speculative : add tree-based sampling example (#3624)

* sampling : one sequence per sampling context

ggml-ci

* speculative : add tree-based sampling support

ggml-ci

* speculative : reuse the n_parallel CLI param

* speculative : refactor sampling

* examples : fix build after sampling refactoring

ggml-ci

* batched : fix n_seq_id

* sampling : fix malloc

ggml-ci

* swift : fix build

ggml-ci

* swift : try to fix build

ggml-ci

* prompts : add assistant.txt

* common : add llama_batch_add() and llama_batch_clear() helpers

* speculative : minor refactor

ggml-ci

* minor : comments + rename

ggml-ci

* speculative : fix off-by-one for n_drafted

* speculative : fix the n_drafted fix + p constants

common/sampling.h

@@ -2,6 +2,8 @@
 
 #include "llama.h"
 
+#include "grammar-parser.h"
+
 #include <string>
 #include <vector>
 #include <unordered_map>
@@ -34,75 +36,64 @@ typedef struct llama_sampling_params {
 
 } llama_sampling_params;
 
-// per-sequence sampler context
-typedef struct llama_sampler_sequence_context {
-    float mirostat_mu; // mirostat sampler state
-    llama_grammar * grammar;
-} llama_sampler_sequence_context;
-
 // general sampler context
-typedef struct llama_sampling_context {
-    ~llama_sampling_context();
-
-    // parameters that will be used for sampling and when creating
-    // new llama_sampler_sequence_context instances
+// TODO: move to llama.h
+struct llama_sampling_context {
+    // parameters that will be used for sampling
     llama_sampling_params params;
 
-    // map of sequence ids to sampler contexts
-    std::unordered_map<llama_seq_id, llama_sampler_sequence_context> sequence_contexts;
+    // mirostat sampler state
+    float mirostat_mu;
 
-    // when non-NULL, new instances of llama_sampler_sequence_context
-    // will get a copy of the grammar here
-    // note: only the pointer is stored here, it is not a copy of
-    //       the grammar and shouldn't be freed
     llama_grammar * grammar;
-} llama_sampling_context;
+
+    // internal
+    grammar_parser::parse_state parsed_grammar;
+
+    // TODO: replace with ring-buffer
+    std::vector<llama_token>      prev;
+    std::vector<llama_token_data> cur;
+};
 
 #include "common.h"
 
 // Create a new sampling context instance.
-llama_sampling_context llama_sampling_context_init(
-        const struct gpt_params & params,
-                  llama_grammar * grammar = NULL);
+struct llama_sampling_context * llama_sampling_init(const struct gpt_params & params);
 
-// Fetches the sampler context for the specified sequence id (defaults to 0).
-// If the context for that sequence id doesn't already exist, it will be created with
-// default values based on the parameters in the ctx_sampling argument.
-llama_sampler_sequence_context & llama_sampling_get_sequence_context(
-              llama_sampling_context & ctx_sampling,
-        const llama_seq_id             seq = 0);
+void llama_sampling_free(struct llama_sampling_context * ctx);
 
-// Reset the sampler context for the supplied sequence id (defaults to 0).
-// This is necessary to reuse a sequence id or free memory used by sequences
-// that are no longer required.
-bool llama_sampling_context_reset(
-              llama_sampling_context & ctx_sampling,
-        const llama_seq_id             seq = 0);
+// Reset the sampler context
+// - clear prev tokens
+// - reset grammar
+void llama_sampling_reset(llama_sampling_context * ctx);
+
+// Copy the sampler context
+void llama_sampling_cp(llama_sampling_context * src, llama_sampling_context * dst);
 
 // this is a common sampling function used across the examples for convenience
 // it can serve as a starting point for implementing your own sampling function
 // Note: When using multiple sequences, it is the caller's responsibility to call
-//       llama_sampling_context_reset when a sequence ends
+//       llama_sampling_reset when a sequence ends
 //
 // required:
-//  - ctx:          context to use for sampling
+//  - ctx_main:     context to use for sampling
 //  - ctx_sampling: sampling-specific context
 //
 // optional:
-//  - ctx_guidance:  context to use for classifier-free guidance, ignore if NULL
-//  - last_tokens:   needed for repetition penalty, ignore if empty
-//  - idx:           sample from llama_get_logits_ith(ctx, idx)
-//  - seq:           sequence id to associate sampler state with
+//  - ctx_cfg:      context to use for classifier-free guidance
+//  - idx:          sample from llama_get_logits_ith(ctx, idx)
 //
 // returns:
 //  - token:      sampled token
 //  - candidates: vector of candidate tokens
 //
 llama_token llama_sampling_sample(
-                  struct llama_context * ctx,
-                  struct llama_context * ctx_guidance,
-                  struct llama_sampling_context & ctx_sampling,
-        const std::vector<llama_token> & last_tokens,
-         std::vector<llama_token_data> & candidates,
-        const                      int   idx = 0,
-                          llama_seq_id   seq = 0);
+        struct llama_sampling_context * ctx_sampling,
+        struct llama_context * ctx_main,
+        struct llama_context * ctx_cfg,
+        int idx = 0);
+
+void llama_sampling_accept(
+        struct llama_sampling_context * ctx_sampling,
+        struct llama_context * ctx_main,
+        llama_token id);