Looks good to me, albeit it's potentially minimally slower, so I'm wondering if the higher precision is actually useful? I guess though the last two steps could use lp_build_fmuladd? Reviewed-by: Roland Scheidegger <srol...@vmware.com>
Am 25.06.19 um 11:17 schrieb Jose Fonseca: > Use the alternative more accurate expression from > https://en.wikipedia.org/wiki/Division_algorithm#Newton%E2%80%93Raphson_division > > Tested by enabling this code path, and running gloss mesa demo. > --- > src/gallium/auxiliary/gallivm/lp_bld_arit.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c > b/src/gallium/auxiliary/gallivm/lp_bld_arit.c > index 02fb81afe51..8aa5931eb69 100644 > --- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c > +++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c > @@ -2707,11 +2707,11 @@ lp_build_sqrt(struct lp_build_context *bld, > /** > * Do one Newton-Raphson step to improve reciprocate precision: > * > - * x_{i+1} = x_i * (2 - a * x_i) > + * x_{i+1} = x_i + x_i * (1 - a * x_i) > * > * XXX: Unfortunately this won't give IEEE-754 conformant results for 0 or > * +/-Inf, giving NaN instead. Certain applications rely on this behavior, > - * such as Google Earth, which does RCP(RSQRT(0.0) when drawing the Earth's > + * such as Google Earth, which does RCP(RSQRT(0.0)) when drawing the Earth's > * halo. It would be necessary to clamp the argument to prevent this. > * > * See also: > @@ -2724,12 +2724,13 @@ lp_build_rcp_refine(struct lp_build_context *bld, > LLVMValueRef rcp_a) > { > LLVMBuilderRef builder = bld->gallivm->builder; > - LLVMValueRef two = lp_build_const_vec(bld->gallivm, bld->type, 2.0); > LLVMValueRef res; > > res = LLVMBuildFMul(builder, a, rcp_a, ""); > - res = LLVMBuildFSub(builder, two, res, ""); > + res = LLVMBuildFSub(builder, bld->one, res, ""); > + > res = LLVMBuildFMul(builder, rcp_a, res, ""); > + res = LLVMBuildFAdd(builder, rcp_a, res, ""); > > return res; > } > _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
