Re: bottleneck: string2hex
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- Subject: Re: bottleneck: string2hex
- From: Sean Conner <sean@...>
- Date: 2010年4月17日 06:25:32 -0400
It was thus said that the Great Valerio Schiavoni once stated:
> 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 ?
I'd try some Lua variants and if it still proved too slow, I would
probably test a C implementation. Which I did. Test harness:
start = os.clock()
h = string2hex(data)
stop = os.clock()
print("string2hex()",stop - start)
start = os.clock()
h = strhex(data) -- C version
stop = os.clock()
print("strhex()",stop - start)
[spc]lucy:/tmp>lua tlua.lua
string2hex1() 3.52
strhex() 0.65
[spc]lucy:/tmp>
C code is as follows:
/*
* Sample code---feel free to use.
*
* compiled and tested under Linux
* gcc -Wall -Wextra -pedantic -ansi -g -shared -fpic -o strhex.so strhex.c
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
static int strhex(lua_State *L)
{
const char *s;
size_t size;
size_t max;
char *ns;
char *p;
s = luaL_checklstring(L,1,&size);
ns = malloc((size * 2) + 1);
for ( p = ns , max = size ; max > 0 ; max--)
{
sprintf(p,"%02X",*s++);
p += 2;
}
lua_pushlstring(L,ns,size * 2);
free(ns);
return 1;
}
int luaopen_strhex(lua_State *L)
{
lua_register(L,"strhex",strhex);
return 0;
}
Then again, I've been programming in C for years now, so this type of
stuff is second nature to me.
-spc