usr: libc: Add math.h + musl math impl portexpt

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/libc/src/musl-math/logb.c b/lib/libc/src/musl-math/logb.c
new file mode 100644
index 0000000..7f8bdfa
--- /dev/null
+++ b/lib/libc/src/musl-math/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);
+}