0.284496736F;
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a3 = 1.421413741F;
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a4 = -1.453152027F;
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a5 = 1.061405429F;
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p = 0.3275911F;
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sign = (x >= 0 ? 1 : -1);
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t = 1.0F/(1.0F + p*x);
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return sign * (1.0F - (((((a5 * t + a4) * t) + a3) * t + a2) * t + a1) * t * expf(-x * x));
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}
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