1 files changed, 17 insertions, 0 deletions
diff --git a/lib/libm/logb.c b/lib/libm/logb.c
new file mode 100644
index 00000000..f36a9646
--- /dev/null
+++ b/lib/libm/logb.c
@@ -0,0 +1,17 @@
+#include <math.h>
+
+/*
+special cases:
+	logb(+-0) = -inf, and raise divbyzero
+	logb(+-inf) = +inf
+	logb(nan) = nan
+*/
+
+double logb(double x)
+{
+	if (!isfinite(x))
+		return x * x;
+	if (x == 0)
+		return -1 / (x * x);
+	return ilogb(x);
+}