Re: bottleneck: string2hex

[Attila <ejjeliorjarat@...>]

On Sat, 17 Apr 2010 02:39:00 +0300, Valerio Schiavoni
<valerio.schiavoni@gmail.com> wrote:

> Hello,
> profiling my application, the big bottleneck of it comes from this  
> function:
>
> function string2hex(str)
> assert(str,"String2hex got null argument")
>  local h,s =  string.gsub(str, "(.)", function(c) return
> string.format("%02X", string.byte(c)) end)
> return h
> end
>
>
> The size of input strings can be from 1kb to 1Mb.
> How would you optimize it ?
>
>
> thanks for any suggestion,
> valerio

Check p24. in this document: http://www.lua.org/gems/sample.pdf
gsub will create the anonymous function each time it's called. If you put
it outside the block, it'll surely speed up the mechanism:

function string2hex(str)
	assert(str,"String2hex got null argument")
	local hex = function(c) return string.format("%02X", string.byte(c)) end
	local h,s =  string.gsub(str, "(.)", hex)
	return h
end
But Patrick's code snippets might be even better. All in all, it's highly  
recommended to read that book (or at least that part).