perplexity : fix even more integer overflows (ggml-org#23623)

Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>

Author: fairydreaming

tools/perplexity/perplexity.cpp

@@ -157,7 +157,7 @@ static void process_logits(std::ostream& out, int n_vocab, const float * logits,
                 break;
             }
             lock.unlock();
-            const double v = log_softmax(n_vocab, logits + size_t(i)*n_vocab, log_probs.data() + i*nv, tokens[i+1]);
+            const double v = log_softmax(n_vocab, logits + size_t(i)*n_vocab, log_probs.data() + size_t(i)*nv, tokens[i+1]);
             local_nll += v;
             local_nll2 += v*v;
         }
@@ -169,7 +169,7 @@ static void process_logits(std::ostream& out, int n_vocab, const float * logits,
     for (auto & w : workers) {
         w.join();
     }
-    out.write((const char *)log_probs.data(), n_token*nv*sizeof(uint16_t));
+    out.write((const char *)log_probs.data(), size_t(n_token)*nv*sizeof(uint16_t));
 }
 
 struct kl_divergence_result {
@@ -279,7 +279,7 @@ static void process_logits(int n_vocab, const float * logits, const int * tokens
                 break;
             }
             lock.unlock();
-            std::pair<double, float> v = log_softmax(n_vocab, logits + size_t(i)*n_vocab, base_log_probs.data() + i*nv, tokens[i+1], local_kld);
+            std::pair<double, float> v = log_softmax(n_vocab, logits + size_t(i)*n_vocab, base_log_probs.data() + size_t(i)*nv, tokens[i+1], local_kld);
             kld_values[i]    = (float)v.first;
             p_diff_values[i] = v.second;
         }