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

fusl/src/math/asinl.c

+/* origin: FreeBSD /usr/src/lib/msun/src/e_asinl.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 asin.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 asinl(long double x)
+{
+        return asin(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+#include "__invtrigl.h"
+#if LDBL_MANT_DIG == 64
+#define CLOSETO1(u) (u.i.m>>56 >= 0xf7)
+#define CLEARBOTTOM(u) (u.i.m &= -1ULL << 32)
+#elif LDBL_MANT_DIG == 113
+#define CLOSETO1(u) (u.i.top >= 0xee00)
+#define CLEARBOTTOM(u) (u.i.lo = 0)
+#endif
+
+long double asinl(long double x)
+{
+        union ldshape u = {x};
+        long double z, r, s;
+        uint16_t e = u.i.se & 0x7fff;
+        int sign = u.i.se >> 15;
+
+        if (e >= 0x3fff) {   /* |x| >= 1 or nan */
+                /* asin(+-1)=+-pi/2 with inexact */
+                if (x == 1 || x == -1)
+                        return x*pio2_hi + 0x1p-120f;
+                return 0/(x-x);
+        }
+        if (e < 0x3fff - 1) {  /* |x| < 0.5 */
+                if (e < 0x3fff - (LDBL_MANT_DIG+1)/2) {
+                        /* return x with inexact if x!=0 */
+                        FORCE_EVAL(x + 0x1p120f);
+                        return x;
+                }
+                return x + x*__invtrigl_R(x*x);
+        }
+        /* 1 > |x| >= 0.5 */
+        z = (1.0 - fabsl(x))*0.5;
+        s = sqrtl(z);
+        r = __invtrigl_R(z);
+        if (CLOSETO1(u)) {
+                x = pio2_hi - (2*(s+s*r)-pio2_lo);
+        } else {
+                long double f, c;
+                u.f = s;
+                CLEARBOTTOM(u);
+                f = u.f;
+                c = (z - f*f)/(s + f);
+                x = 0.5*pio2_hi-(2*s*r - (pio2_lo-2*c) - (0.5*pio2_hi-2*f));
+        }
+        return sign ? -x : x;
+}
+#endif