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

fusl/src/math/sincos.c

Index: fusl/src/math/sincos.c
diff --git a/fusl/src/math/sincos.c b/fusl/src/math/sincos.c
new file mode 100644
index 0000000000000000000000000000000000000000..35b2d923968f1b5deaaf7e4183c288c2d2a05043
--- /dev/null
+++ b/fusl/src/math/sincos.c
@@ -0,0 +1,69 @@
+/* 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;
+	}
+}