124 lines
3.6 KiB
Lua
124 lines
3.6 KiB
Lua
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--[[----------------------------------------------------------------------------
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LZSS - encoder / decoder
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This is free and unencumbered software released into the public domain.
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Anyone is free to copy, modify, publish, use, compile, sell, or
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distribute this software, either in source code form or as a compiled
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binary, for any purpose, commercial or non-commercial, and by any
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means.
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In jurisdictions that recognize copyright laws, the author or authors
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of this software dedicate any and all copyright interest in the
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software to the public domain. We make this dedication for the benefit
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of the public at large and to the detriment of our heirs and
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successors. We intend this dedication to be an overt act of
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relinquishment in perpetuity of all present and future rights to this
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software under copyright law.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
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OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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OTHER DEALINGS IN THE SOFTWARE.
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For more information, please refer to <http://unlicense.org/>
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--]]----------------------------------------------------------------------------
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--------------------------------------------------------------------------------
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local M = {}
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local string, table = string, table
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--------------------------------------------------------------------------------
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local POS_BITS = 12
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local LEN_BITS = 16 - POS_BITS
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local POS_SIZE = 1 << POS_BITS
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local LEN_SIZE = 1 << LEN_BITS
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local LEN_MIN = 3
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--------------------------------------------------------------------------------
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function M.compress(input)
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local offset, output = 1, {}
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local window = ''
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local function search()
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for i = LEN_SIZE + LEN_MIN - 1, LEN_MIN, -1 do
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local str = string.sub(input, offset, offset + i - 1)
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local pos = string.find(window, str, 1, true)
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if pos then
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return pos, str
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end
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end
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end
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while offset <= #input do
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local flags, buffer = 0, {}
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for i = 0, 7 do
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if offset <= #input then
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local pos, str = search()
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if pos and #str >= LEN_MIN then
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local tmp = ((pos - 1) << LEN_BITS) | (#str - LEN_MIN)
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buffer[#buffer + 1] = string.pack('>I2', tmp)
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else
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flags = flags | (1 << i)
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str = string.sub(input, offset, offset)
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buffer[#buffer + 1] = str
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end
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window = string.sub(window .. str, -POS_SIZE)
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offset = offset + #str
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else
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break
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end
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end
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if #buffer > 0 then
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output[#output + 1] = string.char(flags)
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output[#output + 1] = table.concat(buffer)
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end
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end
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return table.concat(output)
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end
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--------------------------------------------------------------------------------
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function M.decompress(input)
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local offset, output = 1, {}
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local window = ''
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while offset <= #input do
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local flags = string.byte(input, offset)
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offset = offset + 1
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for i = 1, 8 do
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local str = nil
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if (flags & 1) ~= 0 then
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if offset <= #input then
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str = string.sub(input, offset, offset)
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offset = offset + 1
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end
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else
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if offset + 1 <= #input then
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local tmp = string.unpack('>I2', input, offset)
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offset = offset + 2
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local pos = (tmp >> LEN_BITS) + 1
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local len = (tmp & (LEN_SIZE - 1)) + LEN_MIN
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str = string.sub(window, pos, pos + len - 1)
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end
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end
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flags = flags >> 1
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if str then
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output[#output + 1] = str
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window = string.sub(window .. str, -POS_SIZE)
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end
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end
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end
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return table.concat(output)
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end
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return M
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