Document TTEntry and move layouts

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/move.h

@@ -38,10 +38,22 @@
 
 class Position;
 
+/// A move needs 17 bits to be stored
+///
+/// bit  0- 5: destination square (from 0 to 63)
+/// bit  6-11: origin square (from 0 to 63)
+/// bit 12-14: promotion piece type
+/// bit    15: en passant flag
+/// bit    16: castle flag
+///
+/// Special cases are MOVE_NONE and MOVE_NULL. We can sneak these in
+/// because in any normal move destination square is always different
+/// from origin square while MOVE_NONE and MOVE_NULL have the same
+/// origin and destination square, 0 and 1 respectively.
+
 enum Move {
   MOVE_NONE = 0,
-  MOVE_NULL = 65,
-  MOVE_MAX = 0xFFFFFF
+  MOVE_NULL = 65
 };
 
 
@@ -56,11 +68,11 @@ struct MoveStack {
 ////
 
 inline Square move_from(Move m) {
-  return Square((int(m) >> 6) & 077);
+  return Square((int(m) >> 6) & 0x3F);
 }
 
 inline Square move_to(Move m) {
-  return Square(m & 077);
+  return Square(m & 0x3F);
 }
 
 inline PieceType move_promotion(Move m) {

src/tt.h

@@ -34,7 +34,21 @@
 //// Types
 ////
 
-/// The TTEntry class is the class of transposition table entries.
+/// The TTEntry class is the class of transposition table entries
+///
+/// A TTEntry needs 128 bits to be stored
+///
+/// bit    0-63: key
+/// bit   64-95: data
+/// bit  96-111: value
+/// bit 112-127: depth
+///
+/// the 32 bits of the data field are so defined
+///
+/// bit  0-16: move
+/// bit 17-19: not used
+/// bit 20-22: value type
+/// bit 23-31: generation
 
 class TTEntry {