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

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

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/libc/src/musl-math/scalbn.c b/lib/libc/src/musl-math/scalbn.c
new file mode 100644
index 0000000..182f561
--- /dev/null
+++ b/lib/libc/src/musl-math/scalbn.c
@@ -0,0 +1,33 @@
+#include <math.h>
+#include <stdint.h>
+
+double scalbn(double x, int n)
+{
+	union {double f; uint64_t i;} u;
+	double_t y = x;
+
+	if (n > 1023) {
+		y *= 0x1p1023;
+		n -= 1023;
+		if (n > 1023) {
+			y *= 0x1p1023;
+			n -= 1023;
+			if (n > 1023)
+				n = 1023;
+		}
+	} else if (n < -1022) {
+		/* make sure final n < -53 to avoid double
+		   rounding in the subnormal range */
+		y *= 0x1p-1022 * 0x1p53;
+		n += 1022 - 53;
+		if (n < -1022) {
+			y *= 0x1p-1022 * 0x1p53;
+			n += 1022 - 53;
+			if (n < -1022)
+				n = -1022;
+		}
+	}
+	u.i = (uint64_t)(0x3ff+n)<<52;
+	x = y * u.f;
+	return x;
+}