Am 09.11.2017 um 18:58 schrieb Roland Scheidegger: > Am 09.11.2017 um 18:27 schrieb Jan Vesely: >> On Thu, 2017-11-09 at 03:58 +0100, srol...@vmware.com wrote: >>> From: Roland Scheidegger <srol...@vmware.com> >>> >>> r600 used the clamped version for rcp, whereas both evergreen and cayman >>> used the ieee version. I don't know why that discrepancy exists (it does so >>> since day 1) but there does not seem to be a valid reason for this, so make >>> it consistent. This seems now safer than before the previous commit (using >>> the mystery dx10 clamp). >>> Note that rsq still uses clamped version (as before even though the table >>> may have suggested otherwise for evergreen) for r600/eg, but not for cayman. >> >> just layman's opinion here. Does TGSI not mandate specific behaviour >> wrt nans and infinities for this OP? > No, not really. Ideally all (non-legacy such as LIT) opcodes would > follow ieee754 (or d3d10) semantics (and that's how they are implemented > at least in llvmpipe). But we don't enforce denorm behavior for instance > neither (llvmpipe will disable them - on x86 at least...). > Some hw supported by gallium drivers also simply can't generate NaNs, no > matter the opcode. > I think in general drivers should try to stick as close to ieee754 (and > d3d10) semantics as they can, regardless what GL may allow, so yes, I > guess the ieee version should be used (albeit the abs modifier doesn't > really fit in there neither, and that is done because there's problems > otherwise). > > Roland > > >> >>> I just don't feel lucky enough to change this (it should also be noted r600 >>> supports sqrt natively, which is always ieee, therefore might not really see >>> rsqrt with glsl often presumably). >> >> why would that be? isn't RECIPSQRT_IEEE(x) still optimization over >> RECIP_IEEE(SQRT(x))?
Forgot to mention previously, I was actually thinking glsl doesn't have rsqrt, but that's not true. In any case, shaders using sqrt will have this lowered to rsqrt/rcp on some drivers, but not r600. I'll send out new patches also rsq to ieee behavior in any case... Roland _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
