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

fusl/src/math/floor.c

+#include "libm.h"
+
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
+double floor(double x)
+{
+        union {double f; uint64_t i;} u = {x};
+        int e = u.i >> 52 & 0x7ff;
+        double_t y;
+
+        if (e >= 0x3ff+52 || x == 0)
+                return x;
+        /* y = int(x) - x, where int(x) is an integer neighbor of x */
+        if (u.i >> 63)
+                y = x - toint + toint - x;
+        else
+                y = x + toint - toint - x;
+        /* special case because of non-nearest rounding modes */
+        if (e <= 0x3ff-1) {
+                FORCE_EVAL(y);
+                return u.i >> 63 ? -1 : 0;
+        }
+        if (y > 0)
+                return x + y - 1;
+        return x + y;
+}