log1p
extern double log1p(double x);
return log1p(x-1 + sqrt((x-1)*(x-1)+2*(x-1)));
x = log1p(x + x*x/(sqrt(x*x+1)+1));
y = 0.5*log1p(2*y + 2*y*y/(1-y));
y = 0.5*log1p(2*(y/(1-y)));
return log1p(x);
return log1p(x);