server : hide ctx_sampling->prev behind API (#3696)

Author: ggerganov

examples/server/server.cpp

@@ -1559,7 +1559,8 @@ struct llama_server_context
 
                     if (!slot.params.cache_prompt)
                     {
-                        std::fill(slot.ctx_sampling->prev.begin(), slot.ctx_sampling->prev.end(), 0);
+                        llama_sampling_reset(slot.ctx_sampling);
+
                         slot.n_past = 0;
                         slot.num_prompt_tokens_processed = slot.num_prompt_tokens;
                     }
@@ -1570,16 +1571,17 @@ struct llama_server_context
                             slot.params.n_keep = slot.num_prompt_tokens;
                         }
                         slot.params.n_keep = std::min(slot.n_ctx - 4, slot.params.n_keep);
-                        //if input prompt is too big, truncate like normal
+
+                        // if input prompt is too big, truncate it
                         if (slot.num_prompt_tokens >= slot.n_ctx)
                         {
-                            // applied bug of #3661
                             const int n_left = slot.n_ctx - slot.params.n_keep;
                             const int n_block_size = n_left / 2;
                             const int erased_blocks = (slot.num_prompt_tokens - slot.params.n_keep - n_block_size) / n_block_size;
+
                             std::vector<llama_token> new_tokens(prompt_tokens.begin(), prompt_tokens.begin() + slot.params.n_keep);
-                            // Use half the left-over space in the context for the prompt
                             new_tokens.insert(new_tokens.end(), prompt_tokens.begin() + slot.params.n_keep + erased_blocks * n_block_size, prompt_tokens.end());
+
                             LOG_VERBOSE("input truncated", {
                                                             {"n_ctx",  slot.n_ctx},
                                                             {"n_keep", slot.params.n_keep},
@@ -1588,14 +1590,20 @@ struct llama_server_context
                                                         });
                             slot.truncated = true;
                             prompt_tokens = new_tokens;
+
                             slot.num_prompt_tokens = prompt_tokens.size();
                             GGML_ASSERT(slot.num_prompt_tokens < slot.n_ctx);
                         }
-                        const size_t ps = slot.num_prompt_tokens;
-                        std::fill(slot.ctx_sampling->prev.begin(), slot.ctx_sampling->prev.end()  - ps, 0);
-                        std::copy(prompt_tokens.begin(), prompt_tokens.end(), slot.ctx_sampling->prev.end() - ps);
+
+                        // push the prompt into the sampling context (do not apply grammar)
+                        for (auto &token : prompt_tokens)
+                        {
+                            llama_sampling_accept(slot.ctx_sampling, ctx, token, false);
+                        }
+
                         slot.n_past = common_part(slot.cache_tokens, prompt_tokens);
                         slot.num_prompt_tokens_processed = slot.num_prompt_tokens - slot.n_past;
+
                         LOG_TEE("slot %d : in cache: %i tokens | to process: %i tokens\n", slot.id, slot.n_past, slot.num_prompt_tokens_processed);
                     }