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

fusl/src/math/cosl.c

Index: fusl/src/math/cosl.c
diff --git a/fusl/src/math/cosl.c b/fusl/src/math/cosl.c
new file mode 100644
index 0000000000000000000000000000000000000000..79c41c77fa6a0addc57e33c62f31d879392b36e6
--- /dev/null
+++ b/fusl/src/math/cosl.c
@@ -0,0 +1,39 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double cosl(long double x) {
+	return cos(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+long double cosl(long double x)
+{
+	union ldshape u = {x};
+	unsigned n;
+	long double y[2], hi, lo;
+
+	u.i.se &= 0x7fff;
+	if (u.i.se == 0x7fff)
+		return x - x;
+	x = u.f;
+	if (x < M_PI_4) {
+		if (u.i.se < 0x3fff - LDBL_MANT_DIG)
+			/* raise inexact if x!=0 */
+			return 1.0 + x;
+		return __cosl(x, 0);
+	}
+	n = __rem_pio2l(x, y);
+	hi = y[0];
+	lo = y[1];
+	switch (n & 3) {
+	case 0:
+		return __cosl(hi, lo);
+	case 1:
+		return -__sinl(hi, lo, 1);
+	case 2:
+		return -__cosl(hi, lo);
+	case 3:
+	default:
+		return __sinl(hi, lo, 1);
+	}
+}
+#endif