Re: Most efficient way to recognize a line by its first (up to) three characters

[Shmuel Zeigerman <shmuz@...>]

On 11/03/2014 19:25, meino.cramer@gmx.de wrote:
> Hi,
>
> (using Lua 5.2.2 under Linux)
>
> from a serial line I receive A LOT of lines
> consisting of data in ASCII format.
>
> The first one to three characters decide, how
> I have to interpret the data.
> Since data are transmitted FAST I want to make
> the recognition code which branches into the
> different data processing parts as efficient
> as possible. The code will run on a embedded
> system, so I will not have the memory for huge
> look-up table or such...
> And I will do it in pure Lua since this is the
> reason why I do this in pure Lua! ;)
>
> What is the "best" solution?
> ('best' in "" since this also a product of the
> point of view ;)

For simplicity sake, let it always be 3 characters to decide.
Define as many 3-character identifiers as you need.
Then it is a simple if-else:

    local prefix, info = line:sub(1,3), line:sub(4)
    if prefix == "abc" then
      -- do something
    elseif prefix == "123" then
      -- do something else
    elseif ...

(Strings equality test is very cheap in Lua.)

--
Shmuel