+# Returns a compact bit string describing the same data as fen(),
+# except for the half-move and full-move clock.
+sub bitpacked_fen {
+ my $pos = shift;
+ my $board = $pos->{'board'}->bitpacked_fen();
+
+ my $bits = "";
+ if ($pos->{'toplay'} eq 'W') {
+ $bits .= "0";
+ } else {
+ $bits .= "1";
+ }
+
+ $bits .= $pos->{'white_castle_k'};
+ $bits .= $pos->{'white_castle_q'};
+ $bits .= $pos->{'black_castle_k'};
+ $bits .= $pos->{'black_castle_q'};
+
+ my $col = $pos->{'ep_file_num'};
+ if ($col == -1) {
+ $bits .= "0";
+ } else {
+ $bits .= "1";
+ $bits .= (qw(000 001 010 011 100 101 110 111))[$col];
+ }
+
+ return $board . pack('b*', $bits);
+}
+