TalkChess.com

[H.G.Muller]

In WinBoard's position search I currently do the same thing (keeping the original PGN, as well as making a compact, search-friendly version of the moves). The compact representation is just a sequence of (from, to) 8-bit square-number pairs, where an off-board from-square is used as escape for special moves that need extra information (like promotion piece, which is then given in the second byte). There is an index that tells where each game starts in the compact representation, so that you only have to search through them to a point where you can no longer find the position you are looking for (e.g. because the number of pieces has dropped to below what you were looking for), and then skip to the next game.