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

fusl/src/math/asinf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/e_asinf.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 double
+pio2 = 1.570796326794896558e+00;
+
+static const float
+/* coefficients for R(x^2) */
+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 asinf(float x)
+{
+        double s;
+        float z;
+        uint32_t hx,ix;
+
+        GET_FLOAT_WORD(hx, x);
+        ix = hx & 0x7fffffff;
+        if (ix >= 0x3f800000) {  /* |x| >= 1 */
+                if (ix == 0x3f800000)  /* |x| == 1 */
+                        return x*pio2 + 0x1p-120f;  /* asin(+-1) = +-pi/2 with inexact */
+                return 0/(x-x);  /* asin(|x|>1) is NaN */
+        }
+        if (ix < 0x3f000000) {  /* |x| < 0.5 */
+                /* if 0x1p-126 <= |x| < 0x1p-12, avoid raising underflow */
+                if (ix < 0x39800000 && ix >= 0x00800000)
+                        return x;
+                return x + x*R(x*x);
+        }
+        /* 1 > |x| >= 0.5 */
+        z = (1 - fabsf(x))*0.5f;
+        s = sqrt(z);
+        x = pio2 - 2*(s+s*R(z));
+        if (hx >> 31)
+                return -x;
+        return x;
+}