common/ngram-map.cpp

#include "common.h"
#include "log.h"
#include "ngram-map.h"

#include <cinttypes>
#include <cstdint>
#include <cstdio>
#include <sstream>

// prime number used for LCG hash function (32 bit), it is near (sqrt(5) - 1)/2 * 2^32.
#define LCG_FACTOR 2654435761UL

// Compute the LCG hash of a n-gram of size len at offset start.
static uint32_t common_ngram_map_hash(const llama_tokens & tokens, size_t start, size_t len) {
    uint32_t hash = 0;
    for (size_t i = 0; i < len; ++i) {
        hash = hash * LCG_FACTOR + tokens[start + i];
    }
    return hash;
}

// Print the values of a sublist of `llama_tokens & inp` to a string in the form [v0, v1, v2, ...].
static std::string common_tokens_to_str(const llama_tokens & inp, size_t start, size_t length) {
    std::ostringstream oss;
    oss << '[';
    for (size_t i = 0; i < length; ++i) {
        if (i > 0) {
            oss << ", ";
        }
        oss << inp[start + i];
    }
    oss << ']';
    return oss.str();
}


// n-gram simple
//

/**
 * Perform speculative generation using the model's own token history.
 * Searches for a matching pattern in the token history and returns draft tokens.
 *
 * @param state     Current state of this implementation
 * @param tokens    Token history to search in
 * @param sampled   Last sampled token
 * @return Vector of draft tokens, empty if no matching pattern is found
 */
llama_tokens common_ngram_simple_draft(
        const common_ngram_simple_config & config,
        const llama_tokens & tokens, llama_token sampled) {

    // Simple implementation of self-speculative decoding without a draft model.
    //
    const size_t cur_len = tokens.size();

    const size_t n_draft_min = config.size_ngram; // size of n-gram to lookup in token history
    const size_t n_draft_max = config.size_mgram; // the m-gram following the found n-gram is used for draft

    // vector for tokens we want to verify.
    // return empty vector if there is no match.
    llama_tokens draft_tokens;

    // We need at least n_draft_min + n_draft_max + 1 tokens.
    if (cur_len <= static_cast<size_t>(n_draft_min + n_draft_max + 1)) {
        return draft_tokens;
    }

    // pattern search
    llama_tokens pattern;
    pattern.reserve(n_draft_min);
    for (size_t j = cur_len - n_draft_min + 1; j < cur_len; ++j) {
        pattern.push_back(tokens[j]);
    }
    pattern.push_back(sampled); // add the last token to the pattern

    size_t match_pos = 0; // we ignore position 0, position 0 == no match
                          // search backwards, but skip the current match (we are currently there)
    for (size_t j = cur_len - n_draft_min - 1; j > 0; --j) {
        bool match = true;
        for (size_t k = 0; k < pattern.size(); ++k) {
            if (tokens[j + k] != pattern[k]) {
                match = false;
                break;
            }
        }
        if (match) {
            match_pos = j;
            break;
        }
    }
    if (match_pos == 0) {
        return draft_tokens;
    }

    const size_t copy_max = std::min(
            n_draft_max,
            cur_len - (match_pos + n_draft_min)
            );
    if (copy_max < n_draft_min) {
        return draft_tokens;
    }
    LOG_DBG("%s: #tokens = %zu: found matching pattern at pos %zu, length %zu, draft length %zu\n",
            __func__, cur_len,
            match_pos, pattern.size(), copy_max);

    draft_tokens.reserve(copy_max);
    for (size_t j = 0; j < copy_max; ++j) {
        draft_tokens.push_back(tokens[match_pos + n_draft_min + j]);
    }
    return draft_tokens;
}


// n-gram map
//

// maximum number of counted values of a ngram map value.
#define COMMON_NGRAM_MAX_VALUE_COUNT 16380

void common_ngram_map_begin(
    common_ngram_map & map, const llama_tokens & tokens) {
    size_t size_begin = tokens.size();

