sampling: add comments on modifications

Author: kmorennv

common/sampling.cpp

@@ -187,9 +187,11 @@ std::string common_params_sampling::print() const {
 struct common_sampler * common_sampler_init(const struct llama_model * model, struct common_params_sampling & params) {
     const llama_vocab * vocab = llama_model_get_vocab(model);
 
+    // if the user did not specify a value for penalty_last_n, set it to the model's context size
     if (params.penalty_last_n == -1) {
         params.penalty_last_n = llama_model_n_ctx_train(model);
     }
+    // ensure that n_prev is at least as large as penalty_last_n,  sampler needs to remember at least that many tokens for the penalties to work correctly
     params.penalty_last_n = std::max(params.penalty_last_n, 0);
     params.n_prev = std::max(params.n_prev, params.penalty_last_n);