mirror of https://github.com/20kdc/OC-KittenOS.git
125 lines
2.8 KiB
Lua
125 lines
2.8 KiB
Lua
-- This is released into the public domain.
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-- No warranty is provided, implied or otherwise.
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-- PREPROC (r9 edition): preprocess input to be 7-bit
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local frw = require("libs.frw")
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local
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-- SHARED WITH DECOMPRESSION ENGINE
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function p(x, y)
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if x == 126 then
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return string.char(y), 3
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elseif x == 127 then
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return string.char(128 + y), 3
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elseif x >= 32 then
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return string.char(x), 2
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elseif x == 31 then
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return "\n", 2
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elseif x == 30 then
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return "\x00", 2
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end
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return string.char(("enart"):byte(x % 5 + 1), ("ndtelh"):byte((x - x % 5) / 5 + 1)), 2
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end
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local preprocParts = {}
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local preprocMaxLen = 0
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for i = 0, 127 do
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for j = 0, 127 do
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local d, l = p(i, j)
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if d then
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preprocMaxLen = math.max(preprocMaxLen, #d)
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l = l - 1
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if (not preprocParts[d]) or (#preprocParts[d] > l) then
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if l == 2 then
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preprocParts[d] = string.char(i, j)
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else
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preprocParts[d] = string.char(i)
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end
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end
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end
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end
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end
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local function preproc(blk, p)
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local out = ""
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while blk ~= "" do
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p(blk)
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local len = math.min(preprocMaxLen, #blk)
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while len > 0 do
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local seg = blk:sub(1, len)
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if preprocParts[seg] then
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out = out .. preprocParts[seg]
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blk = blk:sub(#seg + 1)
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break
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end
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len = len - 1
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end
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assert(len ~= 0)
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end
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return out
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end
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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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local function bdivide(blk, p)
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local out = ""
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local windowSize = 0x10000
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local windowData = ("\x00"):rep(windowSize)
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while blk ~= "" do
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p(blk)
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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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out = out .. bestData
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-- crop window
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windowData = (windowData .. bestRes):sub(-windowSize)
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blk = blk:sub(#bestRes + 1)
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end
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return out
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end
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return function (data)
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io.stderr:write("preproc: ")
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local pi = frw.progress()
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local function p(b)
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pi(1 - (#b / #data))
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end
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data = preproc(data, p)
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io.stderr:write("\nbdivide: ")
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pi = frw.progress()
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data = bdivide(data, p)
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io.stderr:write("\n")
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-- These are used to pad the stream to flush the pipeline.
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-- It's cheaper than the required code.
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-- 1 byte of buffer for preproc,
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-- 2 bytes of buffer for bdivide.
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return data .. ("\x00"):rep(3)
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end
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