Shift all values by the max value before applying logsoftmax

Author: bullno1

llama.cpp

@@ -2143,10 +2143,18 @@ void llama_sample_frequency_and_presence_penalties(struct llama_context * ctx, l
 
 template<typename T, typename LogitAccessor>
 void llama_log_softmax(T * array, int size, LogitAccessor logit_accessor) {
+    T* element = std::max_element(
+        array, array + size,
+        [&logit_accessor](T& lhs, T& rhs) {
+            return logit_accessor(lhs) < logit_accessor(rhs);
+        }
+    );
+
+    float max_l = logit_accessor(*element);
     float sum = 0.f;
     for (int i = 0; i < size; ++i) {
         float& logit = logit_accessor(array[i]);
-        float p = expf(logit);
+        float p = expf(logit - max_l);
         sum += p;
         logit = p;
     }