Re: bottleneck: string2hex
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- Subject: Re: bottleneck: string2hex
- From: Sean Conner <sean@...>
- Date: 2010年4月17日 16:44:25 -0400
It was thus said that the Great Florian Weimer once stated:
> * Michal Kottman:
>
> > Another (faster) alternative is to avoid the sprintf() call and
> > calculate hex string directly:
> >
> > static char hex[] = "0123456789ABCDEF";
> >
> > ...
> >
> > for ( p = ns , max = size ; max > 0 ; max--)
> > {
> > *p++ = hex[*s >> 4];
> > *p++ = hex[*s++ & 0xF];
> > }
>
> Caution: this doesn't work with signed chars, you have to change s to
> a pointer to an unsigned char in Sean's code.
Ah, so it won't. Anyway, taking this and the other suggestion to use
lua_newuserdata(), I have this:
/*
* Feel free to use this code
*
* Tested under Linux, your milage may vary
* gcc -Wall -Wextra -pedantic -ansi -g -shared -fpic -o strhex.so strhex.c
*
*/
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
static const char hex[] = "0123456789ABCDEF";
static int strhex(lua_State *L)
{
const unsigned char *s;
size_t size;
size_t max;
char *ns;
char *p;
s = (const unsigned char *)luaL_checklstring(L,1,&size);
ns = lua_newuserdata(L,size * 2);
for ( p = ns , max = size ; max > 0 ; max--)
{
*p++ = hex[*s >> 4];
*p++ = hex[*s++ & 0x0F];
}
lua_pushlstring(L,ns,size * 2);
return 1;
}
int luaopen_strhex(lua_State *L)
{
lua_register(L,"strhex",strhex);
return 0;
}
Old version on my system: 0.66
New version on my system: 0.04
-spc (I should also mention I've been testing with a 2,150,919 byte file)