  A new method is proposed for extrapolation of elastic-scattering data to the
negative-energy region for a short-range interaction. The method is based on
the analytic approximation of the modulus-squared of the partial-wave
scattering amplitude. It is shown that the proposed method has an advantage
over the traditional one based on continuation of the effective-range function.
The new method has been applied to determine the asymptotic normalization
coefficients for the $^{17}$O and $^{13}$C nuclei in the $n+^{16}$O and
$n+^{12}$C channels, respectively.
