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

fusl/src/math/__tandf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/k_tanf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ * Optimized by Bruce D. Evans.
+ */
+/*
+ * ====================================================
+ * Copyright 2004 Sun Microsystems, Inc.  All Rights Reserved.
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#include "libm.h"
+
+/* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */
+static const double T[] = {
+  0x15554d3418c99f.0p-54, /* 0.333331395030791399758 */
+  0x1112fd38999f72.0p-55, /* 0.133392002712976742718 */
+  0x1b54c91d865afe.0p-57, /* 0.0533812378445670393523 */
+  0x191df3908c33ce.0p-58, /* 0.0245283181166547278873 */
+  0x185dadfcecf44e.0p-61, /* 0.00297435743359967304927 */
+  0x1362b9bf971bcd.0p-59, /* 0.00946564784943673166728 */
+};
+
+float __tandf(double x, int odd)
+{
+        double_t z,r,w,s,t,u;
+
+        z = x*x;
+        /*
+         * Split up the polynomial into small independent terms to give
+         * opportunities for parallel evaluation.  The chosen splitting is
+         * micro-optimized for Athlons (XP, X64).  It costs 2 multiplications
+         * relative to Horner's method on sequential machines.
+         *
+         * We add the small terms from lowest degree up for efficiency on
+         * non-sequential machines (the lowest degree terms tend to be ready
+         * earlier).  Apart from this, we don't care about order of
+         * operations, and don't need to to care since we have precision to
+         * spare.  However, the chosen splitting is good for accuracy too,
+         * and would give results as accurate as Horner's method if the
+         * small terms were added from highest degree down.
+         */
+        r = T[4] + z*T[5];
+        t = T[2] + z*T[3];
+        w = z*z;
+        s = z*x;
+        u = T[0] + z*T[1];
+        r = (x + s*u) + (s*w)*(t + w*r);
+        return odd ? -1.0/r : r;
+}