refactor softplus fn

src/llama-model.cpp

@@ -19181,16 +19181,10 @@ private:
 
         GGML_ASSERT(ggml_nelements(beta) + ggml_nelements(alpha) == ggml_nelements(mixed_ba));
 
-        // Softplus would be nice...
+        ggml_tensor * alpha_softplus = softplus(alpha, model.layers[il].ssm_dt);
-        ggml_tensor * alpha_biased = ggml_add(ctx0, alpha, model.layers[il].ssm_dt);  // a + dt_bias
-        ggml_tensor * alpha_exp    = ggml_exp(ctx0, alpha_biased);                    // exp(a + dt_bias)
-        ggml_tensor * one_tensor   = ggml_new_tensor_1d(ctx0, GGML_TYPE_F32, 1);      // Create scalar tensor
-        ggml_exp(ctx0, one_tensor);                                                   // make it a 1
-        ggml_tensor * one_plus_exp   = ggml_add1(ctx0, alpha_exp, one_tensor);        // 1 + exp(a + dt_bias)
-        ggml_tensor * alpha_softplus = ggml_log(ctx0, one_plus_exp);                  // log(1 + exp(...))
         ggml_tensor * A_log_exp      = ggml_exp(ctx0, model.layers[il].ssm_a);        // A_log.exp()
         ggml_tensor * gate_scaled    = ggml_mul(ctx0, alpha_softplus, A_log_exp);     // A_log.exp() * softplus
-        ggml_tensor * gate           = ggml_neg(ctx0, gate_scaled);                   // - (A_log.exp() * softplus)
+        ggml_tensor * gate           = ggml_scale(ctx0, gate_scaled, -1.0f);          // - (A_log.exp() * softplus)
 
         // Get convolution weights and bias
         ggml_tensor * conv_weight = model.layers[il].ssm_conv1d;
@@ -19324,6 +19318,14 @@ private:
 
         return cur;
     }
+
+    ggml_tensor * softplus(ggml_tensor * alpha, ggml_tensor * dt_bias) {
+        ggml_tensor * alpha_biased   = ggml_add(ctx0, alpha, dt_bias);                // a + dt_bias
+        ggml_tensor * alpha_exp      = ggml_exp(ctx0, alpha_biased);                  // exp(a + dt_bias)
+        ggml_tensor * one_plus_exp   = ggml_scale_bias(ctx0, alpha_exp, 1.0f, 1.0f);  // 1 + exp(a + dt_bias)
+        ggml_tensor * alpha_softplus = ggml_log(ctx0, one_plus_exp);                  // log(1 + exp(...))
+        return alpha_softplus;
+    }
 };