53647: Why doesn't it start a move earlier?

[drahacikfm]

Richard,

53647

From my understanding of how your generator works, I wonder why this problem didn't start a move earlier?  It is obvious from Black's last move Kg8-h8 that White's previous move was Nf7-h6+.  And Nh6+ is mate in 3.  So why did the problem start after Kh8 so that it is only a mate in 2?

I've seen a number of problems where it is obvious what White's previous move was, and it seems the problem could have started a move earlier and still meet all the requirements of the generator.

[richard]

Hi Drahacik,

The generator that produced that problem had two code paths for mates, one where the game being processed ended in actual mate and the other where the game didn't end in mate (i.e. the loser resigned before mate was given).  For the first case the generator would look backwards to find the longest mate available but for the second case the generator would give the longest mate from the point at which the generator first found mate (while moving backwards from the end of the game).  The latest generator now treats both cases the same and when it finds a mate even if the actual game didn't end in mate then it should walk backwards to find the longest mate.

Richard.