// range 2..64 shows that values of 8 and 16 work well, with a 4x speedup at medium lengths and
// ~30x for 20000 digits. Use nat_test.go's BenchmarkLeafSize tests to optimize leafSize for
// specific hardware.
func (q nat) convertWords(s []byte, b Word, ndigits int, bb Word, table []divisor) {
	// split larger blocks recursively
	if table != nil {