Add a "fork" of musl as //fusl.

fusl/src/math/nextafterf.c

Index: fusl/src/math/nextafterf.c
diff --git a/fusl/src/math/nextafterf.c b/fusl/src/math/nextafterf.c
new file mode 100644
index 0000000000000000000000000000000000000000..75a09f7d1cf115d9a5d5dfeda9b12d42de269904
--- /dev/null
+++ b/fusl/src/math/nextafterf.c
@@ -0,0 +1,30 @@
+#include "libm.h"
+
+float nextafterf(float x, float y)
+{
+	union {float f; uint32_t i;} ux={x}, uy={y};
+	uint32_t ax, ay, e;
+
+	if (isnan(x) || isnan(y))
+		return x + y;
+	if (ux.i == uy.i)
+		return y;
+	ax = ux.i & 0x7fffffff;
+	ay = uy.i & 0x7fffffff;
+	if (ax == 0) {
+		if (ay == 0)
+			return y;
+		ux.i = (uy.i & 0x80000000) | 1;
+	} else if (ax > ay || ((ux.i ^ uy.i) & 0x80000000))
+		ux.i--;
+	else
+		ux.i++;
+	e = ux.i & 0x7f800000;
+	/* raise overflow if ux.f is infinite and x is finite */
+	if (e == 0x7f800000)
+		FORCE_EVAL(x+x);
+	/* raise underflow if ux.f is subnormal or zero */
+	if (e == 0)
+		FORCE_EVAL(x*x + ux.f*ux.f);
+	return ux.f;
+}