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

fusl/src/math/sinh.c

+#include "libm.h"
+
+/* sinh(x) = (exp(x) - 1/exp(x))/2
+ *         = (exp(x)-1 + (exp(x)-1)/exp(x))/2
+ *         = x + x^3/6 + o(x^5)
+ */
+double sinh(double x)
+{
+        union {double f; uint64_t i;} u = {.f = x};
+        uint32_t w;
+        double t, h, absx;
+
+        h = 0.5;
+        if (u.i >> 63)
+                h = -h;
+        /* |x| */
+        u.i &= (uint64_t)-1/2;
+        absx = u.f;
+        w = u.i >> 32;
+
+        /* |x| < log(DBL_MAX) */
+        if (w < 0x40862e42) {
+                t = expm1(absx);
+                if (w < 0x3ff00000) {
+                        if (w < 0x3ff00000 - (26<<20))
+                                /* note: inexact and underflow are raised by expm1 */
+                                /* note: this branch avoids spurious underflow */
+                                return x;
+                        return h*(2*t - t*t/(t+1));
+                }
+                /* note: |x|>log(0x1p26)+eps could be just h*exp(x) */
+                return h*(t + t/(t+1));
+        }
+
+        /* |x| > log(DBL_MAX) or nan */
+        /* note: the result is stored to handle overflow */
+        t = 2*h*__expo2(absx);
+        return t;
+}