70 lines
2.4 KiB
C
70 lines
2.4 KiB
C
/****************************************************************************
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* libs/libc/math/lib_erf.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://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. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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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#ifdef CONFIG_HAVE_DOUBLE
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define A1 0.254829592
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#define A2 (-0.284496736)
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#define A3 1.421413741
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#define A4 (-1.453152027)
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#define A5 1.061405429
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#define P 0.3275911
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: erf
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*
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* Description:
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* This implementation comes from the Handbook of Mathematical 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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double erf(double x)
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{
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double t;
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double z;
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z = fabs(x);
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t = 1.0 / (1.0 + P * z);
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t = 1.0 -
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(((((A5 * t + A4) * t) + A3) * t + A2) * t + A1) * t * exp(-z * z);
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return copysign(t, x);
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}
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#endif /* CONFIG_HAVE_DOUBLE */
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