    LOG_DBG("%s: begin, idx_last_draft=%zu, new begin=%zu, #keys=%zu\n", __func__,
            map.idx_last_check, size_begin, map.keys.size());

    size_t count_map_entries_upd = 0;
    if (!map.key_map.empty() && size_begin < map.idx_last_check) {
        if (map.show_key_map_stats) {
            // Print statistics of hash map map_key.
            size_t count_nonzero = 0;
            uint32_t min_idx = UINT32_MAX;
            uint32_t max_idx = 0;
            for (size_t i = 0; i < map.key_map.size(); ++i) {
                uint32_t key_idx = map.key_map[i];
                if (key_idx != 0) {
                    ++count_nonzero;
                    if (key_idx < min_idx) min_idx = key_idx;
                    if (key_idx > max_idx) max_idx = key_idx;
                }
            }
            if (count_nonzero == 0) {
                min_idx = 0;
            }
            LOG_INF("%s: key_map stats: entries=%zu, min_idx=%u, max_idx=%u, key_map_last_idx=%u\n",
                    __func__, count_nonzero, min_idx, max_idx, map.key_map_last_idx);
        }

        // Update the map from hash to key index (clear outdated entries).
        for (size_t i = 0; i < map.key_map.size(); ++i) {
            uint32_t key_idx = map.key_map[i];
            if (key_idx >= map.size_last_begin) {
                map.key_map[i] = 0;
                count_map_entries_upd++;
            }
        }
        map.key_map_last_idx = (map.size_last_begin > 0) ? map.size_last_begin - 1 : 0;
    }

    if (size_begin < map.idx_last_check && !map.keys.empty()) {
        // The next token generation will start at index size_begin.
        // The tokens between map.size_last_begin and size_begin are no longer valid.
        //
        // Refresh map: Remove all entries with index >= map.size_last_begin.
        size_t count_keys = map.keys.size();
        size_t count_keys_del = 0;
        size_t count_values_del = 0;
        for (int32_t i = map.keys.size() - 1; i >= 0; --i) {
            common_ngram_map_key & key = map.keys[i];
            if (key.key_idx >= map.size_last_begin) {
                // Delete the key.
                LOG_DBG("%s: delete key %d at index %zu (>= size_last_begin=%zu)\n", __func__, i, key.key_idx, map.size_last_begin);
                map.keys.erase(map.keys.begin() + i);
                count_keys_del++;
                continue;
            }
            if (map.key_only) {
                continue;
            }

            // Check the indices of the values.
            for (int16_t j = COMMON_NGRAM_MAX_VALUES - 1; j >= 0; --j) {
                common_ngram_map_value & value = key.values[j];
                if (value.value_idx >= map.size_last_begin) {
                    // Delete the value.
                    count_values_del++;

                    // Move all values after this value to the left.
                    for (uint16_t k = j; k < COMMON_NGRAM_MAX_VALUES - 1; ++k) {
                        key.values[k] = key.values[k + 1];
                    }
                    // Clear the last value.
                    key.values[COMMON_NGRAM_MAX_VALUES - 1].value_idx = 0;
                    key.values[COMMON_NGRAM_MAX_VALUES - 1].value_num = 0;
                }
            }
            if (key.values[0].value_idx == 0) {
                // No values left, delete the key.
                LOG_DBG("%s: delete key %d at index %zu (no values left)\n", __func__, i, key.key_idx);
                map.keys.erase(map.keys.begin() + i);
                count_keys_del++;
            }
        }

        LOG_INF("%s: refresh map: idx_last_draft=%zu, new begin=%zu, #keys_checked=%zu, #keys_del=%zu, #values_del=%zu, #hashes_upd=%zu\n", __func__,
                map.idx_last_check, size_begin,
                count_keys, count_keys_del, count_values_del, count_map_entries_upd);
    }

    map.idx_last_check = (map.size_last_begin > 0) ? map.size_last_begin - 1 : 0;
    map.size_last_begin = size_begin;
}

void common_ngram_map_draft(common_ngram_map & map,
        const llama_tokens & inp, llama_token sampled,
        llama_tokens & draft) {
    // reset last key and value.
    map.last_draft_created   = false;
    map.last_draft_key_idx   = 0;
    map.last_draft_value_idx = 0;

