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kepler155c@gmail.com 2019-11-05 11:18:21 -07:00
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sys/lzwfs.lua
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-- see: https://github.com/Rochet2/lualzw
-- MIT License - Copyright (c) 2016 Rochet2
-- Transparent file system compression for non-binary files using lzw
-- Files that are compressed will have the first bytes in file set to 'LZWC'.
-- If a file does not benefit from compression, the contents will not be altered.
-- Allow exclusions for files that shouldn't be compressed
-- Also allow for future types of exclusions using bit operations
-- 1 is reserved for compression exclusion
-- fs.addException('startup.lua', 1)
-- To renable compression for a file
-- fs.removeException('startup.lua', 1)
-- Restores file system
-- fs.restore()
local char = string.char
local type = type
local sub = string.sub
local tconcat = table.concat
local tinsert = table.insert
local bit = _G.bit
local fs = _G.fs
local SIGC = 'LZWC'
local IGNORE_COMPRESSION = 1 -- support other bits as well
local basedictcompress = {}
local basedictdecompress = {}
for i = 0, 255 do
local ic, iic = char(i), char(i, 0)
basedictcompress[ic] = iic
basedictdecompress[iic] = ic
end
local native = { open = fs.open }
fs.exceptions = fs.exceptions or { }
local function dictAddA(str, dict, a, b)
if a >= 256 then
a, b = 0, b+1
if b >= 256 then
dict = {}
b = 1
end
end
dict[str] = char(a,b)
a = a+1
return dict, a, b
end
local function compress(input)
if type(input) ~= "string" then
error ("string expected, got "..type(input))
end
local len = #input
if len <= 1 then
return input
end
local dict = {}
local a, b = 0, 1
local result = { SIGC }
local resultlen = 1
local n = 2
local word = ""
for i = 1, len do
local c = sub(input, i, i)
local wc = word..c
if not (basedictcompress[wc] or dict[wc]) then
local write = basedictcompress[word] or dict[word]
if not write then
error "algorithm error, could not fetch word"
end
result[n] = write
resultlen = resultlen + #write
n = n+1
if len <= resultlen then
return input
end
dict, a, b = dictAddA(wc, dict, a, b)
word = c
else
word = wc
end
end
result[n] = basedictcompress[word] or dict[word]
resultlen = resultlen+#result[n]
if len <= resultlen then
return input
end
return tconcat(result)
end
local function dictAddB(str, dict, a, b)
if a >= 256 then
a, b = 0, b+1
if b >= 256 then
dict = {}
b = 1
end
end
dict[char(a,b)] = str
a = a+1
return dict, a, b
end
local function decompress(input)
if type(input) ~= "string" then
error( "string expected, got "..type(input))
end
if #input <= 1 then
return input
end
local control = sub(input, 1, 4)
if control ~= SIGC then
return input
end
input = sub(input, 5)
local len = #input
if len < 2 then
error("invalid input - not a compressed string")
end
local dict = {}
local a, b = 0, 1
local result = {}
local n = 1
local last = sub(input, 1, 2)
result[n] = basedictdecompress[last] or dict[last]
n = n+1
for i = 3, len, 2 do
local code = sub(input, i, i+1)
local lastStr = basedictdecompress[last] or dict[last]
if not lastStr then
error( "could not find last from dict. Invalid input?")
end
local toAdd = basedictdecompress[code] or dict[code]
if toAdd then
result[n] = toAdd
n = n+1
dict, a, b = dictAddB(lastStr..sub(toAdd, 1, 1), dict, a, b)
else
local tmp = lastStr..sub(lastStr, 1, 1)
result[n] = tmp
n = n+1
dict, a, b = dictAddB(tmp, dict, a, b)
end
last = code
end
return tconcat(result)
end
local function split(str, pattern)
pattern = pattern or "(.-)\n"
local t = {}
local function helper(line) tinsert(t, line) return "" end
helper((str:gsub(pattern, helper)))
return t
end
function fs.open(fname, flags)
if flags == 'r' then
local f, err = native.open(fname, 'rb')
if not f then
return f, err
end
local ctr = 0
local lines
return {
readLine = function()
if not lines then
lines = split(decompress(f.readAll()))
end
ctr = ctr + 1
return lines[ctr]
end,
readAll = function()
return decompress(f.readAll())
end,
close = function()
f.close()
end,
}
elseif flags == 'w' or flags == 'a' then
if bit.band(fs.exceptions[fs.combine(fname, '')] or 0, IGNORE_COMPRESSION) == IGNORE_COMPRESSION then
return native.open(fname, flags)
end
local c = { }
if flags == 'a' then
local f = fs.open(fname, 'r')
if f then
tinsert(c, f.readAll())
f.close()
end
end
local f, err = native.open(fname, 'wb')
if not f then
return f, err
end
return {
write = function(str)
tinsert(c, str)
end,
writeLine = function(str)
tinsert(c, str)
tinsert(c, '\n')
end,
flush = function()
-- this isn't gonna work...
-- f.write(compress(tconcat(c)))
f.flush();
end,
close = function()
f.write(compress(tconcat(c)))
f.close()
end,
}
end
return native.open(fname, flags)
end
function fs.addException(fname, mode)
fname = fs.combine(fname, '')
fs.exceptions[fname] = bit.bor(fs.exceptions[fname] or 0, mode)
end
function fs.removeException(fname, mode)
fname = fs.combine(fname, '')
fs.exceptions[fname] = bit.bxor(fs.exceptions[fname] or 0, mode)
end
function fs.restore()
fs.open = native.open
end