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

fusl/src/math/acosl.c

Index: fusl/src/math/acosl.c
diff --git a/fusl/src/math/acosl.c b/fusl/src/math/acosl.c
new file mode 100644
index 0000000000000000000000000000000000000000..c03bdf0235ccffd08ca26b603531a9defe11070a
--- /dev/null
+++ b/fusl/src/math/acosl.c
@@ -0,0 +1,67 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_acosl.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+/*
+ * See comments in acos.c.
+ * Converted to long double by David Schultz <das@FreeBSD.ORG>.
+ */
+
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double acosl(long double x)
+{
+	return acos(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+#include "__invtrigl.h"
+#if LDBL_MANT_DIG == 64
+#define CLEARBOTTOM(u) (u.i.m &= -1ULL << 32)
+#elif LDBL_MANT_DIG == 113
+#define CLEARBOTTOM(u) (u.i.lo = 0)
+#endif
+
+long double acosl(long double x)
+{
+	union ldshape u = {x};
+	long double z, s, c, f;
+	uint16_t e = u.i.se & 0x7fff;
+
+	/* |x| >= 1 or nan */
+	if (e >= 0x3fff) {
+		if (x == 1)
+			return 0;
+		if (x == -1)
+			return 2*pio2_hi + 0x1p-120f;
+		return 0/(x-x);
+	}
+	/* |x| < 0.5 */
+	if (e < 0x3fff - 1) {
+		if (e < 0x3fff - LDBL_MANT_DIG - 1)
+			return pio2_hi + 0x1p-120f;
+		return pio2_hi - (__invtrigl_R(x*x)*x - pio2_lo + x);
+	}
+	/* x < -0.5 */
+	if (u.i.se >> 15) {
+		z = (1 + x)*0.5;
+		s = sqrtl(z);
+		return 2*(pio2_hi - (__invtrigl_R(z)*s - pio2_lo + s));
+	}
+	/* x > 0.5 */
+	z = (1 - x)*0.5;
+	s = sqrtl(z);
+	u.f = s;
+	CLEARBOTTOM(u);
+	f = u.f;
+	c = (z - f*f)/(s + f);
+	return 2*(__invtrigl_R(z)*s + c + f);
+}
+#endif