Rice coding in raku

rice.rakumod

unit module Rice;
# L<https://en.wikipedia.org/wiki/Golomb_coding>

our sub encode(Int $n, UInt :$k = 2) {
  my $d = 2**$k;
  my $q = $n div $d;
  my $b = sign(1 + sign($q));
  my $m = abs($q) + $b;
  flat
    $b xx $m, 1 - $b,
    ($n mod $d).polymod(2 xx $k - 1).reverse
}

our proto decode(|) returns Int {*}

multi decode(Channel $c, UInt :$k = 2) {
  my $d = 2**$k;
  my $b = $c.receive;
  my $m = 1;
  $m++ while $c.receive == $b;
  my $q = $b ?? $m - 1 !! -$m;
  $q*$d + ($c.receive xx $k).reduce(2 * * + *);
}

multi decode(@bits, UInt :$k = 2) {
  my Channel $c .= new;
  start { $c.send: $_ for @bits }
  samewith $c, :$k;
}

CHECK {
  use Test;
  constant N = 100;
  plan 2*N + 1;
  is $_, decode encode $_ for -N..N;
}