llama : default sampling changes + greedy update (#9897)

* llama : deprecate softmax sampler + fix dist sampler

ggml-ci

* tests : replace macros with functions

ggml-ci

* sampling : change temperature sampler logic

For t <= 0.0f, keep the max logit intact and set the rest to -inf

* cont : no need for special "greedy" logic

top-k == 1 is the same

* tests : init prob correctly

* llama : handle temp <= 0.0 in the temp_ext sampler too

ggml-ci

* cont : avoid extra loop in temperature sampler for sub-zero temp

ggml-ci

src/llama-sampling.cpp

@@ -63,6 +63,30 @@ static void llama_log_softmax(float * array, size_t size) {
 }
 */
 
+static void llama_sampler_temp_impl(llama_token_data_array * cur_p, float temp) {
+    if (temp <= 0.0f) {
+        // find the token with the highest logit and set the rest to -inf
+        size_t max_i = 0;
+        float  max_l = cur_p->data[0].logit;
+
+        for (size_t i = 1; i < cur_p->size; ++i) {
+            if (cur_p->data[i    ].logit > max_l) {
+                cur_p->data[max_i].logit = -INFINITY;
+                max_i = i;
+                max_l = cur_p->data[i].logit;
+            } else {
+                cur_p->data[i].logit = -INFINITY;
+            }
+        }
+
+        return;
+    }
+
+    for (size_t i = 0; i < cur_p->size; ++i) {
+        cur_p->data[i].logit /= temp;
+    }
+}
+
 static void llama_sampler_softmax_impl(llama_token_data_array * cur_p) {
     GGML_ASSERT(cur_p->size > 0);
 
@@ -427,6 +451,9 @@ static const char * llama_sampler_dist_name(const struct llama_sampler * /*smpl*
 
 static void llama_sampler_dist_apply(struct llama_sampler * smpl, llama_token_data_array * cur_p) {
     auto * ctx = (llama_sampler_dist *) smpl->ctx;
+
+    llama_sampler_softmax_impl(cur_p);
+
     cur_p->selected = llama_sample_dist(cur_p, ctx->rng);
 }
 
@@ -912,9 +939,8 @@ static const char * llama_sampler_temp_name(const struct llama_sampler * /*smpl*
 
 static void llama_sampler_temp_apply(struct llama_sampler * smpl, llama_token_data_array * cur_p) {
     const auto * ctx = (llama_sampler_temp *) smpl->ctx;
-    for (size_t i = 0; i < cur_p->size; ++i) {
-        cur_p->data[i].logit /= ctx->temp;
-    }
+
+    llama_sampler_temp_impl(cur_p, ctx->temp);
 }
 
 static struct llama_sampler * llama_sampler_temp_clone(const struct llama_sampler * smpl) {
@@ -961,6 +987,7 @@ static void llama_sampler_temp_ext_apply(struct llama_sampler * smpl, llama_toke
     if (ctx->delta > 0) {
         const float min_temp = std::max(0.0f, ctx->temp - ctx->delta);
         const float max_temp = ctx->temp + ctx->delta;
+
         float exponent_val = ctx->exponent;
 
         // no need to do anything if there is only one (or zero) candidates
@@ -998,9 +1025,7 @@ static void llama_sampler_temp_ext_apply(struct llama_sampler * smpl, llama_toke
     #endif
 
         // Apply the dynamically calculated temperature scaling
-        for (size_t i = 0; i < cur_p->size; ++i) {
-            cur_p->data[i].logit /= dyn_temp;
-        }
+        llama_sampler_temp_impl(cur_p, dyn_temp);
 
         // Re-compute softmax probabilities after scaling logits with dynamic temperature
         const double max_l_double = cur_p->data[0].logit;
@@ -1024,9 +1049,7 @@ static void llama_sampler_temp_ext_apply(struct llama_sampler * smpl, llama_toke
         }
     #endif
     } else {
-        for (size_t i = 0; i < cur_p->size; ++i) {
-            cur_p->data[i].logit /= ctx->temp;
-        }
+        llama_sampler_temp_impl(cur_p, ctx->temp);
     }
 }