Would you like to apply the advices from the article "http://en.wikipedia.org/wiki/Const-correctness" to more places in your sources?
I suggest to add the key word "const" to the type specifiers for parameters like the following.
r1, r2 (function "doDiff")
rep (function "MatchOp::calcSize")
http://re2c.svn.sourceforge.net/viewvc/re2c/trunk/re2c/actions.cc?revision=896&view=markup
http://re2c.svn.sourceforge.net/viewvc/re2c/trunk/re2c/re.h?revision=850&view=markup