On Thursday, December 8, 2016 5:41:02 PM PST Haixia Shi 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. > > v2: added more explanation in the comment. > v3: fixed a typo in the comment. > > 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 | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/src/compiler/glsl/builtin_functions.cpp > b/src/compiler/glsl/builtin_functions.cpp > index 3e4bcbb..0bacffb 100644 > --- a/src/compiler/glsl/builtin_functions.cpp > +++ b/src/compiler/glsl/builtin_functions.cpp > @@ -3563,9 +3563,18 @@ builtin_builder::_tanh(const glsl_type *type) > ir_variable *x = in_var(type, "x"); > MAKE_SIG(type, v130, 1, x); > > + /*
For future reference, /* doesn't go on its own line in Mesa. (We can fix that when pushing, no big deal.) Thanks for fixing this. The explanation makes sense. Reviewed-by: Kenneth Graunke <kenn...@whitecape.org> > + * Clamp x to [-10, +10] to avoid precision problems. > + * 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. > + */ > + 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; > } >
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