Am 18.11.2014 um 15:05 schrieb Ilia Mirkin: > On Tue, Nov 18, 2014 at 8:54 AM, Roland Scheidegger <srol...@vmware.com> > wrote: >> Am 18.11.2014 um 05:03 schrieb Ilia Mirkin: >>> For values above integer accuracy in floats, val - floor(val) might >>> actually produce a value greater than 1. For such large floats, it's >>> reasonable to be imprecise, but it's unreasonable for FRC to return a >>> value that is not between 0 and 1. >>> >>> Signed-off-by: Ilia Mirkin <imir...@alum.mit.edu> >>> --- >>> src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp >>> b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp >>> index 41b91e8..e5b767f 100644 >>> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp >>> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp >>> @@ -2512,7 +2512,8 @@ Converter::handleInstruction(const struct >>> tgsi_full_instruction *insn) >>> src0 = fetchSrc(0, c); >>> val0 = getScratch(); >>> mkOp1(OP_FLOOR, TYPE_F32, val0, src0); >>> - mkOp2(OP_SUB, TYPE_F32, dst0[c], src0, val0); >>> + mkOp2(OP_SUB, TYPE_F32, val0, src0, val0); >>> + mkOp1(OP_SAT, TYPE_F32, dst0[c], val0); >>> } >>> break; >>> case TGSI_OPCODE_ROUND: >>> >> >> I don't understand the math behind this. For any such large number, as >> far as I can tell floor(val) == val and hence the end result ought to be >> zero. Or doesn't your floor work like that? > > I could be thinking about this backwards, but let's say that floats > lose integer precision at 10.0. And I do floor(12.5)... normally this > would be 12.0, but since that's not exactly representable, it might > actually be 11.0. (Or would it be 11.9987? I didn't consider that > possibility...) And then 12.5 - 11 = 1.5. Or am I thinking about this > backwards? I guess ideally I'd do something along the lines of y = x - > floor(x); return y - floor(y). That seems like it might be more > accurate... not sure. > If your float is large enough that the next closest float is more than 1.0 away, then that float would have been an exact integer, thus floor() doing nothing.
Roland _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
