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

fusl/src/math/acosf.c

Index: fusl/src/math/acosf.c
diff --git a/fusl/src/math/acosf.c b/fusl/src/math/acosf.c
new file mode 100644
index 0000000000000000000000000000000000000000..8ee1a71d0cc2965e08e170be1dc4529d0165f3b4
--- /dev/null
+++ b/fusl/src/math/acosf.c
@@ -0,0 +1,71 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+/*
+ * ====================================================
+ * 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"
+
+static const float
+pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
+pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
+pS0 =  1.6666586697e-01,
+pS1 = -4.2743422091e-02,
+pS2 = -8.6563630030e-03,
+qS1 = -7.0662963390e-01;
+
+static float R(float z)
+{
+	float_t p, q;
+	p = z*(pS0+z*(pS1+z*pS2));
+	q = 1.0f+z*qS1;
+	return p/q;
+}
+
+float acosf(float x)
+{
+	float z,w,s,c,df;
+	uint32_t hx,ix;
+
+	GET_FLOAT_WORD(hx, x);
+	ix = hx & 0x7fffffff;
+	/* |x| >= 1 or nan */
+	if (ix >= 0x3f800000) {
+		if (ix == 0x3f800000) {
+			if (hx >> 31)
+				return 2*pio2_hi + 0x1p-120f;
+			return 0;
+		}
+		return 0/(x-x);
+	}
+	/* |x| < 0.5 */
+	if (ix < 0x3f000000) {
+		if (ix <= 0x32800000) /* |x| < 2**-26 */
+			return pio2_hi + 0x1p-120f;
+		return pio2_hi - (x - (pio2_lo-x*R(x*x)));
+	}
+	/* x < -0.5 */
+	if (hx >> 31) {
+		z = (1+x)*0.5f;
+		s = sqrtf(z);
+		w = R(z)*s-pio2_lo;
+		return 2*(pio2_hi - (s+w));
+	}
+	/* x > 0.5 */
+	z = (1-x)*0.5f;
+	s = sqrtf(z);
+	GET_FLOAT_WORD(hx,s);
+	SET_FLOAT_WORD(df,hx&0xfffff000);
+	c = (z-df*df)/(s+df);
+	w = R(z)*s+c;
+	return 2*(df+w);
+}