Reasoning budget updates

common/CMakeLists.txt

@@ -81,6 +81,8 @@ add_library(${TARGET} STATIC
     preset.cpp
     preset.h
     regex-partial.cpp
+    reasoning-budget.cpp
+    reasoning-budget.h
     regex-partial.h
     sampling.cpp
     sampling.h

common/reasoning-budget.cpp

@@ -0,0 +1,219 @@
+#include "reasoning-budget.h"
+#include "common.h"
+#include "unicode.h"
+
+#include "log.h"
+
+#include <cmath>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+struct token_matcher {
+    std::vector<llama_token> tokens;
+    size_t pos = 0;
+
+    bool advance(llama_token token) {
+        if (tokens.empty()) {
+            return false;
+        }
+
+        if (token == tokens[pos]) {
+            pos++;
+            if (pos >= tokens.size()) {
+                pos = 0;
+                return true;
+            }
+        } else {
+            pos = 0;
+            if (token == tokens[0]) {
+                pos = 1;
+            }
+        }
+        return false;
+    }
+
+    void reset() { pos = 0; }
+};
+
+struct common_reasoning_budget_ctx {
+    const llama_vocab * vocab;
+
+    token_matcher start_matcher;
+    token_matcher end_matcher;
+    std::vector<llama_token> forced_tokens;
+
+    int32_t budget;           // maximum tokens in reasoning block
+    int32_t remaining;        // tokens remaining in budget
+
+    common_reasoning_budget_state state;
+
+    // for forcing
+    size_t force_pos;         // next position in forced_tokens to force
+};
+
+static const char * common_reasoning_budget_name(const struct llama_sampler * /*smpl*/) {
+    return "reasoning-budget";
+}
+
+static void common_reasoning_budget_accept(struct llama_sampler * smpl, llama_token token) {
+    auto * ctx = (common_reasoning_budget_ctx *) smpl->ctx;
+
+    switch (ctx->state) {
+        case REASONING_BUDGET_IDLE:
+        {
+            if (ctx->start_matcher.advance(token)) {
+                ctx->state = REASONING_BUDGET_COUNTING;
+                ctx->remaining = ctx->budget;
+                LOG_INF("reasoning-budget: activated, budget=%d tokens\n", ctx->budget);
+
+                if (ctx->remaining <= 0) {
+                    ctx->state = REASONING_BUDGET_FORCING;
+                    ctx->force_pos = 0;
+                    LOG_INF("reasoning-budget: budget=0, forcing immediately\n");
+                }
+            }
+            break;
+        }
+        case REASONING_BUDGET_COUNTING:
+        case REASONING_BUDGET_WAITING_UTF8:
+        {
+            if (ctx->end_matcher.advance(token)) {
+                ctx->state = REASONING_BUDGET_DONE;
+                LOG_INF("reasoning-budget: deactivated (natural end)\n");
+                break;
+            }
+
+            bool utf8_complete = true;
+            if (ctx->vocab != nullptr) {
+                const std::string piece = common_token_to_piece(ctx->vocab, token, false);
+                utf8_complete = common_utf8_is_complete(piece);
+            }
+
+            if (ctx->state == REASONING_BUDGET_WAITING_UTF8) {
+                if (utf8_complete) {
+                    ctx->state = REASONING_BUDGET_FORCING;
+                    ctx->force_pos = 0;
+                    ctx->end_matcher.reset();
+                    LOG_INF("reasoning-budget: UTF-8 complete, now forcing end sequence\n");
+                }
+            } else if (ctx->state == REASONING_BUDGET_COUNTING) {
+                ctx->remaining--;
+                if (ctx->remaining <= 0) {
+                    if (utf8_complete) {
+                        ctx->state = REASONING_BUDGET_FORCING;
+                        ctx->force_pos = 0;
+                        ctx->end_matcher.reset();
+                        LOG_INF("reasoning-budget: budget exhausted, forcing end sequence\n");
+                    } else {
+                        ctx->state = REASONING_BUDGET_WAITING_UTF8;
+                        ctx->end_matcher.reset();
+                        LOG_INF("reasoning-budget: budget exhausted, waiting for UTF-8 completion\n");
