spec : add self speculative decoding, ngram and refactor (#1261)

* spec : add self speculative decoding and ngram-mod and refactor

common : use common_ prefix for common library function

llama : use LLAMA_TOKEN_NULL

spec : add self speculative decoding (no draft model required) + refactor

spec : add ngram-mod

spec : various improvements ton ngram-map + docs

spec : fix the check-rate logic of ngram-simple

common : add common_speculative_is_compat()

spec : simplify time measurement using common_time_meas

refactor common_sampler_init

refactor common_token_to_piece

refactor and fix cur_p bug

clean up

* spec : remove check rate

* spec: show warnings instead of abort

---------

Co-authored-by: firecoperana <firecoperana>
Co-authored-by: Sascha Rogmann <59577610+srogmann@users.noreply.github.com>

common/ngram-mod.cpp

@@ -0,0 +1,60 @@
+#include "ngram-mod.h"
+
+//
+// common_ngram_mod
+//
+
+common_ngram_mod::common_ngram_mod(uint16_t n, size_t size) : n(n), used(0) {
+    entries.resize(size);
+
+    reset();
+}
+
+size_t common_ngram_mod::idx(const entry_t * tokens) const {
+    size_t res = 0;
+
+    for (size_t i = 0; i < n; ++i) {
+        res = res*6364136223846793005ULL + tokens[i];
+    }
+
+    res = res % entries.size();
+
+    return res;
+}
+
+void common_ngram_mod::add(const entry_t * tokens) {
+    const size_t i = idx(tokens);
+
+    if (entries[i] == EMPTY) {
+        used++;
+    }
+
+    entries[i] = tokens[n];
+}
+
+common_ngram_mod::entry_t common_ngram_mod::get(const entry_t * tokens) const {
+    const size_t i = idx(tokens);
+
+    return entries[i];
+}
+
+void common_ngram_mod::reset() {
+    std::fill(entries.begin(), entries.end(), EMPTY);
+    used = 0;
+}
+
+size_t common_ngram_mod::get_n() const {
+    return n;
+}
+
+size_t common_ngram_mod::get_used() const {
+    return used;
+}
+
+size_t common_ngram_mod::size() const {
+    return entries.size();
+}
+
+size_t common_ngram_mod::size_bytes() const {
+    return entries.size() * sizeof(entries[0]);
+}