Am 13.10.2015 um 01:01 schrieb Matt Turner: > On Mon, Oct 12, 2015 at 3:07 PM, Roland Scheidegger <srol...@vmware.com> > wrote: >> As far as I can tell (and I could easily be wrong here...) intel hw >> doesn't have explicit conversion instruction, you just say it's a f16 >> destination. As such I believe the conversion used would just use >> ordinary rounding mode, which is of course usually round to nearest even >> (and the docs don't seem to mention it, but seems likely that too large >> floats would get converted to infinities using that mode). Rounding mode >> is of course changeable (but would need to change it back after f32->f16 >> mov). > > There's F32TO16/F16TO32 in Gen7 (IVB, HSW, VLV). The software routines > were modified to match their behavior for constant propagation, as far > as I know. >
Yes, I was looking at Broadwell, which can do the implicit conversion. Regardless, I guess it works the same for both wrt rounding - you'd have to change the rounding mode if you want round-to-zero as d3d10 requires (I suspect that's exactly what the d3d driver does, since d3d11 f32tof16 instruction requires that too). Otherwise it's just round-to-nearest-even which will round too large numbers to infinity. (Albeit the docs don't quite seem to explicitly say default rounding mode affects the half-float result of the f32tof16 instruction.) But for GL any rounding is fine of course, and matching hw probably makes sense. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