+                    }
+                }
+            }
+            break;
+        }
+        case REASONING_BUDGET_FORCING:
+            // force_pos is advanced in apply(), not here.
+            // This ensures the first forced token isn't skipped when the sampler
+            // is initialized directly in FORCING state (e.g. COUNTING + budget=0)
+            break;
+        case REASONING_BUDGET_DONE:
+            break;
+    }
+}
+
+static void common_reasoning_budget_apply(struct llama_sampler * smpl, llama_token_data_array * cur_p) {
+    auto * ctx = (common_reasoning_budget_ctx *) smpl->ctx;
+
+    if (ctx->state != REASONING_BUDGET_FORCING) {
+        // passthrough — don't modify logits
+        return;
+    }
+
+    if (ctx->force_pos >= ctx->forced_tokens.size()) {
+        return;
+    }
+
+    const llama_token forced = ctx->forced_tokens[ctx->force_pos];
+
+    // set all logits to -inf except the forced token
+    for (size_t i = 0; i < cur_p->size; i++) {
+        if (cur_p->data[i].id != forced) {
+            cur_p->data[i].logit = -INFINITY;
+        }
+    }
+
+    // advance to next forced token (done here rather than in accept so that
+    // the first forced token isn't skipped when starting in FORCING state)
+    ctx->force_pos++;
+    if (ctx->force_pos >= ctx->forced_tokens.size()) {
+        ctx->state = REASONING_BUDGET_DONE;
+        LOG_INF("reasoning-budget: forced sequence complete, done\n");
+    }
+}
+
+static void common_reasoning_budget_reset(struct llama_sampler * smpl) {
+    auto * ctx = (common_reasoning_budget_ctx *) smpl->ctx;
+    ctx->state = REASONING_BUDGET_IDLE;
+    ctx->remaining = ctx->budget;
+    ctx->start_matcher.reset();
+    ctx->end_matcher.reset();
+    ctx->force_pos = 0;
+}
+
+static struct llama_sampler * common_reasoning_budget_clone(const struct llama_sampler * smpl) {
+    const auto * ctx = (const common_reasoning_budget_ctx *) smpl->ctx;
+    return common_reasoning_budget_init(
+        ctx->vocab,
+        ctx->start_matcher.tokens,
+        ctx->end_matcher.tokens,
+        ctx->forced_tokens,
+        ctx->budget,
+        ctx->state);
+}
+
+static void common_reasoning_budget_free(struct llama_sampler * smpl) {
+    delete (common_reasoning_budget_ctx *) smpl->ctx;
+}
+
+static struct llama_sampler_i common_reasoning_budget_i = {
+    /* .name              = */ common_reasoning_budget_name,
+    /* .accept            = */ common_reasoning_budget_accept,
+    /* .apply             = */ common_reasoning_budget_apply,
+    /* .reset             = */ common_reasoning_budget_reset,
+    /* .clone             = */ common_reasoning_budget_clone,
+    /* .free              = */ common_reasoning_budget_free,
+    /* .backend_init      = */ nullptr,
+    /* .backend_accept    = */ nullptr,
+    /* .backend_apply     = */ nullptr,
+    /* .backend_set_input = */ nullptr,
+};
+
+struct llama_sampler * common_reasoning_budget_init(
+        const struct llama_vocab       * vocab,
+        const std::vector<llama_token> & start_tokens,
+        const std::vector<llama_token> & end_tokens,
+        const std::vector<llama_token> & forced_tokens,
+        int32_t                          budget,
+        common_reasoning_budget_state    initial_state) {
+    // promote COUNTING with budget <= 0 to FORCING
+    if (initial_state == REASONING_BUDGET_COUNTING && budget <= 0) {
+        initial_state = REASONING_BUDGET_FORCING;
+    }
+
+    return llama_sampler_init(
+        /* .iface = */ &common_reasoning_budget_i,
+        /* .ctx   = */ new common_reasoning_budget_ctx {
+            /* .vocab         = */ vocab,
+            /* .start_matcher = */ { start_tokens, 0 },
+            /* .end_matcher   = */ { end_tokens, 0 },
+            /* .forced_tokens = */ forced_tokens,
+            /* .budget        = */ budget,
+            /* .remaining     = */ budget,
+            /* .state         = */ initial_state,
+            /* .force_pos     = */ 0,
+        }
+    );
+}

