1 files changed, 14 insertions, 0 deletions
diff --git a/vendor/compiler_builtins/libm/src/math/k_expo2.rs b/vendor/compiler_builtins/libm/src/math/k_expo2.rs
new file mode 100644
index 000000000..7345075f3
--- /dev/null
+++ b/vendor/compiler_builtins/libm/src/math/k_expo2.rs
@@ -0,0 +1,14 @@
+use super::exp;
+
+/* k is such that k*ln2 has minimal relative error and x - kln2 > log(FLT_MIN) */
+const K: i32 = 2043;
+
+/* expf(x)/2 for x >= log(FLT_MAX), slightly better than 0.5f*expf(x/2)*expf(x/2) */
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub(crate) fn k_expo2(x: f64) -> f64 {
+    let k_ln2 = f64::from_bits(0x40962066151add8b);
+    /* note that k is odd and scale*scale overflows */
+    let scale = f64::from_bits(((((0x3ff + K / 2) as u32) << 20) as u64) << 32);
+    /* exp(x - k ln2) * 2**(k-1) */
+    exp(x - k_ln2) * scale * scale
+}