README finished

README.md

@@ -24,7 +24,8 @@ targets:
 - chessNoComputer: The user can play both sides in a GUI. Mainly added for testing the move
   generator.
 - findMagicNumber: finds Magic Numbers for the magic bitboard.
-- moveGenTest: tests the move generator
+- moveGenTest: tests the move generator,
+- genMoveConsts: produces constants to generate moves faster.
 
 ## Testing
 
@@ -43,8 +44,30 @@ use bitwise operations to calculate information we need, really fast.
 The move generation of pseudo-legal moves (moves without considering whether the
 king is in check) is mostly straightforward. We pre-generate some data in
 `src/generateCode/moveConsts.c`, so that we can calculate the moves faster.
+For the king and the knight the moves are pre-generated because they can only
+possibly move to fixed target squares for one given source square. For the other
+pieces we pre-generated the distance, the piece can move in one given direction.
 
-# sources
+For testing, if the king is in check, so we get legal moves, [magic
+Bitboards](https://www.chessprogramming.org/Magic_Bitboards) are used. This
+allows us to calculate really fast whether the king is in check compared to
+looping over all moves to see, if a piece can capture the king. Essentially we
+get the bitboard of all pieces and null all bits but the file and rank, the rook
+we want to the moves for, is on (or the relevant diagonals for the bishop). We
+can look up the moves by using this mask as a key of a hashmap. A hashing
+algorithm that multiplies with a so-called magic number and right shift, is used.
+The hashing is fast, and we can find magic numbers, so there are no hash
+collisions. To simplify the task of finding magic numbers, we use a different
+magic number for each square ([fancy magic
+bitboard](https://www.chessprogramming.org/Magic_Bitboards#Fancy)). The magic
+numbers for this engine are simply found by trying randomly generated one. The
+Implementation in `src/findMagicNumber.c` is based on ideas
+[there](https://www.chessprogramming.org/Looking_for_Magics#Feeding_in_Randoms).
 
-https://www.chessprogramming.org/Magic_Bitboards
-https://www.chessprogramming.org/Looking_for_Magics
+For seraching the moves, we use a variant of [Alpha-Beta](https://www.chessprogramming.org/Alpha-Beta).
+Alpha-Beta is based on [minimax](https://en.wikipedia.org/wiki/Minimax) with an
+added upper and lower bound for the position score with makes it much faster
+than minimax.
+
+The evaluation is currently simple because the only keeps track of the material
+and checkmate. Here is currently the most room for optimizations.