28-Feb-2013 20:52, Walter Bright пишет:
On 2/28/2013 3:29 AM, Jonathan M Davis wrote:
And you were just claiming that the lexer checked the sentinel type in
only
one place. If that's indeed the case (and I think that it's quite
close to
being true if it isn't true), then you _wouldn't_ need to use static
ifs like
this in many places. So, which is it? If you need to check the
sentinel often
enough that using static ifs is a problem, then it's probably not
buying you
much of anything over checking empty anyway.
Please, again, examine lexer.c.
For example, look at what happens after line 719. Try 794 in particular.
Now look at line 996 and what follows. Note that there is not a single
null check there, yet the code is correct and does not run off the end
of the data.
But my point is that outside of strings or arrays, you're almost
certainly
stuck with that.
I've given you two examples (lexer and regexp) where you are certainly
not stuck with that, and those two cases matter.
I'll add that when I wrote current std.regex internal VM I've switched
to the sentinel as terminator of the program instead of checking the
length. The end result was about 5% of speed up gained back then
(measured on DMD alone though, other compilers didn't compile it at the
time).
In the lexer it may help a bit more given the lookahead.
--
Dmitry Olshansky
