lib/libm: Add implementation of nearbyintf, from musl-1.1.16.

lib/libm/nearbyintf.c

@@ -0,0 +1,21 @@
+// adapted from the rintf() function from musl-1.1.16
+
+#include "libm.h"
+
+float nearbyintf(float x)
+{
+	union {float f; uint32_t i;} u = {x};
+	int e = u.i>>23 & 0xff;
+	int s = u.i>>31;
+	float_t y;
+
+	if (e >= 0x7f+23)
+		return x;
+	if (s)
+		y = x - 0x1p23f + 0x1p23f;
+	else
+		y = x + 0x1p23f - 0x1p23f;
+	if (y == 0)
+		return s ? -0.0f : 0.0f;
+	return y;
+}