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https://github.com/kepler155c/opus
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cleanup
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kepler155c@gmail.com
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sys/lzwfs.lua
250
sys/lzwfs.lua
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-- see: https://github.com/Rochet2/lualzw
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-- MIT License - Copyright (c) 2016 Rochet2
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-- Transparent file system compression for non-binary files using lzw
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-- Files that are compressed will have the first bytes in file set to 'LZWC'.
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-- If a file does not benefit from compression, the contents will not be altered.
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-- Allow exclusions for files that shouldn't be compressed
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-- Also allow for future types of exclusions using bit operations
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-- 1 is reserved for compression exclusion
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-- fs.addException('startup.lua', 1)
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-- To renable compression for a file
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-- fs.removeException('startup.lua', 1)
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-- Restores file system
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-- fs.restore()
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local char = string.char
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local type = type
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local sub = string.sub
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local tconcat = table.concat
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local tinsert = table.insert
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local bit = _G.bit
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local fs = _G.fs
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local SIGC = 'LZWC'
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local IGNORE_COMPRESSION = 1 -- support other bits as well
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local basedictcompress = {}
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local basedictdecompress = {}
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for i = 0, 255 do
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local ic, iic = char(i), char(i, 0)
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basedictcompress[ic] = iic
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basedictdecompress[iic] = ic
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end
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local native = { open = fs.open }
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fs.exceptions = fs.exceptions or { }
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local function dictAddA(str, dict, a, b)
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if a >= 256 then
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a, b = 0, b+1
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if b >= 256 then
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dict = {}
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b = 1
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end
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end
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dict[str] = char(a,b)
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a = a+1
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return dict, a, b
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end
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local function compress(input)
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if type(input) ~= "string" then
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error ("string expected, got "..type(input))
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end
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local len = #input
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if len <= 1 then
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return input
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end
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local dict = {}
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local a, b = 0, 1
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local result = { SIGC }
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local resultlen = 1
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local n = 2
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local word = ""
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for i = 1, len do
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local c = sub(input, i, i)
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local wc = word..c
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if not (basedictcompress[wc] or dict[wc]) then
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local write = basedictcompress[word] or dict[word]
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if not write then
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error "algorithm error, could not fetch word"
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end
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result[n] = write
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resultlen = resultlen + #write
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n = n+1
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if len <= resultlen then
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return input
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end
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dict, a, b = dictAddA(wc, dict, a, b)
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word = c
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else
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word = wc
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end
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end
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result[n] = basedictcompress[word] or dict[word]
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resultlen = resultlen+#result[n]
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if len <= resultlen then
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return input
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end
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return tconcat(result)
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end
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local function dictAddB(str, dict, a, b)
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if a >= 256 then
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a, b = 0, b+1
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if b >= 256 then
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dict = {}
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b = 1
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end
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end
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dict[char(a,b)] = str
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a = a+1
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return dict, a, b
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end
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local function decompress(input)
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if type(input) ~= "string" then
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error( "string expected, got "..type(input))
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end
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if #input <= 1 then
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return input
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end
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local control = sub(input, 1, 4)
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if control ~= SIGC then
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return input
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end
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input = sub(input, 5)
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local len = #input
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if len < 2 then
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error("invalid input - not a compressed string")
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end
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local dict = {}
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local a, b = 0, 1
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local result = {}
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local n = 1
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local last = sub(input, 1, 2)
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result[n] = basedictdecompress[last] or dict[last]
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n = n+1
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for i = 3, len, 2 do
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local code = sub(input, i, i+1)
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local lastStr = basedictdecompress[last] or dict[last]
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if not lastStr then
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error( "could not find last from dict. Invalid input?")
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end
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local toAdd = basedictdecompress[code] or dict[code]
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if toAdd then
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result[n] = toAdd
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n = n+1
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dict, a, b = dictAddB(lastStr..sub(toAdd, 1, 1), dict, a, b)
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else
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local tmp = lastStr..sub(lastStr, 1, 1)
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result[n] = tmp
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n = n+1
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dict, a, b = dictAddB(tmp, dict, a, b)
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end
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last = code
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end
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return tconcat(result)
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end
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local function split(str, pattern)
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pattern = pattern or "(.-)\n"
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local t = {}
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local function helper(line) tinsert(t, line) return "" end
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helper((str:gsub(pattern, helper)))
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return t
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end
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function fs.open(fname, flags)
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if flags == 'r' then
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local f, err = native.open(fname, 'rb')
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if not f then
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return f, err
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end
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local ctr = 0
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local lines
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return {
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readLine = function()
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if not lines then
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lines = split(decompress(f.readAll()))
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end
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ctr = ctr + 1
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return lines[ctr]
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end,
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readAll = function()
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return decompress(f.readAll())
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end,
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close = function()
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f.close()
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end,
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}
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elseif flags == 'w' or flags == 'a' then
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if bit.band(fs.exceptions[fs.combine(fname, '')] or 0, IGNORE_COMPRESSION) == IGNORE_COMPRESSION then
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return native.open(fname, flags)
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end
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local c = { }
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if flags == 'a' then
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local f = fs.open(fname, 'r')
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if f then
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tinsert(c, f.readAll())
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f.close()
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end
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end
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local f, err = native.open(fname, 'wb')
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if not f then
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return f, err
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end
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return {
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write = function(str)
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tinsert(c, str)
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end,
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writeLine = function(str)
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tinsert(c, str)
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tinsert(c, '\n')
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end,
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flush = function()
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-- this isn't gonna work...
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-- f.write(compress(tconcat(c)))
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f.flush();
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end,
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close = function()
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f.write(compress(tconcat(c)))
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f.close()
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end,
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}
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end
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return native.open(fname, flags)
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end
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function fs.addException(fname, mode)
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fname = fs.combine(fname, '')
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fs.exceptions[fname] = bit.bor(fs.exceptions[fname] or 0, mode)
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end
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function fs.removeException(fname, mode)
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fname = fs.combine(fname, '')
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fs.exceptions[fname] = bit.bxor(fs.exceptions[fname] or 0, mode)
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end
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function fs.restore()
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fs.open = native.open
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end
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