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

fusl/src/math/cbrtf.c

+/* origin: FreeBSD /usr/src/lib/msun/src/s_cbrtf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ * Debugged and optimized by Bruce D. Evans.
+ */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+/* cbrtf(x)
+ * Return cube root of x
+ */
+
+#include <math.h>
+#include <stdint.h>
+
+static const unsigned
+B1 = 709958130, /* B1 = (127-127.0/3-0.03306235651)*2**23 */
+B2 = 642849266; /* B2 = (127-127.0/3-24/3-0.03306235651)*2**23 */
+
+float cbrtf(float x)
+{
+        double_t r,T;
+        union {float f; uint32_t i;} u = {x};
+        uint32_t hx = u.i & 0x7fffffff;
+
+        if (hx >= 0x7f800000)  /* cbrt(NaN,INF) is itself */
+                return x + x;
+
+        /* rough cbrt to 5 bits */
+        if (hx < 0x00800000) {  /* zero or subnormal? */
+                if (hx == 0)
+                        return x;  /* cbrt(+-0) is itself */
+                u.f = x*0x1p24f;
+                hx = u.i & 0x7fffffff;
+                hx = hx/3 + B2;
+        } else
+                hx = hx/3 + B1;
+        u.i &= 0x80000000;
+        u.i |= hx;
+
+        /*
+         * First step Newton iteration (solving t*t-x/t == 0) to 16 bits.  In
+         * double precision so that its terms can be arranged for efficiency
+         * without causing overflow or underflow.
+         */
+        T = u.f;
+        r = T*T*T;
+        T = T*((double_t)x+x+r)/(x+r+r);
+
+        /*
+         * Second step Newton iteration to 47 bits.  In double precision for
+         * efficiency and accuracy.
+         */
+        r = T*T*T;
+        T = T*((double_t)x+x+r)/(x+r+r);
+
+        /* rounding to 24 bits is perfect in round-to-nearest mode */
+        return T;
+}