Fixed RNG to be reproduceable

Thanks to @slaren for directions

Author: MaggotHATE

common/sampling.cpp

@@ -185,7 +185,7 @@ struct gpt_sampler * gpt_sampler_init(const struct llama_model * model, const st
                         llama_sampler_chain_add(result->chain, llama_sampler_init_min_p    (params.min_p, params.min_keep));
                         break;
                     case GPT_SAMPLER_TYPE_XTC:
-                        llama_sampler_chain_add(result->chain, llama_sampler_init_xtc      (params.xtc_p, params.xtc_t, params.xtc_t_max, params.min_keep));
+                        llama_sampler_chain_add(result->chain, llama_sampler_init_xtc      (params.xtc_p, params.xtc_t, params.xtc_t_max, params.min_keep, params.seed));
                         break;
                     case GPT_SAMPLER_TYPE_TFS_Z:
                         llama_sampler_chain_add(result->chain, llama_sampler_init_tail_free(params.tfs_z, params.min_keep));

src/llama-sampling.cpp

@@ -1062,10 +1062,16 @@ struct llama_sampler * llama_sampler_init_temp_ext(float temp, float delta, floa
 // xtc
 
 struct llama_sampler_xtc {
-    const float  probability;
-    const float  threshold;
-    const float  threshold_max;
-    const size_t min_keep;
+    const float    probability;
+    const float    threshold;
+    const float    threshold_max;
+    const size_t   min_keep;
+
+    const uint32_t seed;
+    uint32_t       seed_cur;
+    float          chance;
+
+    std::mt19937 rng;
 };
 
 static const char * llama_sampler_xtc_name(const struct llama_sampler * /*smpl*/) {
@@ -1084,10 +1090,8 @@ static void llama_sample_xtc_apply(struct llama_sampler * smpl, llama_token_data
         || ctx->min_keep <= 2) {
         return;
     }
-
-    std::random_device rd;
-    float chance = (float)(rd()%100 - 1)/100;
-    if (chance > ctx->probability) return;
+    // chance is calculated on init and on each reset
+    if (ctx->chance > ctx->probability) return;
 
     // in case it's not sorted/recalculated yet
     llama_sampler_softmax_impl(cur_p);
@@ -1117,30 +1121,56 @@ static void llama_sample_xtc_apply(struct llama_sampler * smpl, llama_token_data
 
 static struct llama_sampler * llama_sampler_xtc_clone(const struct llama_sampler * smpl) {
     const auto * ctx = (const llama_sampler_xtc *) smpl->ctx;
-    return llama_sampler_init_xtc(ctx->probability, ctx->threshold, ctx->threshold_max, ctx->min_keep);
+    auto * result = llama_sampler_init_xtc(ctx->probability, ctx->threshold, ctx->threshold_max, ctx->min_keep, ctx->seed);
+
+    // copy the state
+    {
+        auto * result_ctx = (llama_sampler_xtc *) result->ctx;
+
+        result_ctx->rng = ctx->rng;
+    }
+
+    return result;
 }
 
 static void llama_sampler_xtc_free(struct llama_sampler * smpl) {
     delete (llama_sampler_xtc *) smpl->ctx;
 }
 
+static void llama_sampler_xtc_reset(struct llama_sampler * smpl) {
+    auto * ctx = (llama_sampler_xtc *) smpl->ctx;
+    ctx->seed_cur = get_rng_seed(ctx->seed);
+    ctx->rng.seed(ctx->seed_cur);
+
+    std::uniform_real_distribution<> distance(0.0, 1.0);
+    ctx->chance = distance(ctx->rng);
+}
+
 static struct llama_sampler_i llama_sampler_xtc_i = {
     /* .name   = */ llama_sampler_xtc_name,
     /* .accept = */ nullptr,
     /* .apply  = */ llama_sample_xtc_apply,
-    /* .reset  = */ nullptr,
+    /* .reset  = */ llama_sampler_xtc_reset,
     /* .clone  = */ llama_sampler_xtc_clone,
     /* .free   = */ llama_sampler_xtc_free,
 };
 
-struct llama_sampler * llama_sampler_init_xtc(float p, float t, float t_max, size_t min_keep) {
+struct llama_sampler * llama_sampler_init_xtc(float p, float t, float t_max, size_t min_keep, uint32_t seed) {
+    auto seed_cur = get_rng_seed(seed);
+    std::uniform_real_distribution<> distance(0.0, 1.0);
+    auto rng = std::mt19937(seed_cur);
+    float chance = distance(rng);
     return new llama_sampler {
         /* .iface = */ &llama_sampler_xtc_i,
         /* .ctx   = */ new llama_sampler_xtc {
             /* .probability   = */ p,
             /* .threshold     = */ t,
             /* .threshold_max = */ t_max,
             /* .min_keep      = */ min_keep,
+            /* .seed          = */ seed,
+            /* .seed_cur      = */ seed_cur,
+            /* .chance        = */ chance,
+            /* .rng           = */ rng,
         },
     };
 }