Small optimization (5% core utilization drop)

mryndzionek · Aug 24, 2024 · 2c2406d · 2c2406d
1 parent 3bee999
commit 2c2406d
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diff --git a/README.md b/README.md
@@ -76,7 +76,7 @@ in frames, nine frames a second.
 ![sharnn](https://github.com/mryndzionek/esp32s3_eye_kws_demo/blob/main/images/sharnn.png)
 
 The core utilization is ~70%.
-Core1 every 105ms does NN inference which takes about 90ms (80% core utilization).
+Core1 every 105ms does NN inference which takes about 85ms (77% core utilization).
 
 The microphone (INMP441) connections are as follows:
 

diff --git a/src/fast_grnn.c b/src/fast_grnn.c
@@ -26,16 +26,16 @@ const float INPUT_STDEVS[32] =
 
 // clang-format on
 
-static inline float sigmoidf(float n)
+static inline float sigmoidf(float x)
 {
-    return (1 / (1 + powf(EULER_NUMBER_F, -n)));
+    return (tanhf(x / 2.0f) + 1.0f) / 2.0f;
 }
 
 static inline float expo(float y)
 {
     if (y > 80)
         y = 80;
-    return exp(y);
+    return expf(y);
 }
 
 static float softmax(const float *xs, size_t n, size_t len)