[Mesa-dev] [PATCH v2 09/53] compiler/spirv: implement 16-bit hyperbolic trigonometric functions

[Jason Ekstrand]

On Wed, Dec 19, 2018 at 5:51 AM Iago Toral Quiroga <itoral at igalia.com>
wrote:

> v2:
>  - use nir_fadd_imm and nir_fmul_imm helpers (Jason)
> ---
>  src/compiler/spirv/vtn_glsl450.c | 44 +++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 18 deletions(-)
>
> diff --git a/src/compiler/spirv/vtn_glsl450.c
> b/src/compiler/spirv/vtn_glsl450.c
> index ec91d9308c5..c8400d6c80f 100644
> --- a/src/compiler/spirv/vtn_glsl450.c
> +++ b/src/compiler/spirv/vtn_glsl450.c
> @@ -654,17 +654,17 @@ handle_glsl450_alu(struct vtn_builder *b, enum
> GLSLstd450 entrypoint,
>     case GLSLstd450Sinh:
>        /* 0.5 * (e^x - e^(-x)) */
>        val->ssa->def =
> -         nir_fmul(nb, nir_imm_float(nb, 0.5f),
> -                      nir_fsub(nb, build_exp(nb, src[0]),
> -                                   build_exp(nb, nir_fneg(nb, src[0]))));
> +         nir_fmul_imm(nb, nir_fsub(nb, build_exp(nb, src[0]),
> +                                       build_exp(nb, nir_fneg(nb,
> src[0]))),
> +                          0.5f);
>        return;
>
>     case GLSLstd450Cosh:
>        /* 0.5 * (e^x + e^(-x)) */
>        val->ssa->def =
> -         nir_fmul(nb, nir_imm_float(nb, 0.5f),
> -                      nir_fadd(nb, build_exp(nb, src[0]),
> -                                   build_exp(nb, nir_fneg(nb, src[0]))));
> +         nir_fmul_imm(nb, nir_fadd(nb, build_exp(nb, src[0]),
> +                                       build_exp(nb, nir_fneg(nb,
> src[0]))),
> +                          0.5f);
>        return;
>
>     case GLSLstd450Tanh: {
> @@ -675,30 +675,38 @@ handle_glsl450_alu(struct vtn_builder *b, enum
> GLSLstd450 entrypoint,
>         * We clamp x to (-inf, +10] to avoid precision problems.  When x >
> 10,
>         * e^2x is so much larger than 1.0 that 1.0 gets flushed to zero in
> the
>         * computation e^2x +/- 1 so it can be ignored.
> +       *
> +       * For 16-bit precision we clamp x to (-inf, +4.2] since the maximum
> +       * representable number is only 65,504 and e^(2*6) exceeds that.
> Also,
> +       * if x > 4.2, tanh(x) will return 1.0 in fp16.
>         */
> -      nir_ssa_def *x = nir_fmin(nb, src[0], nir_imm_float(nb, 10));
> -      nir_ssa_def *exp2x = build_exp(nb, nir_fmul(nb, x,
> nir_imm_float(nb, 2)));
> -      val->ssa->def = nir_fdiv(nb, nir_fsub(nb, exp2x, nir_imm_float(nb,
> 1)),
> -                                   nir_fadd(nb, exp2x, nir_imm_float(nb,
> 1)));
> +      const uint32_t bit_size = src[0]->bit_size;
> +      const double clamped_x = bit_size > 16 ? 10.0 : 4.2;
> +      nir_ssa_def *x = nir_fmin(nb, src[0],
> +                                    nir_imm_floatN_t(nb, clamped_x,
> bit_size));
> +      nir_ssa_def *exp2x = build_exp(nb, nir_fmul_imm(nb, x, 2.0));
> +      val->ssa->def = nir_fdiv(nb, nir_fadd_imm(nb, exp2x, -1.0),
> +                                   nir_fadd_imm(nb, exp2x, 1.0));
>        return;
>     }
>
>     case GLSLstd450Asinh:
>        val->ssa->def = nir_fmul(nb, nir_fsign(nb, src[0]),
>           build_log(nb, nir_fadd(nb, nir_fabs(nb, src[0]),
> -                       nir_fsqrt(nb, nir_fadd(nb, nir_fmul(nb, src[0],
> src[0]),
> -                                                  nir_imm_float(nb,
> 1.0f))))));
> +                       nir_fsqrt(nb, nir_fadd_imm(nb, nir_fmul(nb,
> src[0], src[0]),
> +                                                      1.0f)))));
>        return;
>     case GLSLstd450Acosh:
>        val->ssa->def = build_log(nb, nir_fadd(nb, src[0],
> -         nir_fsqrt(nb, nir_fsub(nb, nir_fmul(nb, src[0], src[0]),
> -                                    nir_imm_float(nb, 1.0f)))));
> +         nir_fsqrt(nb, nir_fadd_imm(nb, nir_fmul(nb, src[0], src[0]),
> +                                        -1.0f))));
>        return;
>     case GLSLstd450Atanh: {
> -      nir_ssa_def *one = nir_imm_float(nb, 1.0);
> -      val->ssa->def = nir_fmul(nb, nir_imm_float(nb, 0.5f),
> -         build_log(nb, nir_fdiv(nb, nir_fadd(nb, one, src[0]),
> -                                    nir_fsub(nb, one, src[0]))));
> +      nir_ssa_def *one = nir_imm_floatN_t(nb, 1.0, src[0]->bit_size);
> +      val->ssa->def =
> +         nir_fmul_imm(nb, build_log(nb, nir_fdiv(nb, nir_fadd_imm(nb,
> src[0], 1.0f),
>

Since you had to declare one for the line below, you could just use it
here.  Doesn't really matter though.


> +                                        nir_fsub(nb, one, src[0]))),
> +                          0.5f);
>        return;
>     }
>
> --
> 2.17.1
>
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