huff.erl

%% Huffman Code for nêhiyawêwin %%
%% Note: Cree strings must be written in "askiy":
%%    - short vowels and consonants: written in ASCII
%%    - long vowels: ê is written as e; "âîô" written as "AIO" respectively.
%%    - it's a very grounded character encoding 😉
%%
%% I haven't done extensive testing, but this usually uses half the bits to
%% represent Cree word forms. Maybe just gzip it instead?
-module(huff).
-export([encode/1, decode/1, tryit/1]).

%% Definitions for huffman code.
-define(K,      2#100     :3).
-define(A,      2#010     :3).
-define(I,      2#001     :3).
-define(EE,     2#1100    :4).
-define(W,      2#1011    :4).
-define(AA,     2#1010    :4).
-define(N,      2#0111    :4).
-define(T,      2#0110    :4).
-define(M,      2#0001    :4).
-define(S,      2#11111   :5).
-define(H,      2#11110   :5).
-define(HYPHEN, 2#11101   :5).
-define(Y,      2#11100   :5).
-define(O,      2#11010   :5).
-define(II,     2#00001   :5).
-define(P,      2#00000   :5).
-define(OO,     2#110111  :6).
-define(C,      2#1101101 :7).
-define(L,      2#11011001:8).
-define(R,      2#11011000:8).

% Encodes an SRO string in "askiy".
encode(String) ->
    encode(String, <<>>).

encode([], Binary) ->
    Binary;
encode([$k|Rest], Binary) ->
    encode(Rest, <<?K, Binary/bitstring>>);
encode([$a|Rest], Binary) ->
    encode(Rest, <<?A, Binary/bitstring>>);
encode([$i|Rest], Binary) ->
    encode(Rest, <<?I, Binary/bitstring>>);
encode([$e|Rest], Binary) ->
    encode(Rest, <<?EE, Binary/bitstring>>);
encode([$w|Rest], Binary) ->
    encode(Rest, <<?W, Binary/bitstring>>);
encode([$A|Rest], Binary) ->
    encode(Rest, <<?AA, Binary/bitstring>>);
encode([$n|Rest], Binary) ->
    encode(Rest, <<?N, Binary/bitstring>>);
encode([$t|Rest], Binary) ->
    encode(Rest, <<?T, Binary/bitstring>>);
encode([$m|Rest], Binary) ->
    encode(Rest, <<?M, Binary/bitstring>>);
encode([$s|Rest], Binary) ->
    encode(Rest, <<?S, Binary/bitstring>>);
encode([$h|Rest], Binary) ->
    encode(Rest, <<?H, Binary/bitstring>>);
encode([$-|Rest], Binary) ->
    encode(Rest, <<?HYPHEN, Binary/bitstring>>);
encode([$y|Rest], Binary) ->
    encode(Rest, <<?Y, Binary/bitstring>>);
encode([$o|Rest], Binary) ->
    encode(Rest, <<?O, Binary/bitstring>>);
encode([$I|Rest], Binary) ->
    encode(Rest, <<?II, Binary/bitstring>>);
encode([$p|Rest], Binary) ->
    encode(Rest, <<?P, Binary/bitstring>>);
encode([$O|Rest], Binary) ->
    encode(Rest, <<?OO, Binary/bitstring>>);
encode([$c|Rest], Binary) ->
    encode(Rest, <<?C, Binary/bitstring>>);
encode([$l|Rest], Binary) ->
    encode(Rest, <<?L, Binary/bitstring>>);
encode([$r|Rest], Binary) ->
    encode(Rest, <<?R, Binary/bitstring>>).

% Decodes a huffman code to "askiy"
decode(Binary) ->
    decode(Binary, "").
decode(<<>>, String) ->
    String;
decode(<<?K, Rest/bitstring>>, String) ->
    decode(Rest, [$k|String]);
decode(<<?A, Rest/bitstring>>, String) ->
    decode(Rest, [$a|String]);
decode(<<?I, Rest/bitstring>>, String) ->
    decode(Rest, [$i|String]);
decode(<<?EE, Rest/bitstring>>, String) ->
    decode(Rest, [$e|String]);
decode(<<?W, Rest/bitstring>>, String) ->
    decode(Rest, [$w|String]);
decode(<<?AA, Rest/bitstring>>, String) ->
    decode(Rest, [$A|String]);
decode(<<?N, Rest/bitstring>>, String) ->
    decode(Rest, [$n|String]);
decode(<<?T, Rest/bitstring>>, String) ->
    decode(Rest, [$t|String]);
decode(<<?M, Rest/bitstring>>, String) ->
    decode(Rest, [$m|String]);
decode(<<?S, Rest/bitstring>>, String) ->
    decode(Rest, [$s|String]);
decode(<<?H, Rest/bitstring>>, String) ->
    decode(Rest, [$h|String]);
decode(<<?HYPHEN, Rest/bitstring>>, String) ->
    decode(Rest, [$-|String]);
decode(<<?Y, Rest/bitstring>>, String) ->
    decode(Rest, [$y|String]);
decode(<<?O, Rest/bitstring>>, String) ->
    decode(Rest, [$o|String]);
decode(<<?II, Rest/bitstring>>, String) ->
    decode(Rest, [$I|String]);
decode(<<?P, Rest/bitstring>>, String) ->
    decode(Rest, [$p|String]);
decode(<<?OO, Rest/bitstring>>, String) ->
    decode(Rest, [$O|String]);
decode(<<?C, Rest/bitstring>>, String) ->
    decode(Rest, [$c|String]);
decode(<<?L, Rest/bitstring>>, String) ->
    decode(Rest, [$l|String]);
decode(<<?R, Rest/bitstring>>, String) ->
    decode(Rest, [$r|String]).

% Compress a word; determine how many bits were saved.
tryit(Word) ->
    Encoded = encode(Word),
    OriginalSize = 8 * length(Word),
    SizeInBits = erlang:bit_size(Encoded),
    Percentage = 100.0 * SizeInBits / OriginalSize,
    {Encoded, decode(Encoded), SizeInBits, Percentage}.