Fix incorrect model prediction for binary TF and CART models without …

…features.

The error was spotted in: tensorflow/decision-forests#188
Fixed #188

PiperOrigin-RevId: 556206372

yggdrasil_decision_forests/serving/decision_forest/decision_forest_serving.cc

@@ -179,19 +179,20 @@ inline void PredictHelper(
   utils::usage::OnInference(num_examples, model.metadata);
   const int num_features = model.features().fixed_length_features().size();
   predictions->resize(num_examples);
+  const typename Model::ValueType* sample = examples.data();
   for (int example_idx = 0; example_idx < num_examples; ++example_idx) {
     float output = 0.f;
-    if (num_features > 0) {
-      const auto* sample = &examples[example_idx * num_features];
-      for (const auto root_node_idx : model.root_offsets) {
-        const auto* node = &model.nodes[root_node_idx];
-        while (node->right_idx) {
-          node += EvalCondition(node, sample) ? node->right_idx : 1;
-        }
-        output += node->label;
+
+    for (const auto root_node_idx : model.root_offsets) {
+      const auto* node = &model.nodes[root_node_idx];
+      while (node->right_idx) {
+        node += EvalCondition(node, sample) ? node->right_idx : 1;
       }
+      output += node->label;
     }
+
     (*predictions)[example_idx] = FinalTransform(model, output);
+    sample += num_features;
   }
 }
 
@@ -301,7 +302,7 @@ inline void PredictHelperOptimizedV1(
 
   // Select the first example.
   // Note: The examples are stored example-major/feature-minor.
-  const typename Model::ValueType* sample = &examples[0];
+  const typename Model::ValueType* sample = examples.data();
   for (size_t example_idx = 0; example_idx < num_examples; ++example_idx) {
     // Accumulator of the predictions for the current example.
     float output = 0.f;