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 have logical names as parts of the design data and 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 that uniquely digests functional data design within the 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.