diff options
Diffstat (limited to 'nuttx/libc/math/lib_logf.c')
-rw-r--r-- | nuttx/libc/math/lib_logf.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/nuttx/libc/math/lib_logf.c b/nuttx/libc/math/lib_logf.c new file mode 100644 index 000000000..3815fef84 --- /dev/null +++ b/nuttx/libc/math/lib_logf.c @@ -0,0 +1,77 @@ +/************************************************************************ + * libc/math/lib_logf.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, 2010 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 <math.h> +#include <float.h> + +/************************************************************************ + * Public Functions + ************************************************************************/ + +float logf(float x) +{ + float y, y_old, ey, epsilon; + + y = 0.0; + y_old = 1.0; + epsilon = FLT_EPSILON; + + while (y > y_old + epsilon || y < y_old - epsilon) + { + y_old = y; + ey = exp(y); + y -= (ey - x) / ey; + + if (y > 700.0) + { + y = 700.0; + } + + if (y < -700.0) + { + y = -700.0; + } + + epsilon = (fabs(y) > 1.0) ? fabs(y) * FLT_EPSILON : FLT_EPSILON; + } + + if (y == 700.0) + { + return INFINITY; + } + + if (y == -700.0) + { + return INFINITY; + } + + return y; +} |