  We have developed a universal approach to compute accurately the brightness
of eclipsing binary systems during the transit of a planet in front of the
stellar disk. This approach is uniform for all values of the system parameters
and applicable to most limb-darkening laws used in astrophysics. In the cases
of linear and quadratic limb-darkening laws we obtained analytical expressions
for the light curve and its derivatives in terms of elementary functions,
elliptic integrals and piecewise-defined function of one variable. In the cases
of logarithmic and square root laws of limb darkening the flux and its
derivatives were expressed in terms of integrals which can be efficiently
computed using Gaussian quadrature formula, taking into account singularities
of the integrand.
