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Struct = {}
function Struct.pack(format, ...)
local stream = {}
local vars = {...}
local endianness = true
for i = 1, format:len() do
local opt = format:sub(i, i)
if opt == '>' then
endianness = false
elseif opt:find('[bBhHiIlL]') then
local n = opt:find('[hH]') and 2 or opt:find('[iI]') and 4 or opt:find('[lL]') and 8 or 1
local val = tonumber(table.remove(vars, 1))
if val < 0 then
val = val + 2 ^ (n * 8 - 1)
end
local bytes = {}
for j = 1, n do
table.insert(bytes, string.char(val % (2 ^ 8)))
val = math.floor(val / (2 ^ 8))
end
if not endianness then
table.insert(stream, string.reverse(table.concat(bytes)))
else
table.insert(stream, table.concat(bytes))
end
elseif opt:find('[fd]') then
local val = tonumber(table.remove(vars, 1))
local sign = 0
if val < 0 then
sign = 1
val = -val
end
local mantissa, exponent = math.frexp(val)
if val == 0 then
mantissa = 0
exponent = 0
else
mantissa = (mantissa * 2 - 1) * math.ldexp(0.5, (opt == 'd') and 53 or 24)
exponent = exponent + ((opt == 'd') and 1022 or 126)
end
local bytes = {}
if opt == 'd' then
val = mantissa
for i = 1, 6 do
table.insert(bytes, string.char(math.floor(val) % (2 ^ 8)))
val = math.floor(val / (2 ^ 8))
end
else
table.insert(bytes, string.char(math.floor(mantissa) % (2 ^ 8)))
val = math.floor(mantissa / (2 ^ 8))
table.insert(bytes, string.char(math.floor(val) % (2 ^ 8)))
val = math.floor(val / (2 ^ 8))
end
table.insert(bytes, string.char(math.floor(exponent * ((opt == 'd') and 16 or 128) + val) % (2 ^ 8)))
val = math.floor((exponent * ((opt == 'd') and 16 or 128) + val) / (2 ^ 8))
table.insert(bytes, string.char(math.floor(sign * 128 + val) % (2 ^ 8)))
val = math.floor((sign * 128 + val) / (2 ^ 8))
if not endianness then
table.insert(stream, string.reverse(table.concat(bytes)))
else
table.insert(stream, table.concat(bytes))
end
elseif opt == 's' then
table.insert(stream, tostring(table.remove(vars, 1)))
table.insert(stream, string.char(0))
elseif opt == 'c' then
local n = format:sub(i + 1):match('%d+')
local length = tonumber(n)
if length > 0 then
local str = tostring(table.remove(vars, 1))
if length - str:len() > 0 then
str = str .. string.rep(' ', length - str:len())
end
table.insert(stream, str:sub(1, length))
end
i = i + n:len()
end
end
return table.concat(stream)
end
function Struct.unpack(format, stream)
local vars = {}
local iterator = 1
local endianness = true
for i = 1, format:len() do
local opt = format:sub(i, i)
if opt == '>' then
endianness = false
elseif opt:find('[bBhHiIlL]') then
local n = opt:find('[hH]') and 2 or opt:find('[iI]') and 4 or opt:find('[lL]') and 8 or 1
local signed = opt:lower() == opt
local val = 0
for j = 1, n do
local byte = string.byte(stream:sub(iterator, iterator))
if endianness then
val = val + byte * (2 ^ ((j - 1) * 8))
else
val = val + byte * (2 ^ ((n - j) * 8))
end
iterator = iterator + 1
end
if signed then
val = val - 2 ^ (n * 8 - 1)
end
table.insert(vars, val)
elseif opt:find('[fd]') then
local n = (opt == 'd') and 8 or 4
local x = stream:sub(iterator, iterator + n - 1)
iterator = iterator + n
if not endianness then
x = string.reverse(x)
end
local sign = 1
local mantissa = string.byte(x, (opt == 'd') and 7 or 3) % ((opt == 'd') and 16 or 128)
for i = n - 2, 1, -1 do
mantissa = mantissa * (2 ^ 8) + string.byte(x, i)
end
if string.byte(x, n) > 127 then
sign = -1
end
local exponent = (string.byte(x, n) % 128) * ((opt == 'd') and 16 or 2) + math.floor(string.byte(x, n - 1) / ((opt == 'd') and 16 or 128))
if exponent == 0 then
table.insert(vars, 0.0)
else
mantissa = (math.ldexp(mantissa, (opt == 'd') and -52 or -23) + 1) * sign
table.insert(vars, math.ldexp(mantissa, exponent - ((opt == 'd') and 1023 or 127)))
end
elseif opt == 's' then
local bytes = {}
for j = iterator, stream:len() do
if stream:sub(j, j) == string.char(0) then
break
end
table.insert(bytes, stream:sub(j, j))
end
local str = table.concat(bytes)
iterator = iterator + str:len() + 1
table.insert(vars, str)
elseif opt == 'c' then
local n = format:sub(i + 1):match('%d+')
table.insert(vars, stream:sub(iterator, iterator + tonumber(n)))
iterator = iterator + tonumber(n)
i = i + n:len()
end
end
return unpack(vars)
end