[speeder]

I stumbled into this bug in a rather spetacular manner.

I was making a game using D3D, Lua and Chipmunk physics, and some of the behaviour of the game was being odd.

So I started to try printing random stuff with Lua, eventually I just tried: print(5+5), and to my surprise my console outputted "11".

I went into Lua's irc channel to talk about this, and everyone said I was nuts, that the number was too small to trigger precision issues, that I was a troll and so on.

After a lot of searching I found out about this D3D bug, so I switched the game to use OpenGL instead there it was, 5+5 = 10 again!

Now why fiddling with the FPU could make 5+5 become 11, I have no idea.

[jcelerier]

If it ends up as 10+epsilon after the loss of precision and for some reason the fp round mode is set to FE_UPWARD ... And some part of the Lua stack recognizes that 5+5 is an integer-yielding expression and casts it as one for the display...