forked from Archive/PX4-Autopilot
102 lines
2.5 KiB
C
102 lines
2.5 KiB
C
/************************************************************************
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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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