Re: help optimizing a small lua function implemented in a C module.

[Sean Conner <sean@...>]

It was thus said that the Great Emmanuel Oga once stated:
> Hi, I implemented my very first C module for a lua program, be nice :-).
> 
> Without further ado:
> 
> https://gist.github.com/938457
> 
> There is a bench program and a test one in case you feel like meddling
> with the code. 

  What should

	subsequence.subsequenceMatch("banunus","as") 

  return?

  Because as is, the code is returning "true".  I'm not sure if this is
intended or not.  Other observations about the code:

1. luaL_checklstring() will never return NULL.  So you can remove 
	if (pattern && str)

2. You already bound pidx to 0, so it will always be >= 0, so you can change

	if (pidx >= 0 && pidx < lpat)

  with

	if (pidx < lpat)

3. I tend to like early returns; if you do this, any time you assign 1 to
found you can replace it with:

	lua_pushboolean(L,1);
	return 1;

  Then the end of the function:

	if (found) {
	  lua_pushboolean(L,1)
	} else {
	  lua_pushnumber(L,(lua_Number)pidx + 1);
	}

	return 1;

  can now be:

	lua_pushnumber(L,pidx + 1);
	return 1;

(I can tell you are using a C++ compiler for this, as the C++ style comments
are not strictly legal in C89; also, C++ compilers force one to cast; the
casts here are not strictly necessary in C89)

> I'm pretty happy with the 24x speed up for lua and 8x speed up for
> luajit but since I'm running the function over thousands of strings
> I'm wondering if a little more speed could be squeezed on the C side.

  Even with the changes I've made, they didn't show much of an improvement
in speed.  But depending upon your answer to my question above, there may be
a way to improve the speed.

  -spc