1 files changed, 26 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/acoshf.rs b/library/compiler-builtins/libm/src/math/acoshf.rs
new file mode 100644
index 00000000000..ad3455fdd48
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/acoshf.rs
@@ -0,0 +1,26 @@
+use super::{log1pf, logf, sqrtf};
+
+const LN2: f32 = 0.693147180559945309417232121458176568;
+
+/// Inverse hyperbolic cosine (f32)
+///
+/// Calculates the inverse hyperbolic cosine of `x`.
+/// Is defined as `log(x + sqrt(x*x-1))`.
+/// `x` must be a number greater than or equal to 1.
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn acoshf(x: f32) -> f32 {
+    let u = x.to_bits();
+    let a = u & 0x7fffffff;
+
+    if a < 0x3f800000 + (1 << 23) {
+        /* |x| < 2, invalid if x < 1 or nan */
+        /* up to 2ulp error in [1,1.125] */
+        return log1pf(x - 1.0 + sqrtf((x - 1.0) * (x - 1.0) + 2.0 * (x - 1.0)));
+    }
+    if a < 0x3f800000 + (12 << 23) {
+        /* |x| < 0x1p12 */
+        return logf(2.0 * x - 1.0 / (x + sqrtf(x * x - 1.0)));
+    }
+    /* x >= 0x1p12 */
+    return logf(x) + LN2;
+}