px4-firmware/nuttx/libc/math/lib_sqrtl.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