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

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

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/libc/src/musl-math/floor.c b/lib/libc/src/musl-math/floor.c
new file mode 100644
index 0000000..14a31cd
--- /dev/null
+++ b/lib/libc/src/musl-math/floor.c
@@ -0,0 +1,31 @@
+#include "libm.h"
+
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
+double floor(double x)
+{
+	union {double f; uint64_t i;} u = {x};
+	int e = u.i >> 52 & 0x7ff;
+	double_t y;
+
+	if (e >= 0x3ff+52 || x == 0)
+		return x;
+	/* y = int(x) - x, where int(x) is an integer neighbor of x */
+	if (u.i >> 63)
+		y = x - toint + toint - x;
+	else
+		y = x + toint - toint - x;
+	/* special case because of non-nearest rounding modes */
+	if (e <= 0x3ff-1) {
+		FORCE_EVAL(y);
+		return u.i >> 63 ? -1 : 0;
+	}
+	if (y > 0)
+		return x + y - 1;
+	return x + y;
+}