We propose a new algorithm to find worst cases for correct rounding of an analytic function. We first reduce this problem to the Real Small Value Problem --- i.e. for polynomials with real coefficients. Then we show that this second problem can be solved efficiently, by extending Coppersmith's work on the Integer Small Value Problem --- for polynomials with integer coefficients --- using lattice reduction. For floating-point numbers with a mantissa less than N, and a polynomial approximation of degree d, our algorithm finds all worst cases at distance $