common/reasoning-budget.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "llama.h"
+
+#include <cstdint>
+#include <vector>
+
+enum common_reasoning_budget_state {
+    REASONING_BUDGET_IDLE,         // waiting for start sequence
+    REASONING_BUDGET_COUNTING,     // counting down tokens
+    REASONING_BUDGET_FORCING,      // forcing budget message + end sequence
+    REASONING_BUDGET_WAITING_UTF8, // budget exhausted, waiting for UTF-8 completion
+    REASONING_BUDGET_DONE,         // passthrough forever
+};
+
+// Creates a reasoning budget sampler that limits token generation inside a
+// reasoning block (e.g. between <think> and </think>).
+//
+// State machine: IDLE -> COUNTING -> WAITING_UTF8 -> FORCING -> DONE
+//   IDLE:         passthrough, watching for start_tokens sequence
+//   COUNTING:     counting down remaining tokens, watching for natural end_tokens
+//   WAITING_UTF8: budget exhausted, allowing tokens to complete a UTF-8 sequence
+//   FORCING:      forces forced_tokens token-by-token (all other logits -> -inf)
+//   DONE:         passthrough forever
+//
+// Parameters:
+//   vocab         - vocabulary (used for UTF-8 boundary detection; can be nullptr)
+//   start_tokens  - token sequence that activates counting
+//   end_tokens    - token sequence for natural deactivation
+//   forced_tokens - token sequence forced when budget expires
+//   budget        - max tokens allowed in the reasoning block
+//   initial_state - initial state of the sampler (e.g. IDLE or COUNTING)
+//                   note: COUNTING with budget <= 0 is promoted to FORCING
+//
+struct llama_sampler * common_reasoning_budget_init(
+        const struct llama_vocab       * vocab,
+        const std::vector<llama_token> & start_tokens,
+        const std::vector<llama_token> & end_tokens,
+        const std::vector<llama_token> & forced_tokens,
+        int32_t                          budget,
+        common_reasoning_budget_state    initial_state);

common/sampling.cpp

@@ -2,6 +2,7 @@
 
 #include "common.h"
 #include "log.h"
+#include "reasoning-budget.h"
 
 #include <algorithm>
 #include <cmath>
@@ -252,13 +253,13 @@ struct common_sampler * common_sampler_init(const struct llama_model * model, st
 
     // reasoning budget sampler — added first so it can force tokens before other samplers
     if (params.reasoning_budget_tokens >= 0 && !params.reasoning_budget_forced.empty()) {
-        samplers.push_back(llama_sampler_init_reasoning_budget(
+        samplers.push_back(common_reasoning_budget_init(
             vocab,
-            params.reasoning_budget_start.data(),  params.reasoning_budget_start.size(),
-            params.reasoning_budget_end.data(),    params.reasoning_budget_end.size(),
-            params.reasoning_budget_forced.data(), params.reasoning_budget_forced.size(),
+            params.reasoning_budget_start,
+            params.reasoning_budget_end,
+            params.reasoning_budget_forced,
             params.reasoning_budget_tokens,
-            params.reasoning_budget_activate_immediately));
+            params.reasoning_budget_activate_immediately ? REASONING_BUDGET_COUNTING : REASONING_BUDGET_IDLE));
     }
 
     if (params.has_logit_bias()) {

common/unicode.cpp

@@ -1,8 +1,10 @@
 #include "unicode.h"
+
+#include <algorithm>
 #include <cassert>
 #include <stdexcept>
-#include <vector>
 #include <string>
+#include <vector>
 
