1 | local math_modf = math.modf |
2 | local string_char = string.char |
3 | local table_concat = table.concat |
4 | |
5 | -------------------------------------------------------------------------------- |
6 | -- LZW codec |
7 | -- implemented by sheets.jeff@gmail.com |
8 | |
9 | -- encode is used to uniquely encode a number into a sequence of bytes that can be decoded using decode() |
10 | -- the bytes returned by this do not contain "\000" |
11 | local bytes = {}
|
12 | |
13 | ---Encode |
14 | --@param x |
15 | local function encode(x) |
16 | for k = 1, #bytes do bytes[k] = nil end |
17 | local xmod |
18 | x, xmod = math_modf(x/255) |
19 | xmod = xmod * 255 |
20 | bytes[#bytes + 1] = xmod |
21 | while x > 0 do |
22 | x, xmod = math_modf(x/255) |
23 | xmod = xmod * 255 |
24 | bytes[#bytes + 1] = xmod |
25 | end |
26 | if #bytes == 1 and bytes[1] > 0 and bytes[1] < 250 then |
27 | return string_char(bytes[1]) |
28 | else |
29 | for i = 1, #bytes do bytes[i] = bytes[i] + 1 end |
30 | return string_char(256 - #bytes, unpack(bytes)) |
31 | end |
32 | end |
33 | |
34 | ---LibCompress, |
35 | -- Compresses the given uncompressed string. |
36 | -- Unless the uncompressed string starts with "\002", this is guaranteed to return a string equal to or smaller than |
37 | -- the passed string. |
38 | -- the returned string will only contain "\000" characters in rare circumstances, and will contain none if the |
39 | -- source string has none. |
40 | --@param uncompressed |
41 | local dict = {}
|
42 | local function CompressLZW(uncompressed) |
43 | if type(uncompressed) == "string" then |
44 | local dict_size = 256 |
45 | for k in pairs(dict) do |
46 | dict[k] = nil |
47 | end |
48 | local result = {"\002"}
|
49 | local w = '' |
50 | local ressize = 1 |
51 | for i = 0, 255 do |
52 | dict[string_char(i)] = i |
53 | end |
54 | for i = 1, #uncompressed do |
55 | local c = uncompressed:sub(i,i) |
56 | local wc = w..c |
57 | if dict[wc] then |
58 | w = wc |
59 | else |
60 | dict[wc] = dict_size |
61 | dict_size = dict_size +1 |
62 | local r = encode(dict[w]) |
63 | ressize = ressize + #r |
64 | result[#result + 1] = r |
65 | w = c |
66 | end |
67 | end |
68 | if w then |
69 | local r = encode(dict[w]) |
70 | ressize = ressize + #r |
71 | result[#result + 1] = r |
72 | end |
73 | print("uc="..tostring(#uncompressed)..", ressize="..tostring(ressize))
|
74 | if (#uncompressed+1) > ressize then |
75 | return table_concat(result) |
76 | else |
77 | return string_char(1)..uncompressed |
78 | end |
79 | else |
80 | return nil, "Can only compress strings" |
81 | end |
82 | end |
83 | |
84 | solution = CompressLZW |
from http://code.google.com/p/eoi/source/browse/trunk/LibCompress.lua hmm! doesn't seem to compress much. strings like "hello hello hello ..." stay the same. endless repetitions of one character do get compressed when you put in enough of them.
test run test run with input download show line numbers
Travelled to 12 computer(s): aoiabmzegqzx, bhatertpkbcr, cbybwowwnfue, gwrvuhgaqvyk, ishqpsrjomds, lpdgvwnxivlt, mqqgnosmbjvj, pyentgdyhuwx, pzhvpgtvlbxg, tslmcundralx, tvejysmllsmz, vouqrxazstgt
No comments. add comment
| Recognizer | Recognition Result | Visualize | Recalc |
|---|---|---|---|
| #308 | 3112 | [visualize] |
| Snippet ID: | #75 |
| Snippet name: | LZW compressor |
| Eternal ID of this version: | #75/1 |
| Text MD5: | b47c1c6300cc75cde87eeb38e7a07fe4 |
| Author: | stefan |
| Category: | compressors |
| Type: | Lua code |
| Public (visible to everyone): | Yes |
| Archived (hidden from active list): | No |
| Created/modified: | 2014-01-02 04:06:07 |
| Source code size: | 3112 bytes / 84 lines |
| Pitched / IR pitched: | Yes / Yes |
| Views / Downloads: | 1700 / 364 |
| Referenced in: | [show references] |