softmax(): use std::max_element (#20306)

selfdrive/modeld/models/commonmodel.cc

@@ -1,5 +1,6 @@
 #include <assert.h>
 #include <math.h>
+#include <algorithm>
 #include "commonmodel.h"
 #include "common/clutil.h"
 #include "common/mat.h"
@@ -48,18 +49,10 @@ void frame_free(ModelFrame* frame) {
 }
 
 void softmax(const float* input, float* output, size_t len) {
-  float max_val = -FLT_MAX;
+  const float max_val = *std::max_element(input, input + len);
-  for(int i = 0; i < len; i++) {
-    const float v = input[i];
-    if( v > max_val ) {
-      max_val = v;
-    }
-  }
-
   float denominator = 0;
   for(int i = 0; i < len; i++) {
-    float const v = input[i];
+    float const v_exp = expf(input[i] - max_val);
-    float const v_exp = expf(v - max_val);
     denominator += v_exp;
     output[i] = v_exp;
   }
@@ -68,7 +61,6 @@ void softmax(const float* input, float* output, size_t len) {
   for(int i = 0; i < len; i++) {
     output[i] *= inv_denominator;
   }
-
 }
 
 float sigmoid(float input) {