+# Returns a compact bit string describing the same data as fen().
+# This is encoded using a Huffman-like encoding, and should be
+# typically about 1/3 the number of bytes.
+sub bitpacked_fen {
+ my ($board) = @_;
+ my $bits = "";
+
+ for my $row (0..7) {
+ for my $col (0..7) {
+ my $piece = $board->[$row][$col];
+ if ($piece eq '-') {
+ $bits .= "0";
+ next;
+ }
+
+ my $color = (lc($piece) eq $piece) ? 0 : 1;
+ $bits .= "1" . $color;
+
+ if (lc($piece) eq 'p') {
+ $bits .= "0";
+ } elsif (lc($piece) eq 'n') {
+ $bits .= "100";
+ } elsif (lc($piece) eq 'b') {
+ $bits .= "101";
+ } elsif (lc($piece) eq 'r') {
+ $bits .= "1110";
+ } elsif (lc($piece) eq 'q') {
+ $bits .= "11110";
+ } elsif (lc($piece) eq 'k') {
+ $bits .= "11111";
+ } else {
+ die "Unknown piece $piece";
+ }
+ }
+ }
+
+ return pack('b*', $bits);
+}
+