Rotation (sort of)

[Phantom]

[Dan East]

[Dan East]

[Kak]

[Phantom]

[Kak]

[refractor]

[Andy]

[Kzinti]

[Andy]

[Tala]

[fdave]

[Phantom]

Dave,

Correct me if I'm wrong, but I think your formula is not correct. If I feed it x=30, y=2, I get:

((2-30+16)&31)-16 = (-12&31)-16, which equals -4.

For x=2, y=30 I get:

((30-2+16)&31)-16 = (44&31)-16, which equals -4 (should have been 4).

This could probably be corrected by xor'ing the sign bit of the (x+y+16) part. That's pretty much what refractor does. Great solution! Mind if I use it in a game? I'm glad my instincts where right: It's branchless...

Tala: Also correct me if I'm wrong, but if x=30 and y=2, your formula gives -28 (should have been 4).

- Jacco.

[Digby]

Hi Jacco,

I'm curious, how many times are you calling this function per frame? If you're going to the trouble to worry about branches, is this bit of code a currently a bottleneck in your game?

For sake of discussion, let's say this code executed in one cycle - how much faster would it allow your game to run compared to the original implementation posted at the beginning of this thread? Would the user even notice it?

[refractor]