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

fusl/src/math/__cosdf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/k_cosf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ * Debugged and optimized by Bruce D. Evans.
+ */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#include "libm.h"
+
+/* |cos(x) - c(x)| < 2**-34.1 (~[-5.37e-11, 5.295e-11]). */
+static const double
+C0  = -0x1ffffffd0c5e81.0p-54, /* -0.499999997251031003120 */
+C1  =  0x155553e1053a42.0p-57, /*  0.0416666233237390631894 */
+C2  = -0x16c087e80f1e27.0p-62, /* -0.00138867637746099294692 */
+C3  =  0x199342e0ee5069.0p-68; /*  0.0000243904487962774090654 */
+
+float __cosdf(double x)
+{
+        double_t r, w, z;
+
+        /* Try to optimize for parallel evaluation as in __tandf.c. */
+        z = x*x;
+        w = z*z;
+        r = C2+z*C3;
+        return ((1.0+z*C0) + w*C1) + (w*z)*r;
+}