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Ryan Mack,
in the late 90s an American teen programmer and inventor of the Reverse Bitboards when he was a 16 year old schoolboy. In 2000, while introducing his Hyperbola Project, he explained the x XOR (x - 2) bit-twiddling trick as the basic idea of Reverse Bitboards, essentially subtracting a rook from a blocking piece, where the changed bits masked on a line remain the sliding ray-attacks in positive ray-directions. His idea to keep a reversed or 180 degree rotated occupancy to apply the same trick for negative ray-directions to yield reversed attack bitboards, either requiring bitboard reversal or disjoint serialization with reversion in the square centric world by xor 63, turned out to be not that successful as the young author initially thought and claimed. However, Hyperbola Quintessence, where fast vertical byteswap flipping is used on the fly to reverse diagonals and files, is somehow the resurrection of Ryan's ideas, vastly improved by Aleks Peshkov's xor wizardry.

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