Revive the threshold for Metal FP32 mish

ChinChangYang · ChinChangYang · commit eda158f6f086 · 2025-04-08T08:45:43.000+08:00
diff --git a/cpp/neuralnet/metalbackend.swift b/cpp/neuralnet/metalbackend.swift
@@ -80,11 +80,17 @@ extension MPSGraph {
         assert(tensor.dataType == .float32)
 
         let one = 1.0
+        let threshold = 10.39
+        let thresholdTensor = constant(threshold, dataType: tensor.dataType)
+        let minimumTensor = minimum(tensor, thresholdTensor, name: nil)
+        let expTensor = exponent(with: minimumTensor, name: nil)
         let oneTensor = constant(one, dataType: tensor.dataType)
-        let expTensor = exponent(with: tensor, name: nil)
         let addTensor = addition(expTensor, oneTensor, name: nil)
         let logTensor = logarithm(with: addTensor, name: nil)
-        let tanhTensor = tanh(with: logTensor, name: nil)
+        let lessTensor = lessThan(tensor, thresholdTensor, name: nil)
+        let selectTensor = select(
+            predicate: lessTensor, trueTensor: logTensor, falseTensor: tensor, name: nil)
+        let tanhTensor = tanh(with: selectTensor, name: nil)
         let mulTensor = multiplication(tensor, tanhTensor, name: nil)
 
         return mulTensor
