Matt,
Care to take this one? I'm not that familiar with roundeven.
--Jason
On Tue, Apr 12, 2016 at 1:05 AM, Samuel Iglesias Gonsálvez <
sigles...@igalia.com> wrote:
> From: Iago Toral Quiroga <ito...@igalia.com>
>
> 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
>
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