forked from Archive/PX4-Autopilot
102 lines
2.5 KiB
C
102 lines
2.5 KiB
C
|
/************************************************************************
|
||
|
|
* libc/math/lib_sqrtl.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_LONG_DOUBLE
|
||
|
|
long double sqrtl(long double x)
|
||
|
|
{
|
||
|
|
long double y, y1;
|
||
|
|
|
||
|
|
/* Filter out invalid/trivial inputs */
|
||
|
|
|
||
|
|
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
|