 // implementation adopted from src/unicode.cpp
 
@@ -67,6 +69,20 @@ utf8_parse_result common_parse_utf8_codepoint(std::string_view input, size_t off
     return utf8_parse_result(utf8_parse_result::INVALID);
 }
 
+bool common_utf8_is_complete(const std::string & s) {
+    if (s.empty()) {
+        return true;
+    }
+    for (int i = 1; i <= std::min(4, (int)s.size()); i++) {
+        unsigned char c = s[s.size() - i];
+        if ((c & 0xC0) != 0x80) {
+            int expected = (c >= 0xF0) ? 4 : (c >= 0xE0) ? 3 : (c >= 0xC0) ? 2 : 1;
+            return i >= expected;
+        }
+    }
+    return false;
+}
+
 std::string common_unicode_cpts_to_utf8(const std::vector<uint32_t> & cps) {
     std::string result;
     for (size_t i = 0; i < cps.size(); ++i) {

common/unicode.h

@@ -20,6 +20,9 @@ struct utf8_parse_result {
 // Returns 0 for invalid first bytes
 size_t common_utf8_sequence_length(unsigned char first_byte);
 
+// Check if a string ends with a complete UTF-8 sequence.
+bool common_utf8_is_complete(const std::string & s);
+
 // Parse a single UTF-8 codepoint from input
 utf8_parse_result common_parse_utf8_codepoint(std::string_view input, size_t offset);
 

include/llama.h

@@ -1455,36 +1455,6 @@ extern "C" {
     //
     LLAMA_API struct llama_sampler * llama_sampler_init_infill(const struct llama_vocab * vocab);
 
-    /// @details Reasoning budget sampler. Limits the number of tokens a model can generate inside
-    ///          a reasoning block (e.g. between <think> and </think>).
-    ///
-    /// State machine: IDLE -> COUNTING -> FORCING -> DONE
-    ///   - IDLE:     passthrough, watching accepted tokens for the start sequence
-    ///   - COUNTING: counts down tokens, watching for natural end (defuse)
-    ///   - FORCING:  forces the budget message + end sequence token-by-token
-    ///   - DONE:     passthrough forever
-    ///
-    /// @param vocab              The vocabulary (for tokenization and EOG checks)
-    /// @param start_tokens       Token sequence that activates the countdown (e.g. "<think>")
-    /// @param n_start            Number of tokens in start_tokens
-    /// @param end_tokens         Token sequence that deactivates naturally (e.g. "</think>")
-    /// @param n_end              Number of tokens in end_tokens
-    /// @param forced_tokens      Token sequence forced when budget expires (e.g. "(budget exceeded)</think>")
-    /// @param n_forced           Number of tokens in forced_tokens
-    /// @param budget             Maximum number of tokens allowed in the reasoning block
-    /// @param activate_immediately    If true, skip IDLE and start in COUNTING directly
-    ///
-    LLAMA_API struct llama_sampler * llama_sampler_init_reasoning_budget(
-            const struct llama_vocab * vocab,
-                   const llama_token * start_tokens,
-                              size_t   n_start,
-                   const llama_token * end_tokens,
-                              size_t   n_end,
-                   const llama_token * forced_tokens,
-                              size_t   n_forced,
-                             int32_t   budget,
-                                bool   activate_immediately);
-
     // Returns the seed used by the sampler if applicable, LLAMA_DEFAULT_SEED otherwise
     LLAMA_API uint32_t llama_sampler_get_seed(const struct llama_sampler * smpl);