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Diffstat (limited to 'nuttx/libc/math/lib_sqrt.c')
-rw-r--r-- | nuttx/libc/math/lib_sqrt.c | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/nuttx/libc/math/lib_sqrt.c b/nuttx/libc/math/lib_sqrt.c new file mode 100644 index 000000000..e8a1c42ea --- /dev/null +++ b/nuttx/libc/math/lib_sqrt.c @@ -0,0 +1,99 @@ +/************************************************************************ + * libc/math/lib_sqrt.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 <math.h> +#include <errno.h> + +#include "lib_internal.h" + +/************************************************************************ + * Public Functions + ************************************************************************/ + +#ifdef CONFIG_HAVE_DOUBLE +double sqrt(double x) +{ + long double y, y1; + + if (x < 0.0) + { + errno = EDOM; + return NAN; + } + + if (isnan(x)) + { + return NAN; + } + + if (isinf(x)) + { + return INFINITY; + } + + if (x == 0.0) + { + return 0.0; + } + + /* Guess square root (using bit manipulation) */ + + y = lib_sqrtapprox(x); + + /* Perform four iterations of approximation. This number (4) is + * definitely optimal + */ + + y = 0.5 * (y + x / y); + y = 0.5 * (y + x / y); + y = 0.5 * (y + x / y); + y = 0.5 * (y + x / y); + + /* If guess was terribe (out of range of float). Repeat approximation + * until convergence. + */ + + if (y * y < x - 1.0 || y * y > x + 1.0) + { + y1 = -1.0; + while (y != y1) + { + y1 = y; + y = 0.5 * (y + x / y); + } + } + + return y; +} +#endif |