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

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

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/libc/src/musl-math/exp10.c b/lib/libc/src/musl-math/exp10.c
new file mode 100644
index 0000000..47b4dc7
--- /dev/null
+++ b/lib/libc/src/musl-math/exp10.c
@@ -0,0 +1,26 @@
+#define _GNU_SOURCE
+#include <math.h>
+#include <stdint.h>
+#include "weak_alias.h"
+//#include "libc.h"
+
+double exp10(double x)
+{
+	static const double p10[] = {
+		1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10,
+		1e-9, 1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1,
+		1, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
+		1e10, 1e11, 1e12, 1e13, 1e14, 1e15
+	};
+	double n, y = modf(x, &n);
+	union {double f; uint64_t i;} u = {n};
+	/* fabs(n) < 16 without raising invalid on nan */
+	if ((u.i>>52 & 0x7ff) < 0x3ff+4) {
+		if (!y) return p10[(int)n+15];
+		y = exp2(3.32192809488736234787031942948939 * y);
+		return y * p10[(int)n+15];
+	}
+	return pow(10.0, x);
+}
+
+weak_alias(exp10, pow10);