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Diffstat (limited to 'nuttx/libc/math/lib_exp.c')
-rw-r--r-- | nuttx/libc/math/lib_exp.c | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/nuttx/libc/math/lib_exp.c b/nuttx/libc/math/lib_exp.c new file mode 100644 index 000000000..62494251d --- /dev/null +++ b/nuttx/libc/math/lib_exp.c @@ -0,0 +1,126 @@ +/************************************************************************ + * 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 |