    const size_t cur_len = inp.size();
    const uint16_t n = map.size_key;
    const uint16_t m = map.size_value;
    if (cur_len < static_cast<size_t>(2 * n + m)) {
        return;
    }
    if (cur_len >= static_cast<size_t>(UINT32_MAX)) {
        // key_map uses uint32_t instead of size_t.
        GGML_ABORT("%s: cur_len exceeds UINT32_MAX: %zu", __func__, cur_len);
    }

    if (map.idx_last_check  > cur_len) {
        // Should not happen because of common_ngram_map_begin().
        GGML_ABORT("%s: map.idx_last_check > cur_len: %zu > %zu", __func__, map.idx_last_check, cur_len);
    }
    map.idx_last_check = cur_len;

    // search pattern, the key n-gram
    std::vector<llama_token> key_tokens;
    key_tokens.reserve(n);
    for (size_t j = cur_len - n + 1; j < cur_len; ++j) {
        key_tokens.push_back(inp[j]);
    }
    key_tokens.push_back(sampled);

    // search for the key in the map
    size_t match_pos = 0;
    if (map.size_last_begin > cur_len) {
        GGML_ABORT("%s: map.size_last_begin > cur_len: %zu > %zu", __func__, map.size_last_begin, cur_len);
    }
    if (!map.key_map.empty()) {
        // Search for the key in the map key_map from hash of ngrams to index of ngram.
        uint32_t idx_hash = (common_ngram_map_hash(key_tokens, 0, n) % map.key_map.size());
        uint32_t idx_key = map.key_map[idx_hash];
        if (idx_key != 0 && idx_key < cur_len - n - m - 1) {
            // Check if the key matches the key at idx_key (because of possible collisions).
            bool match = true;
            for (size_t k = 0; k < n; ++k) {
                if (inp[idx_key + k] != key_tokens[k]) {
                    match = false;
                    break;
                }
            }
            LOG_DBG("%s: key hash %x -> idx_key %d: match %d\n", __func__, idx_hash, idx_key, match ? 1 : 0);
            if (match) {
                match_pos = idx_key;
            }
        }
    }
    if (match_pos == 0 && map.size_last_begin > (size_t) (n + m + 1)) {
        // Search for the key in [1, map.size_last_begin - n - m -1], descending.
        for (size_t j = map.size_last_begin - n - m - 1; j > map.key_map_last_idx; --j) {
            // Check if the key matches the key.
            bool match = true;
            for (size_t k = 0; k < n; ++k) {
                if (inp[j + k] != key_tokens[k]) {
                    match = false;
                    break;
                }
            }
            if (match) {
               match_pos = j;
               break;
            }
        }
    }
    if (match_pos == 0) {
        // In case of a reasoning chat, the part after size_last_begin may be deleted/reordered later.
        //
        // Search in [size_last_begin, cur_len - n - m - 1], descending.
        for (size_t j = cur_len - n - m - 1; j > map.size_last_begin && j > map.key_map_last_idx; --j) {
            bool match = true;
            for (size_t k = 0; k < n; ++k) {
                if (inp[j + k] != key_tokens[k]) {
                    match = false;
                    break;
                }
            }
            if (match) {
               match_pos = j;
               break;
            }
        }
    }
    if (match_pos > 0) {
        LOG_DBG("%s: cur_len = %zu, n = %d, m = %d, sz_tkns = %zu, sampled = %d, match_pos = %zu\n", __func__,
            cur_len, n, m, key_tokens.size(), sampled, match_pos);
    }

    if (!map.key_map.empty()) {
        // Add hashes of new ngrams in key_map.
        //
        // Use the same order as above.
        if (map.size_last_begin > (size_t) (n + m + 1)) {
            for (size_t j = map.size_last_begin - n - m - 1; j > map.key_map_last_idx; --j) {
                // compute hash and store index of ngram at idx j in the map.
                uint32_t idx_hash = (common_ngram_map_hash(inp, j, n) % map.key_map.size());
                if (map.key_map[idx_hash] == 0) {
                    map.key_map[idx_hash] = j; // collisions may occur
                }
            }
        }

