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126 lines
3.4 KiB
126 lines
3.4 KiB
/************************************************************************ |
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* libc/math/lib_exp.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 <nuttx/config.h> |
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#include <nuttx/compiler.h> |
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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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#ifdef CONFIG_HAVE_DOUBLE |
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/************************************************************************ |
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* Private Data |
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************************************************************************/ |
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static double _dbl_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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1.0 / 39916800.0, // 1 / 11! |
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1.0 / 479001600.0, // 1 / 12! |
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1.0 / 6227020800.0, // 1 / 13! |
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1.0 / 87178291200.0, // 1 / 14! |
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1.0 / 1307674368000.0, // 1 / 15! |
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1.0 / 20922789888000.0, // 1 / 16! |
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1.0 / 355687428096000.0, // 1 / 17! |
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1.0 / 6402373705728000.0, // 1 / 18! |
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}; |
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/************************************************************************ |
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* Public Functions |
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************************************************************************/ |
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double exp(double x) |
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{ |
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size_t int_part; |
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bool invert; |
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double value; |
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double 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 -= (double)int_part; |
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/* Perform Taylor series approximation with nineteen terms */ |
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value = 0.0; |
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x0 = 1.0; |
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for (i = 0; i < 19; i++) |
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{ |
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value += x0 * _dbl_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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#endif
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