Floor and Ceil versus Denormals on CPU and GPU
27 points
4 days ago
| 3 comments
| asawicki.info
| HN
yosefk
14 minutes ago
[-]
Flush denormals to zero. Even their inventor had trouble writing correct code in their presence - see the Appendix to that "what every programmer should know..." paper
reply
kevmo314
41 minutes ago
[-]
> This is not the first time we can see Nvidia taking shortcuts to achieve maximum performance of their GPUs

Why is implementing it correctly not performant? For context I have no idea how rounding is typically implemented anyways.

reply
crote
2 hours ago
[-]
Another thing to keep in mind is that CPU processing of denormals tends to be extremely slow - I vaguely recall running into something like a 10x slowdown a decade ago.

For a lot of applications the difference between a denormal and zero is small enough to be irrelevant, so if you expect near-zero values to be common, enabling a denormals-to-zero compiler flag might give you a pretty nice performance boost for free.

reply