From: Dmitry Kurtaev <dmitry.kurtaev+github@gmail.com>
Date: Mon, 22 Jun 2020 20:22:21 +0000 (+0300)
Subject: Optimize Mish for CPU backend
X-Git-Tag: submit/tizen/20210224.033012~2^2~142^2~10^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=1491934d17e582378272dfdbdee00dc0ea5faa86;p=platform%2Fupstream%2Fopencv.git

Optimize Mish for CPU backend
---

diff --git a/modules/dnn/src/layers/elementwise_layers.cpp b/modules/dnn/src/layers/elementwise_layers.cpp
index 776053e..1bd8abe 100644
--- a/modules/dnn/src/layers/elementwise_layers.cpp
+++ b/modules/dnn/src/layers/elementwise_layers.cpp
@@ -667,8 +667,11 @@ struct MishFunctor : public BaseFunctor
         {
             for( int i = 0; i < len; i++ )
             {
+                // Use fast approximation introduced in https://github.com/opencv/opencv/pull/17200
                 float x = srcptr[i];
-                dstptr[i] = x * tanh(log(1.0f + exp(x)));
+                float eX = exp(std::min(x, 20.f));
+                float n = (eX + 2) * eX;
+                dstptr[i] = (x * n) / (n + 2);
             }
         }
     }