SRLI	$1, X5, F1			// ERROR "expected integer register in rd position but got non-integer register F1"
	SRLI	$1, F1, X5			// ERROR "expected integer register in rs1 position but got non-integer register F1"
	FNES	F1, (X5)			// ERROR "needs an integer register output"

type urlFrag struct {
	url, frag string
}

var (
	mu          sync.Mutex
	crawled     = make(map[string]bool)      // URL without fragment -> true
	neededFrags = make(map[urlFrag][]string) // URL#frag -> who needs it
)

var aRx = regexp.MustCompile(`<a href=['"]?(/[^\s'">]+)`)

// Owned by crawlLoop goroutine:
var (
	linkSources = make(map[string][]string) // url no fragment -> sources
	fragExists  = make(map[urlFrag]bool)

// Int promises that the zero value is a 0, but in gmp
// the zero value is a crash.  To bridge the gap, the
// init bool says whether this is a valid gmp value.
// doinit initializes z.i if it needs it.  This is not inherent
// to FFI, just a mismatch between Go's convention of
// making zero values useful and gmp's decision not to.
func (z *Int) doinit() {
	if z.init {
		return
	}
	z.init = true