Add dfpwm codec implementation

Should match 100% to the Java implementation

Author: gamax92

dfpwm/dfpwm.lua

@@ -0,0 +1,99 @@
+local shell=require("shell")
+
+local args, options=shell.parse(...)
+if options.h or options.help then
+	print([=[Usage: dfpwm [infile [outfile]]
+
+Options:
+	-h --help   This message
+	-d --decode Decode from dfpwm
+	-e --encode Encode to dfpwm (default)
+	-o --old    Use old DFPWM codec
+	-n --new    Use new DFPWM1a codec (default)
+	--bsize=n   Buffer size
+	]=])
+	return
+end
+
+local function errprint(msg)
+	io.stderr:write(msg.."\n")
+	io.stderr:flush()
+end
+
+local encode=true
+local new=true
+local bsize=8192
+
+if options.d or options.decode then
+	encode=false
+end
+if options.o or options.old then
+	new=false
+end
+if options.bsize then
+	bsize=tonumber(options.bsize, 10)
+	if not bsize then
+		errprint("Error: '"..tostring(options.bsize).."' is not a valid number")
+		return
+	end
+end
+
+local dfpwm=require("dfpwm")
+local codec=dfpwm.new(new)
+
+local file, err
+if #args >= 1 then
+	file, err=io.open(args[1], "rb")
+	if not file then
+		errprint(err)
+		return
+	end
+else
+	file=io.stdin
+end
+
+local outfile
+if #args >= 2 then
+	outfile, err=io.open(args[2], "wb")
+	if not outfile then
+		file:close()
+		errprint(err)
+		return
+	end
+else
+	outfile=io.stdout
+end
+
+while true do
+	local data=file:read(bsize)
+	if not data then break end
+	data=table.pack(data:byte(1,-1))
+
+	local odata
+	if encode then
+		for i=1, #data do
+			data[i]=bit32.bxor(data[i], 0x80)
+		end
+		odata=codec:compress(data)
+	else
+		odata=codec:decompress(data)
+		for i=1, #odata do
+			odata[i]=bit32.bxor(odata[i], 0x80)
+		end
+	end
+
+	for i=1, #odata do
+		odata[i]=string.char(odata[i])
+	end
+	outfile:write(table.concat(odata))
+	outfile:flush()
+
+	os.sleep(0)
+end
+
+if #args >= 1 then
+	file:close()
+	if #args >= 2 then
+		outfile:close()
+	end
+end

dfpwm/lib/dfpwm.lua

@@ -0,0 +1,108 @@
+local function ctx_update(state, curbit)
+	local target=(curbit and 127 or -128)
+	local nlevel=state.level+math.floor((state.response*(target-state.level)+state.RESP_PREC_HALF)/state.RESP_PREC_POWER)
+	if nlevel == state.level and state.level ~= target then
+		nlevel=nlevel+(curbit and 1 or -1)
+	end
+
+	local rtarget, rdelta
+	if curbit == state.lastbit then
+		rtarget=state.RESP_PREC_MAX
+		rdelta=state.RESP_INC
+	else
+		rtarget=0
+		rdelta=state.RESP_DEC
+	end
+
+	local nresponse=state.response+(state.new and 0 or math.floor((rdelta*(rtarget-state.response))/256))
+	if nresponse == state.response and state.response ~= rtarget then
+		nresponse=nresponse+((curbit == state.lastbit) and 1 or -1)
+	end
+
+	if state.RESP_PREC > 8 then
+		if nresponse < state.RESP_PREC_8 then
+			nresponse=state.RESP_PREC_8
+		end
+	end
+
+	state.response=nresponse
+	state.lastbit=curbit
+	state.level=nlevel
+end
+
+local function decompress(state, src)
+	local dest={}
+	for i=1, #src do
+		local d=src[i]
+		for j=0, 7 do
+			-- apply context
+			local curbit=(bit32.band(d, bit32.lshift(1, j)) ~= 0)
+			local lastbit=state.lastbit
+			ctx_update(state, curbit)
+			
+			-- apply noise shaping
+			local blevel = bit32.band((curbit == lastbit) and state.level or math.floor((state.flastlevel+state.level+1)/2), 0xFF)
+			if blevel >= 128 then
+				blevel=blevel-256
+			end
+			state.flastlevel=state.level
+
+			-- apply low-pass filter
+			state.lpflevel=state.lpflevel+math.floor((state.LPF_STRENGTH*(blevel-state.lpflevel)+0x80)/256)
+			dest[#dest+1]=bit32.band(state.lpflevel, 0xFF)
+		end
+	end
+	return dest
+end
+
+local function compress(state, src)
+	local dest={}
+	for i=1, #src, 8 do
+		local d=0
+		for j=0, 7 do
+			local inlevel=(src[i+j] or 0)
+			if inlevel >= 128 then
+				inlevel=inlevel-256
+			end
+			local curbit=(inlevel > state.level or (inlevel == state.level and state.level == 127))
+			d=bit32.bor(d/2, curbit and 128 or 0)
+			ctx_update(state, curbit)
+		end
+		dest[#dest+1]=d
+	end
+	return dest
+end
+
+local dfpwm={}
+
+function dfpwm.new(newdfpwm)
+	local state={
+		new=newdfpwm,
+		response=0,
+		level=0,
+		lastbit=false,
+		flastlevel=0,
+		lpflevel=0,
+		decompress=decompress,
+		compress=compress
+	}
+	if newdfpwm then
+		state.RESP_INC=1
+		state.RESP_DEC=1
+		state.RESP_PREC=10
+		state.LPF_STRENGTH=140
+	else
+		state.RESP_INC=7
+		state.RESP_DEC=20
+		state.RESP_PREC=8
+		state.LPF_STRENGTH=100
+	end
+	-- precompute and cache some stuff
+	state.RESP_PREC_HALF=bit32.lshift(1, state.RESP_PREC-1)
+	state.RESP_PREC_POWER=2^state.RESP_PREC
+	state.RESP_PREC_MAX=bit32.lshift(1, state.RESP_PREC)-1
+	state.RESP_PREC_8=bit32.lshift(2, state.RESP_PREC-8)
+	return state
+end
+
+return dfpwm

programs.cfg

@@ -206,4 +206,16 @@
 		authors = "gamax92",
 		repo = "tree/master/ooci"
 	},
+	["dfpwm"] = {
+		files = {
+			["master/dfpwm/lib/dfpwm.lua"] = "/lib",
+			["master/dfpwm/dfpwm.lua"] = "/bin",
+		},
+		dependencies = {
+		},
+		name = "dfpwm codec",
+		description = "Lua implementation of the DFPWM codec",
+		authors = "gamax92, GreaseMonkey (for Java implementation)",
+		repo = "tree/master/dfpwm"
+	},
 }