1 files changed, 36 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/asinh.rs b/library/compiler-builtins/libm/src/math/asinh.rs
new file mode 100644
index 00000000000..75d3c3ad462
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/asinh.rs
@@ -0,0 +1,36 @@
+use super::{log, log1p, sqrt};
+
+const LN2: f64 = 0.693147180559945309417232121458176568; /* 0x3fe62e42,  0xfefa39ef*/
+
+/* asinh(x) = sign(x)*log(|x|+sqrt(x*x+1)) ~= x - x^3/6 + o(x^5) */
+/// Inverse hyperbolic sine (f64)
+///
+/// Calculates the inverse hyperbolic sine of `x`.
+/// Is defined as `sgn(x)*log(|x|+sqrt(x*x+1))`.
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn asinh(mut x: f64) -> f64 {
+    let mut u = x.to_bits();
+    let e = ((u >> 52) as usize) & 0x7ff;
+    let sign = (u >> 63) != 0;
+
+    /* |x| */
+    u &= (!0) >> 1;
+    x = f64::from_bits(u);
+
+    if e >= 0x3ff + 26 {
+        /* |x| >= 0x1p26 or inf or nan */
+        x = log(x) + LN2;
+    } else if e >= 0x3ff + 1 {
+        /* |x| >= 2 */
+        x = log(2.0 * x + 1.0 / (sqrt(x * x + 1.0) + x));
+    } else if e >= 0x3ff - 26 {
+        /* |x| >= 0x1p-26, up to 1.6ulp error in [0.125,0.5] */
+        x = log1p(x + x * x / (sqrt(x * x + 1.0) + 1.0));
+    } else {
+        /* |x| < 0x1p-26, raise inexact if x != 0 */
+        let x1p120 = f64::from_bits(0x4770000000000000);
+        force_eval!(x + x1p120);
+    }
+
+    if sign { -x } else { x }
+}