add extension set pruning to shadow play and word generation#15
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Compute left/right extension sets per strip via GADDAG traversal. Left extension: which tiles can extend leftward (from tiles to the right). Right extension: seek separator from the same node. AND extension sets with cross_set & rack_bits in shadow play to prune tiles that can't extend the main word. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
A non-empty extension set should allow blanks (bit 0), matching how cross sets work. Use bits | (bits != 0) pattern. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
One right-to-left pass per strip computes both left and right extension sets from each tile group's GADDAG node: children give left extension, seek(separator) then children give right extension. No behavioral change. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
AND left_extension_strip and right_extension_strip at every position in both shadow_play_left and shadow_play_right. This adds inline-direction pruning at positions between two tile groups where both extension sets are non-trivial. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
Pre-AND left and right extension sets during computation, storing one combined extension_set per direction instead of separate left/right arrays (4 arrays -> 2). No behavioral change since both were already ANDed at each shadow play position. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
If no tile can extend in either direction at an anchor position, skip shadow play entirely. Avoids accumulator setup and rack tally cloning for provably dead anchors. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
Extension sets are derived from the KWG, so they must be invalidated when switching to a different KWG. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
Word generation needs left and right extension sets separately: play_right uses left_extension (tiles ahead to the right), play_left uses right_extension (tiles ahead to the left). Shadow play continues to AND both at each position. Upfront fill moved out of gen_extension_sets to a single memset per array before the strip loops. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
AND left_extension_strip in play_right and right_extension_strip in play_left before iterating KWG children. This prunes tiles that pass the cross set but cannot extend toward board tiles the traversal hasn't reached yet, avoiding unnecessary KWG arc iterations. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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