ref: 61870c24fae357b78029ce54be0c004e1ffdb3c7
dir: /libkern/sqrt.c/
/*
sqrt returns the square root of its floating
point argument. Newton's method.
calls frexp
*/
#include <lib9.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;
}