local m = {} -- the module table

local mt = {} -- the module metatable

-- given a binary array, set a metamethod to return its length

-- (e.g., #binaryArray, calls this)

function mt:__len()

return self.size

end

-- Create a new binary array of an initial size

function m.New(sizeOrString)

-- the array storage itself

local o = {}

if type(sizeOrString) == "string" then

o.str = sizeOrString

o.size = #sizeOrString

elseif type(sizeOrString) == "number" then

o.data = {}

o.size = sizeOrString

else

error("Expect a integer size value or string to construct a binary array")

end

-- set the inheritance

setmetatable(o, {__index = mt, __len = mt.__len})

return o

end

-- Get a slice of the binary array from start to end position

function mt:Slice(startPos, endPos)

startPos = startPos or 0

endPos = endPos or self.size

local d = self.data

if d then

-- if the self.data is defined, we are building the buffer

-- in a Lua table

-- new table to store the slice components

local b = {}

-- starting with the startPos, put all

-- values into the new table to be concat later

-- updated the startPos based on the size of the

-- value

while startPos < endPos do

local v = d[startPos] or '/0'

table.insert(b, v)

startPos = startPos + #v

end

-- combine the table of strings into one string

-- this is faster than doing a bunch of concats by themselves

return table.concat(b)

else

-- n.b start/endPos are 0-based incoming, so need to convert

-- correctly. in python a slice includes start -> end - 1

return self.str:sub(startPos+1, endPos)

end

end

-- Grow the binary array to a new size, placing the exisiting data

-- at then end of the new array

function mt:Grow(newsize)

-- the new table to store the data

local newT = {}

-- the offset to be applied to existing entries

local offset = newsize - self.size

-- loop over all the current entries and

-- add them to the new table at the correct

-- offset location

local d = self.data

for i,data in pairs(d) do

newT[i + offset] = data

end

-- update this storage with the new table and size

self.data = newT

self.size = newsize

end

-- memorization for padding strings

local pads = {}

-- pad the binary with n \0 bytes at the starting position

function mt:Pad(n, startPos)

-- use memorization to avoid creating a bunch of strings

-- all the time

local s = pads[n]

if not s then

s = string.rep('\0', n)

pads[n] = s

end

-- store the padding string at the start position in the

-- Lua table

self.data[startPos] = s

end

-- Sets the binary array value at the specified position

function mt:Set(value, position)

self.data[position] = value

end

-- locals for slightly faster access

local sunpack = string.unpack

local spack = string.pack

-- Pack the data into a binary representation

function m.Pack(fmt, ...)

return spack(fmt, ...)

end

-- Unpack the data from a binary representation in

-- a Lua value

function m.Unpack(fmt, s, pos)

return sunpack(fmt, s.str, pos + 1)

end

-- Return the binary array module

return m