function x = sqrt1(A)
% A>= 0, x>= 0
if A < 0 break;end
if A == 0
x = 0;
else
TwoPower = 1;
m = A;
while m >= 1, m = m/4; TwoPower = 2*TwoPower ; end
while m < .25, m = m*4; TwoPower = TwoPower/2; end
% sqrt(A) = sqrt(m)*TwoPower
x = (1+2*m)/3;
for k = 1:4
x = (x+ (m/x))/2;
end
x = x*TwoPower;
end