On Fri, 2016-04-22 at 15:06 -0700, Jason Ekstrand wrote:
> Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net>
>
>
> Did the v2 fix anything other than newly added tests?
No, only the new tests that targeted the cases where the unbiased
exponent was between 0 and 52.
Iago
> --Jason
>
>
> On Thu, Apr 21, 2016 at 10:13 PM, Samuel Iglesias Gonsálvez
> <sigles...@igalia.com> wrote:
> From: Iago Toral Quiroga <ito...@igalia.com>
>
> At least i965 hardware does not have native support for
> truncating doubles.
>
> v2:
> - Simplified the implementation significantly.
> - Fixed the else branch, that was not doing what we wanted.
> ---
> src/compiler/nir/nir.h | 1 +
> src/compiler/nir/nir_lower_double_ops.c | 60
> +++++++++++++++++++++++++++++++++
> 2 files changed, 61 insertions(+)
>
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 9bfb24a..ab8ae99 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2330,6 +2330,7 @@ typedef enum {
> nir_lower_drcp = (1 << 0),
> nir_lower_dsqrt = (1 << 1),
> nir_lower_drsq = (1 << 2),
> + nir_lower_dtrunc = (1 << 3),
> } 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 e22e822..e8ae884 100644
> --- a/src/compiler/nir/nir_lower_double_ops.c
> +++ b/src/compiler/nir/nir_lower_double_ops.c
> @@ -299,6 +299,58 @@ lower_sqrt_rsq(nir_builder *b,
> nir_ssa_def *src, bool sqrt)
> return res;
> }
>
> +static nir_ssa_def *
> +lower_trunc(nir_builder *b, nir_ssa_def *src)
> +{
> + nir_ssa_def *unbiased_exp = nir_isub(b, get_exponent(b,
> src),
> + nir_imm_int(b,
> 1023));
> +
> + nir_ssa_def *frac_bits = nir_isub(b, nir_imm_int(b, 52),
> unbiased_exp);
> +
> + /*
> + * Decide the operation to apply depending on the unbiased
> exponent:
> + *
> + * if (unbiased_exp < 0)
> + * return 0
> + * else if (unbiased_exp > 52)
> + * return src
> + * else
> + * return src & (~0 << frac_bits)
> + *
> + * Notice that the else branch is a 64-bit integer
> operation that we need
> + * to implement in terms of 32-bit integer arithmetics (at
> least until we
> + * support 64-bit integer arithmetics).
> + */
> +
> + /* Compute "~0 << frac_bits" in terms of hi/lo 32-bit
> integer math */
> + nir_ssa_def *mask_lo =
> + nir_bcsel(b,
> + nir_ige(b, frac_bits, nir_imm_int(b, 32)),
> + nir_imm_int(b, 0),
> + nir_ishl(b, nir_imm_int(b, ~0), frac_bits));
> +
> + nir_ssa_def *mask_hi =
> + nir_bcsel(b,
> + nir_ilt(b, frac_bits, nir_imm_int(b, 33)),
> + nir_imm_int(b, ~0),
> + nir_ishl(b,
> + nir_imm_int(b, ~0),
> + nir_isub(b, frac_bits,
> nir_imm_int(b, 32))));
> +
> + nir_ssa_def *src_lo = nir_unpack_double_2x32_split_x(b,
> src);
> + nir_ssa_def *src_hi = nir_unpack_double_2x32_split_y(b,
> src);
> +
> + return
> + nir_bcsel(b,
> + nir_ilt(b, unbiased_exp, nir_imm_int(b, 0)),
> + nir_imm_double(b, 0.0),
> + nir_bcsel(b, nir_ige(b, unbiased_exp,
> nir_imm_int(b, 53)),
> + src,
> + nir_pack_double_2x32_split(b,
> +
> nir_iand(b, mask_lo, src_lo),
> +
> nir_iand(b, mask_hi, src_hi))));
> +}
> +
> static void
> lower_doubles_instr(nir_alu_instr *instr,
> nir_lower_doubles_options options)
> {
> @@ -322,6 +374,11 @@ lower_doubles_instr(nir_alu_instr *instr,
> nir_lower_doubles_options options)
> return;
> break;
>
> + case nir_op_ftrunc:
> + if (!(options & nir_lower_dtrunc))
> + return;
> + break;
> +
> default:
> return;
> }
> @@ -345,6 +402,9 @@ lower_doubles_instr(nir_alu_instr *instr,
> nir_lower_doubles_options options)
> case nir_op_frsq:
> result = lower_sqrt_rsq(&bld, src, false);
> break;
> + case nir_op_ftrunc:
> + result = lower_trunc(&bld, src);
> + break;
> default:
> unreachable("unhandled opcode");
> }
> --
> 2.5.0
>
>
>
>
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