tests : try to fix tail free sampling test

ggml-ci

llama.cpp

@@ -2024,9 +2024,18 @@ void llama_sample_tail_free(struct llama_context * ctx, llama_token_data_array *
     }
 
     // Normalize the second derivatives
-    float second_derivatives_sum = std::accumulate(second_derivatives.begin(), second_derivatives.end(), 0.0f);
-    for (float & value : second_derivatives) {
-        value /= second_derivatives_sum;
+    {
+        const float second_derivatives_sum = std::accumulate(second_derivatives.begin(), second_derivatives.end(), 0.0f);
+
+        if (second_derivatives_sum > 1e-6f) {
+            for (float & value : second_derivatives) {
+                value /= second_derivatives_sum;
+            }
+        } else {
+            for (float & value : second_derivatives) {
+                value = 1.0f / second_derivatives.size();
+            }
+        }
     }
 
     float cum_sum = 0.0f;

tests/test-sampling.cpp

@@ -200,4 +200,6 @@ int main(void) {
     test_frequency_presence_penalty({0.2f, 0.2f, 0.2f, 0.2f, 0.2f}, {0, 1, 2, 0, 0}, {0.499977f, 0.499977f, 0.000023f, 0.000023f, 0.000000f}, 5.0f, 5.0f);
 
     printf("OK\n");
+
+    return 0;
 }