void bbcopy_slow(struct fastbuf *f, struct fastbuf *t, uns l);
/**
* Copy @l bytes of data from fastbuf @f to fastbuf @t.
+ * `UINT_MAX` (`~0U`) means all data, even if more than `UINT_MAX` bytes remain.
**/
static inline void bbcopy(struct fastbuf *f, struct fastbuf *t, uns l)
{