1. A computer-implemented method for automated design of a circuit specified by a machine-readable file having a specified timing constraint, comprising: identifying, using a computer system, a set of timing endpoints for corresponding circuit paths in the circuit defined by the machine-readable file, wherein said corresponding circuit paths include respective sets of components; assigning, using the computer system, respective values for slack for the timing endpoints in said set of timing endpoints, said values represented by respective probability distribution functions; and processing said respective values for slack to produce a combined probability distribution representing said set of timing endpoints, by combining the probability distribution functions representing the respective values of slack, the combined probability distribution being weighted in favor of probability distribution functions for values for slack of timing endpoints having negative slack.