mirror of
https://sourceware.org/git/glibc.git
synced 2025-11-03 20:53:13 +03:00
121 lines
2.6 KiB
C
121 lines
2.6 KiB
C
/*
|
|
* Copyright (c) 1985 Regents of the University of California.
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms are permitted provided
|
|
* that: (1) source distributions retain this entire copyright notice and
|
|
* comment, and (2) distributions including binaries display the following
|
|
* acknowledgement: ``This product includes software developed by the
|
|
* University of California, Berkeley and its contributors'' in the
|
|
* documentation or other materials provided with the distribution and in
|
|
* all advertising materials mentioning features or use of this software.
|
|
* Neither the name of the University nor the names of its contributors may
|
|
* be used to endorse or promote products derived from this software without
|
|
* specific prior written permission.
|
|
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
|
|
* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
|
|
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
|
|
*/
|
|
|
|
#include <ansidecl.h>
|
|
#include <errno.h>
|
|
#include <math.h>
|
|
|
|
/* Return the square root of X. */
|
|
double
|
|
DEFUN (sqrt, (x), double x)
|
|
{
|
|
double q, s, b, r, t;
|
|
CONST double zero = 0.0;
|
|
int m, n, i;
|
|
|
|
/* sqrt (NaN) is NaN; sqrt (+-0) is +-0. */
|
|
if (__isnan (x) || x == zero)
|
|
return x;
|
|
|
|
if (x < zero)
|
|
return zero / zero;
|
|
|
|
/* sqrt (Inf) is Inf. */
|
|
if (__isinf (x))
|
|
return x;
|
|
|
|
/* Scale X to [1,4). */
|
|
n = __logb (x);
|
|
x = __scalb (x, -n);
|
|
m = __logb (x);
|
|
if (m != 0)
|
|
/* Subnormal number. */
|
|
x = __scalb (x, -m);
|
|
|
|
m += n;
|
|
n = m / 2;
|
|
|
|
if ((n + n) != m)
|
|
{
|
|
x *= 2;
|
|
--m;
|
|
n = m / 2;
|
|
}
|
|
|
|
/* Generate sqrt (X) bit by bit (accumulating in Q). */
|
|
q = 1.0;
|
|
s = 4.0;
|
|
x -= 1.0;
|
|
r = 1;
|
|
for (i = 1; i <= 51; i++)
|
|
{
|
|
t = s + 1;
|
|
x *= 4;
|
|
r /= 2;
|
|
if (t <= x)
|
|
{
|
|
s = t + t + 2, x -= t;
|
|
q += r;
|
|
}
|
|
else
|
|
s *= 2;
|
|
}
|
|
|
|
/* Generate the last bit and determine the final rounding. */
|
|
r /= 2;
|
|
x *= 4;
|
|
if (x == zero)
|
|
goto end;
|
|
(void) (100 + r); /* Trigger inexact flag. */
|
|
if (s < x)
|
|
{
|
|
q += r;
|
|
x -= s;
|
|
s += 2;
|
|
s *= 2;
|
|
x *= 4;
|
|
t = (x - s) - 5;
|
|
b = 1.0 + 3 * r / 4;
|
|
if (b == 1.0)
|
|
goto end; /* B == 1: Round to zero. */
|
|
b = 1.0 + r / 4;
|
|
if (b > 1.0)
|
|
t = 1; /* B > 1: Round to +Inf. */
|
|
if (t >= 0)
|
|
q += r;
|
|
} /* Else round to nearest. */
|
|
else
|
|
{
|
|
s *= 2;
|
|
x *= 4;
|
|
t = (x - s) - 1;
|
|
b = 1.0 + 3 * r / 4;
|
|
if (b == 1.0)
|
|
goto end;
|
|
b = 1.0 + r / 4;
|
|
if (b > 1.0)
|
|
t = 1;
|
|
if (t >= 0)
|
|
q += r;
|
|
}
|
|
|
|
end:
|
|
return __scalb (q, n);
|
|
}
|