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use super::log1pf;
/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
/// Inverse hyperbolic tangent (f32)
///
/// Calculates the inverse hyperbolic tangent of `x`.
/// Is defined as `log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2`.
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
pub fn atanhf(mut x: f32) -> f32 {
let mut u = x.to_bits();
let sign = (u >> 31) != 0;
/* |x| */
u &= 0x7fffffff;
x = f32::from_bits(u);
if u < 0x3f800000 - (1 << 23) {
if u < 0x3f800000 - (32 << 23) {
/* handle underflow */
if u < (1 << 23) {
force_eval!((x * x) as f32);
}
} else {
/* |x| < 0.5, up to 1.7ulp error */
x = 0.5 * log1pf(2.0 * x + 2.0 * x * x / (1.0 - x));
}
} else {
/* avoid overflow */
x = 0.5 * log1pf(2.0 * (x / (1.0 - x)));
}
if sign {
-x
} else {
x
}
}