How to write a parser in C?

What are the ways to write a code for a bottom up parser from the given LR parser  code and compare their efficiencies?

• Answer:

  If you have the LR parser code, then you already have a bottom-up parser, because LR works bottom-up ;) Did you mean top-down? The general answer is that the easiest way is most probably through the grammar. If you can extract it from the code that you have (by reusing the parser spec, by recovering it from the code structure, by looking at comments — whatever, the methods are plenty), then you can transform it (sometimes even automatically, depends on your knowledge of ) to have a suitable form for top-down (or for whatever your favourite parsing technology is), and then to generate it again from that grammar.