diff options
| author | Jason Ekstrand <[email protected]> | 2016-12-09 09:34:50 -0800 |
|---|---|---|
| committer | Jason Ekstrand <[email protected]> | 2016-12-09 18:38:21 -0800 |
| commit | da1c49171d0df185545cfbbd600e287f7c6160fa (patch) | |
| tree | f344d29affe732755dc68fdca2d06676e0e566e4 | |
| parent | 9807f502eb7a023be619a14119388b2a43271b0e (diff) | |
spirv: Use a simpler and more correct implementaiton of tanh()
The new implementation is more correct because it clamps the incoming value
to 10 to avoid floating-point overflow. It also uses a much reduced
version of the formula which only requires 1 exp() rather than 2. This
fixes all of the dEQP-VK.glsl.builtin.precision.tanh.* tests.
Reviewed-by: Kenneth Graunke <[email protected]>
Cc: "13.0" <[email protected]>
| -rw-r--r-- | src/compiler/spirv/vtn_glsl450.c | 23 |
1 files changed, 14 insertions, 9 deletions
diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_glsl450.c index cb0570d385f..fbc7ce6fd84 100644 --- a/src/compiler/spirv/vtn_glsl450.c +++ b/src/compiler/spirv/vtn_glsl450.c @@ -565,16 +565,21 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint, build_exp(nb, nir_fneg(nb, src[0])))); return; - case GLSLstd450Tanh: - /* (0.5 * (e^x - e^(-x))) / (0.5 * (e^x + e^(-x))) */ - val->ssa->def = - nir_fdiv(nb, 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(nb, nir_imm_float(nb, 0.5f), - nir_fadd(nb, build_exp(nb, src[0]), - build_exp(nb, nir_fneg(nb, src[0]))))); + case GLSLstd450Tanh: { + /* tanh(x) := (0.5 * (e^x - e^(-x))) / (0.5 * (e^x + e^(-x))) + * + * With a little algebra this reduces to (e^2x - 1) / (e^2x + 1) + * + * 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. + */ + 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))); return; + } case GLSLstd450Asinh: val->ssa->def = nir_fmul(nb, nir_fsign(nb, src[0]), |