1 files changed, 32 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/ilogb.rs b/library/compiler-builtins/libm/src/math/ilogb.rs
new file mode 100644
index 00000000000..5b41f7b1dc0
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/ilogb.rs
@@ -0,0 +1,32 @@
+const FP_ILOGBNAN: i32 = -1 - 0x7fffffff;
+const FP_ILOGB0: i32 = FP_ILOGBNAN;
+
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn ilogb(x: f64) -> i32 {
+    let mut i: u64 = x.to_bits();
+    let e = ((i >> 52) & 0x7ff) as i32;
+
+    if e == 0 {
+        i <<= 12;
+        if i == 0 {
+            force_eval!(0.0 / 0.0);
+            return FP_ILOGB0;
+        }
+        /* subnormal x */
+        let mut e = -0x3ff;
+        while (i >> 63) == 0 {
+            e -= 1;
+            i <<= 1;
+        }
+        e
+    } else if e == 0x7ff {
+        force_eval!(0.0 / 0.0);
+        if (i << 12) != 0 {
+            FP_ILOGBNAN
+        } else {
+            i32::MAX
+        }
+    } else {
+        e - 0x3ff
+    }
+}