mirror of https://github.com/20kdc/OC-KittenOS.git
50 lines
1.2 KiB
Lua
50 lines
1.2 KiB
Lua
-- This is released into the public domain.
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-- No warranty is provided, implied or otherwise.
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-- BDIVIDE r5 edition
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-- Algorithm simplified for smaller implementation and potentially better compression
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-- format:
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-- 0-127 for constants
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-- <128 + (length - 4)>, <position high>, <position low>
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-- Position is where in the window it was found, minus 1.
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-- windowSize must be the same between the encoder and decoder,
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-- and is the amount of data preserved after cropping.
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io.write("\x00") -- initiation character
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local blk = io.read("*a")
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local windowSize = 0x10000
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local windowData = ("\x00"):rep(windowSize)
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local function crop(data)
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windowData = (windowData .. data):sub(-windowSize)
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end
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while blk ~= "" do
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local bestData = blk:sub(1, 1)
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local bestRes = bestData
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for lm = 0, 127 do
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local al = lm + 4
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local pfx = blk:sub(1, al)
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if #pfx ~= al then
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break
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end
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local p = windowData:find(pfx, 1, true)
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if not p then
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break
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end
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local pm = p - 1
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local thirdByte = pm % 256
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-- anti ']'-corruption helper
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if thirdByte ~= 93 then
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bestData = string.char(128 + lm, math.floor(pm / 256), thirdByte)
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bestRes = pfx
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end
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end
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-- ok, encode!
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io.write(bestData)
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crop(bestRes)
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blk = blk:sub(#bestRes + 1)
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end
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