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