Fixed logprobs for greedy. (#886)

Applied LogSoftmax to logits returned by _greedy_sample().
Ticket: CVS-152274

src/cpp/src/logit_processor.hpp

@@ -299,6 +299,20 @@ class PresencePenaltyTransform : public IPenaltyTransformer {
     }
 };
 
+
+class LogFilter : public ILogitTransformer {
+public:
+    LogFilter() {}
+
+    void apply(Logits& logits) override {
+        OPENVINO_ASSERT(logits.is_vector_initialized());
+        for (size_t i = 0; i < logits.m_size; i++) {
+            logits.m_vector[i].m_log_prob = std::log(logits.m_vector[i].m_log_prob);
+        }
+    }
+};
+
+
 } // namespace LogitTransformers
 
 class LogitProcessor {
@@ -352,6 +366,7 @@ class LogitProcessor {
                 if (sampling_params.top_k > 0 && sampling_params.top_k < std::numeric_limits<size_t>::max()) {
                     m_logit_transformers.emplace_back(new LogitTransformers::TopKFilter(sampling_params.top_k));
                 }
+                m_logit_transformers.emplace_back(new LogitTransformers::LogFilter());
             }
         }
     }

src/cpp/src/sampler.hpp

@@ -358,7 +358,15 @@ class Sampler {
                 max_index = i;
             }
         }
-        return Token(logits.m_data[max_index], max_index);
+
+        // apply log softmax to max value
+        float log_sum = std::log(std::accumulate(
+            logits.m_data, logits.m_data + logits.m_size, 0.0f, [max_value](float accumulated, float to_add) {
+                return accumulated + std::exp(to_add - max_value);
+        }));
+        max_value = -log_sum;
+
+        return Token(max_value, max_index);
     }
 
     std::vector<Token> _multinomial_sample(const Logits& logits, size_t num_tokens_per_sequence) {