On Thu, Dec 8, 2016 at 5:03 PM, Haixia Shi <h...@chromium.org> wrote:
> Clamp input scalar value to range [-10, +10] to avoid precision problems > when the absolute value of input is too large. > > Fixes dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.* > test > failures. > > Signed-off-by: Haixia Shi <h...@chromium.org> > Cc: Jason Ekstrand <ja...@jlekstrand.net>, > Cc: Stéphane Marchesin <marc...@chromium.org>, > Cc: Kenneth Graunke <kenn...@whitecape.org> > > Change-Id: I324c948b3323ff8107127c42934f14459e124b95 > --- > src/compiler/glsl/builtin_functions.cpp | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/src/compiler/glsl/builtin_functions.cpp > b/src/compiler/glsl/builtin_functions.cpp > index 3e4bcbb..4ede925 100644 > --- a/src/compiler/glsl/builtin_functions.cpp > +++ b/src/compiler/glsl/builtin_functions.cpp > @@ -3563,9 +3563,13 @@ builtin_builder::_tanh(const glsl_type *type) > ir_variable *x = in_var(type, "x"); > MAKE_SIG(type, v130, 1, x); > > + /* clamp x to [-10, +10] to avoid precision problems */ > Would you mind adding something like this to your comment: When x > 10, e^-x is so small relative to e^x that it gets flushed to zero in the computation e^x + e^-x. The same happens in the other direction when x < -10. With that added, Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net> Chatting with Ken a bit, I realized why you used 20 before. That's the threshold needed if you're doing the computation in double-precision. However, GLSL doesn't define a double form of tanh so that's not really a problem. > + ir_variable *t = body.make_temp(type, "tmp"); > + body.emit(assign(t, min2(max2(x, imm(-10.0f)), imm(10.0f)))); > + > /* (e^x - e^(-x)) / (e^x + e^(-x)) */ > - body.emit(ret(div(sub(exp(x), exp(neg(x))), > - add(exp(x), exp(neg(x)))))); > + body.emit(ret(div(sub(exp(t), exp(neg(t))), > + add(exp(t), exp(neg(t)))))); > > return sig; > } > -- > 2.8.0.rc3.226.g39d4020 > >
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