<div dir="ltr"><div><div>Matt, </div>Care to take this one? I'm not that familiar with roundeven. </div>--Jason </div><div class="gmail_extra"> <div class="gmail_quote">On Tue, Apr 12, 2016 at 1:05 AM, Samuel Iglesias Gonsálvez <<a href="mailto:siglesias@igalia.com" target="_blank">siglesias@igalia.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">From: Iago Toral Quiroga <<a href="mailto:itoral@igalia.com">itoral@igalia.com</a>> At least i965 hardware does not have native support for round_even() on doubles. --- src/compiler/nir/nir.h | 3 +- src/compiler/nir/nir_lower_double_ops.c | 58 +++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+), 1 deletion(-) diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h index 4a57e74..0d17ce0 100644 --- a/src/compiler/nir/nir.h +++ b/src/compiler/nir/nir.h @@ -2289,7 +2289,8 @@ typedef enum { nir_lower_dtrunc = (1 << 3), nir_lower_dfloor = (1 << 4), nir_lower_dceil = (1 << 5), - nir_lower_dfract = (1 << 6) + nir_lower_dfract = (1 << 6), + nir_lower_dround_even = (1 << 7) } nir_lower_doubles_options; void nir_lower_doubles(nir_shader *shader, nir_lower_doubles_options options); diff --git a/src/compiler/nir/nir_lower_double_ops.c b/src/compiler/nir/nir_lower_double_ops.c index 0f42c21..3d98075 100644 --- a/src/compiler/nir/nir_lower_double_ops.c +++ b/src/compiler/nir/nir_lower_double_ops.c @@ -423,6 +423,55 @@ lower_fract(nir_builder *b, nir_ssa_def *src) return nir_fsub(b, src, nir_ffloor(b, src)); } +static nir_ssa_def * +lower_round_even(nir_builder *b, nir_ssa_def *src) +{ + /* If fract(src) == 0.5, then we will have to decide the rounding direction. + * We will do this by computing the mod(abs(src), 2) and testing if it + * is < 1 or not. + * + * We compute mod(abs(src), 2) as: + * abs(src) - 2.0 * floor(abs(src) / 2.0) + */ + nir_ssa_def *two = nir_imm_double(b, 2.0); + nir_ssa_def *abs_src = nir_fabs(b, src); + nir_ssa_def *mod = + nir_fsub(b, + abs_src, + nir_fmul(b, + two, + nir_ffloor(b, + nir_fmul(b, + abs_src, + nir_imm_double(b, 0.5))))); + + /* + * If fract(src) != 0.5, then we round as floor(src + 0.5) + * + * If fract(src) == 0.5, then we have to check the modulo: + * + * if it is < 1 we need a trunc operation so we get: + * 0.5 -> 0, -0.5 -> -0 + * 2.5 -> 2, -2.5 -> -2 + * + * otherwise we need to check if src >= 0, in which case we need to round + * upwards, or not, in which case we need to round downwards so we get: + * 1.5 -> 2, -1.5 -> -2 + * 3.5 -> 4, -3.5 -> -4 + */ + nir_ssa_def *fract = nir_ffract(b, src); + return nir_bcsel(b, + nir_fne(b, fract, nir_imm_double(b, 0.5)), + nir_ffloor(b, nir_fadd(b, src, nir_imm_double(b, 0.5))), + nir_bcsel(b, + nir_flt(b, mod, nir_imm_double(b, 1.0)), + nir_ftrunc(b, src), + nir_bcsel(b, + nir_fge(b, src, nir_imm_double(b, 0.0)), + nir_fadd(b, src, nir_imm_double(b, 0.5)), + nir_fsub(b, src, nir_imm_double(b, 0.5))))); +} + static void lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options) { @@ -466,6 +515,11 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options) return; break; + case nir_op_fround_even: + if (!(options & nir_lower_dround_even)) + return; + break; + default: return; } @@ -501,6 +555,10 @@ lower_doubles_instr(nir_alu_instr *instr, nir_lower_doubles_options options) case nir_op_ffract: result = lower_fract(&bld, src); break; + case nir_op_fround_even: + result = lower_round_even(&bld, src); + break; + default: unreachable("unhandled opcode"); } -- 2.5.0 _______________________________________________ mesa-dev mailing list <a href="mailto:mesa-dev@lists.freedesktop.org">mesa-dev@lists.freedesktop.org</a> <a href="https://lists.freedesktop.org/mailman/listinfo/mesa-dev" rel="noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/mesa-dev</a> </blockquote></div> </div>