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`Fifteen' was getting the parity wrong on any size of board where

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the top left and bottom right corners didn't have the same
chessboard colour.

[originally from svn r4185]
This commit is contained in:
Simon Tatham
2004-05-03 07:56:23 +00:00
parent e8f6124996
commit eb88ee0973
1 changed files with 5 additions and 4 deletions
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9
fifteen.c
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@ -199,15 +199,16 @@ char *new_game_seed(game_params *params)
* Determine the required parity of the overall permutation.
* This is the XOR of:
*
* - The chessboard parity ((x^y)&1) of the gap square. The
* bottom right, and therefore also the top left, count as
* even.
* - The chessboard parity ((x^y)&1) of the gap square. The
* bottom right counts as even.
*
* - The parity of n. (The target permutation is 1,...,n-1,0
* rather than 0,...,n-1; this is a cyclic permutation of
* the starting point and hence is odd iff n is even.)
*/
parity = (X(params, gap) ^ Y(params, gap) ^ (n+1)) & 1;
parity = ((X(params, gap) - (params->w-1)) ^
(Y(params, gap) - (params->h-1)) ^
(n+1)) & 1;
/*
* Try the last two tiles one way round. If that fails, swap