From 1491934d17e582378272dfdbdee00dc0ea5faa86 Mon Sep 17 00:00:00 2001
From: Dmitry Kurtaev <dmitry.kurtaev+github@gmail.com>
Date: Mon, 22 Jun 2020 23:22:21 +0300
Subject: [PATCH] Optimize Mish for CPU backend

---
 modules/dnn/src/layers/elementwise_layers.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

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);
             }
         }
     }
-- 
2.7.4