511
Handling Files that Do Not Fit in Memory
One way to do this is to scan the files sequentially to compute hash codes of
the lines and put the lines in equivalence classes based only on hash code.
Then compare the files normally. This does produce some false matches.
Then scan the two files sequentially again, checking each match to see whether
it is real. When a match is not real, mark both the "matching" lines as
changed. Then build an edit script as usual.
The output routines would have to be changed to scan the files sequentially
looking for the text to print.