[dahart]

Knowing said teacher ;) I wonder if he’d still say the same thing now… It’s good practice to have to use single precision (or even half-precision!) now and then in order to be forced to deal with precision issues. Yes, use doubles if you really need them and aren’t trying to learn. But they’re often a lot more than 2x more expensive, and they might not be necessary at all. I’ve heard people who develop commercial rendering software for movies you’ve probably seen say out loud that you never need doubles, you just need to understand how to use floats.

[couchand]

Perhaps you were in the same lecture as me, when I asked the lead developer on Big Hero 6 why they didn't just use doubles to solve their precision woes, and he informed me that they literally couldn't afford to use doubles at that scale.

[dahart]

You know, that is actually ringing a bell, I think I might have indeed. Above I was thinking of someone else who works on a certain renderer made in New Zealand, but it’s true that many studios using doubles either sparingly or not at all. That might be getting even more true as GPUs blend into production…

[a_e_k]

I worked on a certain hopping lamp renderer for more than 11 eleven years. I can confirm that probably 99+% of the floating point math in it was in single precision.

And to this day, typing out the 'f' suffix on single precision literals is muscle memory for me after having had Steven Parker for my Ph.D. advisor.

[dahart]

Is everyone on this thread in Steve’s sphere?? I’m surprised (in a good way) to see so many familiar faces, and I guess a little surprised it’s in a thread about fast-math and not a thread about ray tracing. Okay on second thought it’s not very surprising.

Pixar has told me recently they still use doubles for some things in the CPU side of RenderMan, but I don’t know what for. There are some legitimate cases for it, and occasionally I dip my toes in hot water attempting to give advice to avoid doubles to people who know more than I do about how floats work and why they need doubles.

[an1sotropy]

In the coding framework I created for students we have a "real" typedef that is either for float or double, and with C99's <tgmath.h> you just write "cos" once, and it will turn into cosf or cos depending on how the typedef is set, which allows controlled experimentation on how FP precision affects performance. But for submitted code the grading scripts grep for "double" and turn on various extra warnings to ensure that there are no implicit casts from double to float, in an effort to ensure that single precision is always being used (but I should probably scan the assembly).

Steve Parker was the first person to explain to me (while he was still a student, and I was a much younger one) the sometimes surprising cost of having image sizes be powers of two (because of cache conflicts). Small world.