Re: Lua 5.4.2 New assorted suggestions

[Sean Conner <sean@...>]

It was thus said that the Great Sean Conner once stated:
> 
>   And if string comparisons are of such performance important, you might as
> well skip strncmp() entirely (which still has to check for a NUL byte
> anyway) and use a straight memcmp():
> 
> 	if (strcmp(fname, "-") == 0 && memcmp(argv[-1], "--",2) != 0)

  Okay, three things wrong here---first off, I'm failed to include the
trailing NUL byte.  Second, I missed a strcmp()

	if (memcmp(fname,"-",2) == 0 && memcmp(argv[-1],"--",3) != 0)

  Third thing, this is *still* wrong in general.  Let's take an earlier
example:

	if (strcmp(ar.namewhat, "method") == 0) {

  If this is changed to memcmp(), as I suggested:

	if (memcmp(ar.namewhat,"method",7) == 0) {

If ar.namewhat is shorter than 7 characters (including the NUL byte) then
you run the risk of reading unknown memory, which invokes undefined behavior
in C.  I mean, it'll *probably* be okay in practice, but valgrind would
complain bitterly about reading uninitialized memory when testing.  You
still need to check for a NUL byte on both strings.

  So I rescind my recommendation to use memcmp().  I mean, I got *three*
things wrong in the span of *one* line of C code.  There's a reason the code
is written the way it is.

  -spc