127 lines
3.4 KiB
C
127 lines
3.4 KiB
C
/************************************************************************
|
|
* libc/math/lib_exp.c
|
|
*
|
|
* This file is a part of NuttX:
|
|
*
|
|
* Copyright (C) 2012 Gregory Nutt. All rights reserved.
|
|
* Ported by: Darcy Gong
|
|
*
|
|
* It derives from the Rhombs OS math library by Nick Johnson which has
|
|
* a compatibile, MIT-style license:
|
|
*
|
|
* Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
|
|
*
|
|
* Permission to use, copy, modify, and distribute this software for any
|
|
* purpose with or without fee is hereby granted, provided that the above
|
|
* copyright notice and this permission notice appear in all copies.
|
|
*
|
|
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
|
|
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
|
|
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
|
|
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
|
|
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
|
|
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
|
|
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
|
|
*
|
|
************************************************************************/
|
|
|
|
/************************************************************************
|
|
* Included Files
|
|
************************************************************************/
|
|
|
|
#include <nuttx/config.h>
|
|
#include <nuttx/compiler.h>
|
|
|
|
#include <sys/types.h>
|
|
#include <math.h>
|
|
|
|
#include "lib_internal.h"
|
|
|
|
#ifdef CONFIG_HAVE_DOUBLE
|
|
|
|
/************************************************************************
|
|
* Private Data
|
|
************************************************************************/
|
|
|
|
static double _dbl_inv_fact[] =
|
|
{
|
|
1.0 / 1.0, /* 1 / 0! */
|
|
1.0 / 1.0, /* 1 / 1! */
|
|
1.0 / 2.0, /* 1 / 2! */
|
|
1.0 / 6.0, /* 1 / 3! */
|
|
1.0 / 24.0, /* 1 / 4! */
|
|
1.0 / 120.0, /* 1 / 5! */
|
|
1.0 / 720.0, /* 1 / 6! */
|
|
1.0 / 5040.0, /* 1 / 7! */
|
|
1.0 / 40320.0, /* 1 / 8! */
|
|
1.0 / 362880.0, /* 1 / 9! */
|
|
1.0 / 3628800.0, /* 1 / 10! */
|
|
1.0 / 39916800.0, /* 1 / 11! */
|
|
1.0 / 479001600.0, /* 1 / 12! */
|
|
1.0 / 6227020800.0, /* 1 / 13! */
|
|
1.0 / 87178291200.0, /* 1 / 14! */
|
|
1.0 / 1307674368000.0, /* 1 / 15! */
|
|
1.0 / 20922789888000.0, /* 1 / 16! */
|
|
1.0 / 355687428096000.0, /* 1 / 17! */
|
|
1.0 / 6402373705728000.0, /* 1 / 18! */
|
|
};
|
|
|
|
/************************************************************************
|
|
* Public Functions
|
|
************************************************************************/
|
|
|
|
double exp(double x)
|
|
{
|
|
size_t int_part;
|
|
bool invert;
|
|
double value;
|
|
double x0;
|
|
size_t i;
|
|
|
|
if (x == 0)
|
|
{
|
|
return 1;
|
|
}
|
|
else if (x < 0)
|
|
{
|
|
invert = true;
|
|
x = -x;
|
|
}
|
|
else
|
|
{
|
|
invert = false;
|
|
}
|
|
|
|
/* Extract integer component */
|
|
|
|
int_part = (size_t) x;
|
|
|
|
/* Set x to fractional component */
|
|
|
|
x -= (double)int_part;
|
|
|
|
/* Perform Taylor series approximation with nineteen terms */
|
|
|
|
value = 0.0;
|
|
x0 = 1.0;
|
|
for (i = 0; i < 19; i++)
|
|
{
|
|
value += x0 * _dbl_inv_fact[i];
|
|
x0 *= x;
|
|
}
|
|
|
|
/* Multiply by exp of the integer component */
|
|
|
|
value *= lib_expi(int_part);
|
|
|
|
if (invert)
|
|
{
|
|
return (1.0 / value);
|
|
}
|
|
else
|
|
{
|
|
return value;
|
|
}
|
|
}
|
|
#endif
|