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| author | Kristian H. Kristensen <hoegsberg@google.com> | 2020-02-26 16:52:45 -0800 |
|---|---|---|
| committer | Eric Engestrom <eric@engestrom.ch> | 2020-03-06 22:59:42 +0100 |
| commit | fa1d2996f70929f962f0a0498ceb088b0a2fcdf2 (patch) | |
| tree | 8644100c22b1288e7085846a62c7a3be14b49c52 | |
| parent | dba2d46d8c059d29d65b0fc43b0ce777620e5929 (diff) | |
| download | mesa-fa1d2996f70929f962f0a0498ceb088b0a2fcdf2.tar.gz | |
Revert "glsl: Use a simpler formula for tanh"
This reverts commit 9807f502eb7a023be619a14119388b2a43271b0e.
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>
(cherry picked from commit 986e92f0ea803caf014adc40e900bc774af71da3)
| -rw-r--r-- | .pick_status.json | 2 | ||||
| -rw-r--r-- | src/compiler/glsl/builtin_functions.cpp | 18 |
2 files changed, 9 insertions, 11 deletions
diff --git a/.pick_status.json b/.pick_status.json index 0a80b02cbf6..ee733be8156 100644 --- a/.pick_status.json +++ b/.pick_status.json @@ -697,7 +697,7 @@ "description": "Revert \"glsl: Use a simpler formula for tanh\"", "nominated": true, "nomination_type": 2, - "resolution": 0, + "resolution": 1, "master_sha": null, "because_sha": "9807f502eb7a023be619a14119388b2a43271b0e" }, diff --git a/src/compiler/glsl/builtin_functions.cpp b/src/compiler/glsl/builtin_functions.cpp index e262a1ec780..cfb9607698a 100644 --- a/src/compiler/glsl/builtin_functions.cpp +++ b/src/compiler/glsl/builtin_functions.cpp @@ -4928,19 +4928,17 @@ 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; } |