92 lines
2.2 KiB
Lua
92 lines
2.2 KiB
Lua
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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EXPORT.lzss = M |