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

fusl/src/math/truncl.c

Index: fusl/src/math/truncl.c
diff --git a/fusl/src/math/truncl.c b/fusl/src/math/truncl.c
new file mode 100644
index 0000000000000000000000000000000000000000..f07b1934097bcbb932e37a8b0710c99738993e39
--- /dev/null
+++ b/fusl/src/math/truncl.c
@@ -0,0 +1,34 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double truncl(long double x)
+{
+	return trunc(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+
+static const long double toint = 1/LDBL_EPSILON;
+
+long double truncl(long double x)
+{
+	union ldshape u = {x};
+	int e = u.i.se & 0x7fff;
+	int s = u.i.se >> 15;
+	long double y;
+
+	if (e >= 0x3fff+LDBL_MANT_DIG-1)
+		return x;
+	if (e <= 0x3fff-1) {
+		FORCE_EVAL(x + 0x1p120f);
+		return x*0;
+	}
+	/* y = int(|x|) - |x|, where int(|x|) is an integer neighbor of |x| */
+	if (s)
+		x = -x;
+	y = x + toint - toint - x;
+	if (y > 0)
+		y -= 1;
+	x += y;
+	return s ? -x : x;
+}
+#endif