pub fn atan(x: &DBig, precision: usize) -> OxiNumResult<DBig>Expand description
Compute atan(x) using dashu-float’s binary conversion and Taylor
approach internally. For |x| <= 0.5 we use the series directly;
for larger |x| <= 1 we use the half-angle formula; for |x| > 1 we
use the identity atan(x) = pi/2 - atan(1/x).