mirror of
https://github.com/StewBC/cc65-Chess.git
synced 2026-10-25 01:02:25 +00:00
Stefan WesselsandClaude Opus 5
4512ab9529
The failure is more instructive than the fix, and the original is not bad code - which is what makes it worth reading. Two structural decisions made it weak, both of them traps that are well known inside computer chess and close to invisible from outside it: The attack database became the legality oracle. It is the right structure for the attacker/defender display it was built for, and reusing it to answer "is my king attacked" is the natural next thought - but it meant testing one move for legality cost a full 64-square regeneration, and legality is the innermost loop of the whole program. The evaluation scored move desirability rather than position value. Each scoring function is individually sensible; the quantity is not a property of the position, so it cannot be negated for the opponent, so accumulating it across plies does not describe anything. This is the one that mattered most: the database made it slow, but this made depth not help. Also covers what followed from those two - mate detection as special-case machinery mutating a shared structure, promotion decided during make rather than encoded in the move - and a positional-initialiser hazard in gPieceValues where the comments run in a different order from the enum, so the king and queen values landed swapped. Leads with what the original got right, because it is the reason the rework could port the movement rules rather than rederive them: the generator was perft-exact to depth 5 on two reference positions, with one divergence, and that divergence was a design choice rather than a bug. Every excerpt and figure checked against the source at v1-original-engine. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>