1 files changed, 30 insertions, 0 deletions
diff --git a/lib/libm/ilogb.c b/lib/libm/ilogb.c
new file mode 100644
index 00000000..3487d460
--- /dev/null
+++ b/lib/libm/ilogb.c
@@ -0,0 +1,30 @@
+#include <limits.h>
+#include "libm.h"
+
+int ilogb(double x)
+{
+#pragma STDC FENV_ACCESS ON
+	union {
+		double f;
+		uint64_t i;
+	} u = { x };
+	uint64_t i = u.i;
+	int e = i >> 52 & 0x7ff;
+
+	if (!e) {
+		i <<= 12;
+		if (i == 0) {
+			FORCE_EVAL(0 / 0.0f);
+			return FP_ILOGB0;
+		}
+		/* subnormal x */
+		for (e = -0x3ff; i >> 63 == 0; e--, i <<= 1)
+			;
+		return e;
+	}
+	if (e == 0x7ff) {
+		FORCE_EVAL(0 / 0.0f);
+		return i << 12 ? FP_ILOGBNAN : INT_MAX;
+	}
+	return e - 0x3ff;
+}