KonstantinSeurer
/
mesa
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Revert "glsl: Use a simpler formula for tanh" 

This reverts commit 9807f502eb.

The simplified formula doesn't pass the tanh dEQP tests when we lower
to fp16 math.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4054>
This commit is contained in:
Kristian H. Kristensen 2020-02-26 16:52:45 -08:00 committed by Marge Bot
parent bc5724faf4
commit 986e92f0ea
1 changed files with 8 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
src/compiler/glsl/builtin_functions.cpp
View File

@ -5169,19 +5169,17 @@ builtin_builder::_tanh(const glsl_type *type)
ir_variable *x = in_var(type, "x");
MAKE_SIG(type, v130, 1, x);
/* 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)
*
* 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.
/* 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(x, imm(10.0f))));
body.emit(assign(t, min2(max2(x, imm(-10.0f)), imm(10.0f))));
body.emit(ret(div(sub(exp(mul(t, imm(2.0f))), imm(1.0f)),
add(exp(mul(t, imm(2.0f))), imm(1.0f)))));
/* (e^x - e^(-x)) / (e^x + e^(-x)) */
body.emit(ret(div(sub(exp(t), exp(neg(t))),
add(exp(t), exp(neg(t))))));
return sig;
}