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

[Enrico Colombini <erix@...>]

On 11/03/2014 19.13, Luiz Henrique de Figueiredo wrote:
> Consider this scheme instead of a chain of ifs:
>
> local handlers={
> 	["abc"]=function (prefix,info) ... end,
> 	["123"]=function (prefix,info) ... end,
> }
>
> local badprefix=function (prefix,info) error("cannot handle "..prefix) end
>
> while true do
> 	local prefix, info = line:sub(1,3), line:sub(4)
> 	local h = handlers[prefix] or badprefix
> 	h(prefix,info)
> end

In case the embedded system could not tolerate many string allocations, 
an alternative could be to build an integer out of the numeric value of 
the first three characters, such as (untested):

 local a, b, c = string.byte(s, 1, 3)
 local id = (65536 * a) + (256 * b) + c

then use 'id' as index in a table, or for direct comparison.

--
  Enrico