1 files changed, 28 insertions, 0 deletions
diff --git a/src/math/ilogbl.c b/src/math/ilogbl.c
new file mode 100644
index 00000000..ed9ddcbc
--- /dev/null
+++ b/src/math/ilogbl.c
@@ -0,0 +1,28 @@
+#include <limits.h>
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+int ilogbl(long double x)
+{
+	return ilogb(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+int ilogbl(long double x)
+{
+	union ldshape u = {x};
+	uint64_t m = u.bits.m;
+	int e = u.bits.exp;
+
+	if (!e) {
+		if (m == 0)
+			return FP_ILOGB0;
+		/* subnormal x */
+		for (e = -0x3fff+1; m < (uint64_t)1<<63; e--, m<<=1);
+		return e;
+	}
+	if (e == 0x7fff)
+		/* in ld80 msb is set in inf */
+		return m & (uint64_t)-1>>1 ? FP_ILOGBNAN : INT_MAX;
+	return e - 0x3fff;
+}
+#endif