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/*
* This file is part of the UCB release of Plan 9. It is subject to the license
* terms in the LICENSE file found in the top-level directory of this
* distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
* part of the UCB release of Plan 9, including this file, may be copied,
* modified, propagated, or distributed except according to the terms contained
* in the LICENSE file.
*/
/*
sqrt returns the square root of its floating
point argument. Newton's method.
calls frexp
*/
#include <u.h>
#include <libc.h>
double
sqrt(double arg)
{
double x, temp;
int exp, i;
if(arg <= 0) {
if(arg < 0)
return NaN();
return 0;
}
if(isInf(arg, 1))
return arg;
x = frexp(arg, &exp);
while(x < 0.5) {
x *= 2;
exp--;
}
/*
* NOTE
* this wont work on 1's comp
*/
if(exp & 1) {
x *= 2;
exp--;
}
temp = 0.5 * (1.0+x);
while(exp > 60) {
temp *= (1L<<30);
exp -= 60;
}
while(exp < -60) {
temp /= (1L<<30);
exp += 60;
}
if(exp >= 0)
temp *= 1L << (exp/2);
else
temp /= 1L << (-exp/2);
for(i=0; i<=4; i++)
temp = 0.5*(temp + arg/temp);
return temp;
}