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by dahart 1686 days ago
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…
1 comments
a_e_k 1686 days ago
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.

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dahart 1685 days ago
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.

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an1sotropy 1686 days ago
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.

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