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Negative zero??

 
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dingo



Joined: 17 Nov 2005
Posts: 2
PostPosted: Thu Nov 17, 2005 6:00 am    Post subject: Negative zero?? Reply with quote
Hello.. First post here.
I noticed an odd bug in luaplayer while working on my complex number calculator. Someone must have surely noticed this, but I've tried searching and I've not found anything.
According to Luaplayer, -1*0 = -0..
Here's the code I've tested it with:
Code:
zero = 0*-1
screen:fillRect(0,0,480,272,Color.new(0,0,0))
screen:print(200,100,tostring(zero),Color.new(255,255,255))
screen:print(200,110,tostring(zero == 0), Color.new(255,255,255))

screen:flip()

while true do
   screen.waitVblankStart()
end


it outputs this:
-0
true

which I guess means -0 has a different value to 0, but is still equal to it.

I'm using user-mode lua (for 2.0 fw) and I've also tested it on the luaplayer for windows alpha.
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Jim



Joined: 02 Jul 2005
Posts: 487
Location: Sydney
PostPosted: Thu Nov 17, 2005 6:51 am    Post subject: Reply with quote
Floating point numbers have both +0 and -0. It's mostly of use to people trying to perform analytical calculations. One example is it can be used to find out if a numerical series converges to 0 and if it approached from above (+0) or below (-0).

It's not a lua bug and you probably shouldn't need to worry about it.

Jim
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dingo



Joined: 17 Nov 2005
Posts: 2
PostPosted: Sat Nov 19, 2005 4:43 am    Post subject: Reply with quote
Ooh OK, thanks for explaining that..
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