Re: finding keys in a table
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- Subject: Re: finding keys in a table
- From: "Alex Davies" <alex.mania@...>
- Date: 2008年2月22日 01:09:21 +0900
Hmmm. I actually meant:
tab[char] = (tab[char] or 0) + 1
Although it shouldn't make any difference.
I'm a bit confused though, because I measured:
for i = 1, 1024*1024*64 do
test.a = (test.a or 0) + 1
end
versus:
for i = 1, 1024*1024*64 do
local count = test.a
if count then
test.a = count + 1
else
test.a = 1
end
end
And on my compiler/computer at least, the top one is consistently faster. No
idea why, given that both give the same opcodes for the main loop:
Gettable, Test, Add, Settable
Of course, if you mean that the first time through the loop would be faster
in the bottom case you would be spot on. Still, if the loop takes any amount
of time, I'd figure the first hit for each letter insignificant. Just an
imo. In any case the top way is a lot neater. =)
Javier: Mike's way is fastest and neatest =)
- Alex
----- Original Message -----
From: "Hans Hagen" <pragma@wxs.nl>
actually,
tab[char] = (count or 0) + 1
is slower than
if count then
tab[char] = count + 1
else
tab[char] = 1
end
(the if then variant takes 60% of the time of the or case; the interpreter
needs an extra LOADK)
in a similar fashion, parallel assignments can be faster
Hans