1 files changed, 33 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/atanhf.rs b/library/compiler-builtins/libm/src/math/atanhf.rs
new file mode 100644
index 00000000000..80ccec1f67f
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/atanhf.rs
@@ -0,0 +1,33 @@
+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);
+            }
+        } 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 }
+}