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

fusl/src/math/sincos.c

+/* origin: FreeBSD /usr/src/lib/msun/src/s_sin.c */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+#define _GNU_SOURCE
+#include "libm.h"
+
+void sincos(double x, double *sin, double *cos)
+{
+        double y[2], s, c;
+        uint32_t ix;
+        unsigned n;
+
+        GET_HIGH_WORD(ix, x);
+        ix &= 0x7fffffff;
+
+        /* |x| ~< pi/4 */
+        if (ix <= 0x3fe921fb) {
+                /* if |x| < 2**-27 * sqrt(2) */
+                if (ix < 0x3e46a09e) {
+                        /* raise inexact if x!=0 and underflow if subnormal */
+                        FORCE_EVAL(ix < 0x00100000 ? x/0x1p120f : x+0x1p120f);
+                        *sin = x;
+                        *cos = 1.0;
+                        return;
+                }
+                *sin = __sin(x, 0.0, 0);
+                *cos = __cos(x, 0.0);
+                return;
+        }
+
+        /* sincos(Inf or NaN) is NaN */
+        if (ix >= 0x7ff00000) {
+                *sin = *cos = x - x;
+                return;
+        }
+
+        /* argument reduction needed */
+        n = __rem_pio2(x, y);
+        s = __sin(y[0], y[1], 1);
+        c = __cos(y[0], y[1]);
+        switch (n&3) {
+        case 0:
+                *sin = s;
+                *cos = c;
+                break;
+        case 1:
+                *sin = c;
+                *cos = -s;
+                break;
+        case 2:
+                *sin = -s;
+                *cos = -c;
+                break;
+        case 3:
+        default:
+                *sin = -c;
+                *cos = s;
+                break;
+        }
+}