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OC-KittenOS/com2/bdivide.lua

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