Re: Table (sequence) concatenation

[Hisham <h@...>]

On 23 January 2015 at 13:44, Soni L. <fakedme@gmail.com> wrote:
> How can I quickly concatenate 2 tables? (or convert a whole string to a
> table of bytes/numbers)
>
> For example:
>
> local t = {string.byte(str, 1, stack_limit)} .. {string.byte(str,
> stack_limit+1, stack_limit*2)} -- .. etc
>
> Or:
>
> local t = string.bytearray(str)
>
> Both of them would be much faster (and human-friendly) than this:
>
> local t1 = {string.byte(str, 1, stack_limit)}
> local t2 = {string.byte(str, stack_limit+1, stack_limit*2)}
> local t = t1
> for k,v in ipairs(t2) do
>   t[k+stack_limit] = v
> end
> -- etc

--os.execute("dd if=/dev/urandom of=file bs=1M count=1")
local fd = io.open("file")
local longstr = fd:read("*a")
fd:close()

-- time: about 0.17 on Lua 5.2
-- time: about 0.19 on Lua 5.3
-- time: about 0.02 on LuaJIT
local function strarray(longstr)
    local t = {}
    for i = 1, #longstr do
       t[i] = longstr:byte(i)
    end
    return t
end

-- time: about 0.11 on Lua 5.3
-- time: about 0.11 on Lua 5.2 + compat53
-- time: about 0.08 on LuaJIT + compat53
local function strarray2(longstr)
    -- tuning the step does not affect speed much
    -- (for this example size, at least.)
    local step = 500
    local t = {}
    for i = 1, #longstr, step do
       local u = { longstr:byte(i, i+step) }
       table.move(u, 1, #u, i, t)
    end
    return t
end

-- time: about 0.11 on Lua 5.2
-- time: about 0.14 on Lua 5.3
-- time: about 0.03 on LuaJIT
local function strarray3(longstr)
    local step = 500
    local t = {}
    for i = 1, #longstr, step do
       local u = { longstr:byte(i, i+step) }
       for m = 1, #u do
           t[i+m-1] = u[m]
       end
    end
    return t
end

local function dump(t)
    for i = 1, #t, 16 do
        for x = 0, 15 do
           io.write( ("%02x "):format(t[i+x]) )
        end
        io.write("\n")
    end
end

local function check(t1, t2)
    if #t1 ~= #t2 then return false end
    for i = 1, #t1 do
       if t1[i] ~= t2[i] then return false end
    end
    return true
end

local t = strarray(longstr)
--local t2 = strarray2(longstr)
--local t3 = strarray3(longstr)
--print(check(t, t3))
--dump(t)