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101 lines
2.5 KiB
101 lines
2.5 KiB
/************************************************************************ |
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* libc/math/lib_sqrtl.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 <math.h> |
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#include <errno.h> |
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#include "lib_internal.h" |
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/************************************************************************ |
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* Public Functions |
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************************************************************************/ |
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#ifdef CONFIG_HAVE_LONG_DOUBLE |
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long double sqrtl(long double x) |
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{ |
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long double y, y1; |
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/* Filter out invalid/trivial inputs */ |
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if (x < 0.0) |
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{ |
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errno = EDOM; |
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return NAN; |
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} |
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if (isnan(x)) |
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{ |
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return NAN; |
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} |
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if (isinf(x)) |
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{ |
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return INFINITY; |
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} |
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if (x == 0.0) |
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{ |
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return 0.0; |
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} |
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/* Guess square root (using bit manipulation) */ |
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y = lib_sqrtapprox(x); |
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/* Perform four iterations of approximation. This number (4) is |
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* definitely optimal |
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*/ |
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y = 0.5 * (y + x / y); |
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y = 0.5 * (y + x / y); |
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y = 0.5 * (y + x / y); |
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y = 0.5 * (y + x / y); |
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/* If guess was terribe (out of range of float). Repeat approximation |
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* until convergence |
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*/ |
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if (y * y < x - 1.0 || y * y > x + 1.0) |
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{ |
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y1 = -1.0; |
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while (y != y1) |
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{ |
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y1 = y; |
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y = 0.5 * (y + x / y); |
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} |
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} |
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return y; |
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} |
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#endif
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