Well, actually it doesn't, because I messed up. One should not test pieceType (which will always be 14 at this point), but imi, to decide which moves to forbid. In addition, I tested for a full square, rather than an empty. The following routine should work: it first declares OK all non-imitator moves, all imitations of non-pawns, and all moves to occupied squares. At that point only non-capture pawn imitations are left, and advances of more than 1 rank can be flagged as illegal. finally it tests for e.p. depending on which pawn type is imitated.
Well, actually it doesn't, because I messed up. One should not test pieceType (which will always be 14 at this point), but imi, to decide which moves to forbid. In addition, I tested for a full square, rather than an empty. The following routine should work: it first declares OK all non-imitator moves, all imitations of non-pawns, and all moves to occupied squares. At that point only non-capture pawn imitations are left, and advances of more than 1 rank can be flagged as illegal. finally it tests for e.p. depending on which pawn type is imitated.
function BadZone(toFile, toRank, pieceType, color, fromFile, fromRank) { if(pieceType != 14) return 0; if((imi & 511) > 2) return 0; if(board[toRank][toFile] & 511) return 0; if(fromRank > toRank + 1 || fromRank < toRank - 1) return 1; if(imi == 1) return (toFile != fromFile); return (toFile == fromFile); }