Re: Using Lua's string interning for faster compares?
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- Subject: Re: Using Lua's string interning for faster compares?
- From: Philipp Janda <siffiejoe@...>
- Date: 2012年1月18日 07:07:10 +0100
Hi!
On 17.01.2012 08:12, HyperHacker wrote:
When I write modules to wrap C++ objects, they usually have a __index
method that does a lot of string comparing, like:
if(!strcmp(key, "foo")) lua_pushcfunction(L, obj_method_foo);
else if(!strcmp(key, "bar")) lua_pushcfunction(L, obj_method_bar);
etc... I'm not sure if compilers can optimize this, but doing all
those strcmp()s every time a method/field is looked up seems terribly
inefficient.
Try Ragel[1].
[1]: http://www.complang.org/ragel/
I've attached the template I use for such occasions.
HTH,
Philipp
/* This is a template for matching one of multiple strings using the
* ragel state machine compiler. Edit/extend the state machine and the
* defines below. If using more than one state machine in a C file,
* the exported function name must be redefined.
* Compile (to str2id.h):
* $ ragel -C -G2 str2id.rh
* For graphviz output:
* $ ragel -V -p str2id.rh | dot -T png -o out.png
*/
#define STR2ID_FUNC_NAME str2id
#define ID_FOO 0
#define ID_BAR 1
#define ID_BAZ 2
#define ID_FOOBAR 3
#define ID_HELLO 4
#define ID_BYE 5
%%{
machine s2i;
main :=
"foo" %/{ return ID_FOO; } |
"bar" %/{ return ID_BAR; } |
"baz" %/{ return ID_BAZ; } |
"foobar" %/{ return ID_FOOBAR; } |
"hello" %/{ return ID_HELLO; } |
"bye" %/{ return ID_BYE; };
}%%
/* DO NOT CHANGE ANYTHING BELOW THIS COMMENT! */
#include <stddef.h>
static unsigned STR2ID_FUNC_NAME( char const* p, size_t n ) {
char const* pe = p + n;
char const* eof = pe;
int cs = 0;
%%{
write data;
write init;
write exec;
}%%
(void)s2i_en_main;
(void)s2i_error;
(void)s2i_first_final;
return -1;
}
#undef STR2ID_FUNC_NAME