113 lines
2.9 KiB
C
113 lines
2.9 KiB
C
/************************************************************************
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* lib/math/lib_expf.c
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*
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* This file is a part of NuttX:
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*
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* Copyright (C) 2012 Gregory Nutt. All rights reserved.
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* Ported by: Darcy Gong
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*
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* It derives from the Rhombs OS math library by Nick Johnson which has
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* a compatibile, MIT-style license:
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*
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* Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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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 <sys/types.h>
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#include <math.h>
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#include "lib_internal.h"
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/************************************************************************
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* Private Data
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************************************************************************/
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static float _flt_inv_fact[] =
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{
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1.0 / 1.0, // 1/0!
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1.0 / 1.0, // 1/1!
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1.0 / 2.0, // 1/2!
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1.0 / 6.0, // 1/3!
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1.0 / 24.0, // 1/4!
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1.0 / 120.0, // 1/5!
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1.0 / 720.0, // 1/6!
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1.0 / 5040.0, // 1/7!
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1.0 / 40320.0, // 1/8!
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1.0 / 362880.0, // 1/9!
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1.0 / 3628800.0, // 1/10!
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};
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/************************************************************************
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* Public Functions
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************************************************************************/
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float expf(float x)
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{
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size_t int_part;
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bool invert;
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float value;
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float x0;
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size_t i;
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if (x == 0)
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{
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return 1;
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}
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else if (x < 0)
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{
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invert = true;
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x = -x;
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}
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else
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{
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invert = false;
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}
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/* Extract integer component */
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int_part = (size_t) x;
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/* set x to fractional component */
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x -= (float)int_part;
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/* Perform Taylor series approximation with eleven terms */
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value = 0.0;
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x0 = 1.0;
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for (i = 0; i < 10; i++)
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{
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value += x0 * _flt_inv_fact[i];
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x0 *= x;
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}
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/* Multiply by exp of the integer component */
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value *= lib_expi(int_part);
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if (invert)
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{
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return (1.0 / value);
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}
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else
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{
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return value;
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}
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}
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