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--- chess:programming:zobrist_hashing [2021/10/30 21:26] – peter
+++ chess:programming:zobrist_hashing [2021/10/30 21:41] (current) – [Implementation Consideration] peter
@@ Line 1: / Line 1: @@
 ====== Chess - Programming - Zobrist Hashing ======
-**Zobrist Hashing** is a technique to transform a board position of arbitrary size into a number of a set length, with an equal distribution over all possible numbers.
+**Zobrist Hashing** is a hashing function that is widely used in 2 player board games.
   * The main purpose of Zobrist hash codes in chess programming is to get an almost unique index number for any chess position, with a very important requirement that two similar positions generate entirely different indices.
-  * These index numbers are used for faster and more space efficient Hash tables or databases, e.g. transposition tables and opening books.
+  * It is the most common hashing function used in transposition tables; and sometimes opening books.
+  * Transposition tables basically store the evaluated values of previous board states, so that if they are encountered again we simply retrieve the stored value from the transposition table.
+  * These index numbers are used for faster and more space efficient Hash tables or databases.
 ----
 [[Chess:Programming:Zobrist Hashing:A program to illustrate the Zobrist Hashing Algorithm|A program to illustrate the Zobrist Hashing Algorithm]]
-----
-Zobrist Hashing is a hashing function that is widely used in 2 player board games.
-  * It is the most common hashing function used in transposition tables.
-  * Transposition tables basically store the evaluated values of previous board states, so that if they are encountered again we simply retrieve the stored value from the transposition table.
 ----
@@ Line 22: / Line 17: @@
 <code>
-// A matrix with random numbers initialized once
+// A matrix with random numbers initialized once.
 Table[#ofBoardCells][#ofPieces]
-// Returns Zobrist hash function for current conf-
+// Returns Zobrist hash function for current configuration of board.
-// iguration of board.
 function findhash(board):
-    hash = 0
+  hash = 0
-    for each cell on the board :
+  for each cell on the board :
-        if cell is not empty :
+    if cell is not empty :
-            piece = board[cell]
+      piece = board[cell]
-            hash ^= table[cell][piece]
+      hash ^= table[cell][piece]
-    return hash
+  return hash
 </code>
@@ Line 167: / Line 161: @@
 <code cpp>
-piece*color*square * 8 + 3*8) bits;
+(piece*color*square * 8 + 3*8) bits;
 </code>
   * This will reduce array of about 8th in size.
-If a bit boundary is used, the array becomes
+If a bit boundary is used, the array becomes:
 <code cpp>
-piece*color*square + 63) bits;
+(piece*color*square + 63) bits;
 </code>