1. A computer-implemented method of evaluating similarities and/or differences between design data for circuits, the design data residing in at least two files stored in computer memory, the method including: using a computer, identifying cells within design data residing in first and second files, wherein the cells correspond to portions of design for a physical circuit; parsing syntax of and normalizing the design data within the cells into canonical forms, wherein the canonical forms reduce sensitivity of data analysis to non-functional variations in the design data within a particular cell; calculating and storing digests of at least selected design data in the canonical forms, producing at least one digest per cell; comparing the digests of the cells in the first file to the digests of the cells in the second file; and summarizing at least some results of the comparing of the digests.