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

fusl/src/math/atan2l.c

+/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2l.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 atan2.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 atan2l(long double y, long double x)
+{
+        return atan2(y, x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+#include "__invtrigl.h"
+
+long double atan2l(long double y, long double x)
+{
+        union ldshape ux, uy;
+        long double z;
+        int m, ex, ey;
+
+        if (isnan(x) || isnan(y))
+                return x+y;
+        if (x == 1)
+                return atanl(y);
+        ux.f = x;
+        uy.f = y;
+        ex = ux.i.se & 0x7fff;
+        ey = uy.i.se & 0x7fff;
+        m = 2*(ux.i.se>>15) | uy.i.se>>15;
+        if (y == 0) {
+                switch(m) {
+                case 0:
+                case 1: return y;           /* atan(+-0,+anything)=+-0 */
+                case 2: return  2*pio2_hi;  /* atan(+0,-anything) = pi */
+                case 3: return -2*pio2_hi;  /* atan(-0,-anything) =-pi */
+                }
+        }
+        if (x == 0)
+                return m&1 ? -pio2_hi : pio2_hi;
+        if (ex == 0x7fff) {
+                if (ey == 0x7fff) {
+                        switch(m) {
+                        case 0: return  pio2_hi/2;   /* atan(+INF,+INF) */
+                        case 1: return -pio2_hi/2;   /* atan(-INF,+INF) */
+                        case 2: return  1.5*pio2_hi; /* atan(+INF,-INF) */
+                        case 3: return -1.5*pio2_hi; /* atan(-INF,-INF) */
+                        }
+                } else {
+                        switch(m) {
+                        case 0: return  0.0;        /* atan(+...,+INF) */
+                        case 1: return -0.0;        /* atan(-...,+INF) */
+                        case 2: return  2*pio2_hi;  /* atan(+...,-INF) */
+                        case 3: return -2*pio2_hi;  /* atan(-...,-INF) */
+                        }
+                }
+        }
+        if (ex+120 < ey || ey == 0x7fff)
+                return m&1 ? -pio2_hi : pio2_hi;
+        /* z = atan(|y/x|) without spurious underflow */
+        if ((m&2) && ey+120 < ex)  /* |y/x| < 0x1p-120, x<0 */
+                z = 0.0;
+        else
+                z = atanl(fabsl(y/x));
+        switch (m) {
+        case 0: return z;               /* atan(+,+) */
+        case 1: return -z;              /* atan(-,+) */
+        case 2: return 2*pio2_hi-(z-2*pio2_lo); /* atan(+,-) */
+        default: /* case 3 */
+                return (z-2*pio2_lo)-2*pio2_hi; /* atan(-,-) */
+        }
+}
+#endif