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eyebex
09-13-2005, 06:42 AM
For a GPGPU application, I'm summing up some floating point numbers (say, in the order of 500 floats) to a render target. What concerns me: On pre-G70 NVIDIA cards (FX4400, FX3400, GF 6800), the results are *exactly* the same. On G70-based cards (7800 GTX, FX 4500) results vary compared to the pre-G70 results in the order of about a tenthousandth part. How can this be? What does the G70 do differently? Which results are to be considered more "correct"?

Thanks for any insights.

Relic
09-13-2005, 06:57 AM
It can be anything, from different precision, rounding, instruction ordering, etc. It's a different hardware after all.
You might want to ask GPGPU specialists on http://www.gpgpu.org/forums/