        for (size_t j = cur_len - n - m - 1; j > map.size_last_begin && j > map.key_map_last_idx; --j) {
            // compute hash and store index of ngram at idx j in the map.
            uint32_t idx_hash = (common_ngram_map_hash(inp, j, n) % map.key_map.size());
            if (map.key_map[idx_hash] == 0) {
                map.key_map[idx_hash] = j;
            }
        }
        map.key_map_last_idx = std::max(static_cast<uint32_t>(cur_len - n - m - 1), map.key_map_last_idx);
    }

    if (match_pos == 0) {
        return;
    }

    // We have a match, now we look for the statistics of the key.
    size_t key_offset = map.keys.size(); // offset in the map
    // We iterate through the std::vector<common_ngram_map_key> map->keys.
    for (size_t i = 0; i < map.keys.size(); ++i) {
        bool match = true;
        for (size_t j = 0; j < n; ++j) {
            if (inp[map.keys[i].key_idx + j] != key_tokens[j]) {
                match = false;
                break;
            }
        }
        if (match) {
            key_offset = i;
            break;
        }
    }
    if (key_offset == map.keys.size()) {
        // We create a new key-entry, it will get offset key_offset.
        common_ngram_map_key new_key;
        new_key.key_idx = match_pos;
        new_key.stat_idx = 0;
        new_key.key_num = 0;
        for (int i = 0; i < COMMON_NGRAM_MAX_VALUES; ++i) {
            new_key.values[i].value_num = 0;
            new_key.values[i].n_accepted = m;
        }
        map.keys.push_back(new_key);
    }

    // our key n-gram:
    common_ngram_map_key & curr_key = map.keys[key_offset];

    // update number of key hits
    curr_key.key_num = (uint16_t) std::min((int) map.keys[key_offset].key_num + 1,
            (int) COMMON_NGRAM_MAX_VALUE_COUNT);

    if (map.key_only) {
        // simple mode:
        // Fill in the draft with the m tokens following the key.
        // We work with value values[0] only.
        int n_draft_tokens = std::min((int) m, (int) curr_key.values[0].n_accepted);

        for (int i = 0; i < n_draft_tokens; ++i) {
            draft.push_back(inp[match_pos + n + i]);
        }

        LOG_DBG("%s: key_idx = %zu, key_offset = %zu, key_num = %d, draft.size = %zu\n", __func__,
                curr_key.key_idx, key_offset, curr_key.key_num, draft.size());

        map.last_draft_created   = false;
        map.last_draft_key_idx   = key_offset;
        map.last_draft_value_idx = 0; // value 0 is used for simple mode
        return;
    }

    if (curr_key.key_num < map.min_hits) {
        // not enough hits to consider this a good draft
        LOG_DBG("%s: key_offset = %zu, key_num = %d, min_hits = %d, no draft\n", __func__,
                key_offset, curr_key.key_num, map.min_hits);
        return;
    }

    // complex mode: examine the different m-grams after this key n-gram.
    //

    // determine all (max COMMON_NGRAM_MAX_VALUES) m-grams after the key n-gram.
    for (size_t i = curr_key.stat_idx; i <= match_pos; ++i) {
        // begins the key n-gram at index i?
        bool match_key = true;
        for (size_t k = 0; k < n; ++k) {
            if (inp[i + k] != key_tokens[k]) {
                match_key = false;
                break;
            }
        }
        if (!match_key) {
            continue;
        }

        // Do we haven a existing value m-gram or a new one after the key at index i?
        size_t idx_begin_value_key = i + n;
        int idx_value = -1;
        for (int v = 0; v < COMMON_NGRAM_MAX_VALUES; ++v) {
            size_t idx_begin_value_v = curr_key.values[v].value_idx;
            if (idx_begin_value_v == 0) {
                // We found an empty value slot => we found a new value m-gram after the key n-gram.
                curr_key.values[v].value_idx = idx_begin_value_key;
                curr_key.values[v].value_num = 0;
                curr_key.values[v].n_accepted = m;
                idx_value = v;
                break;
            }
            bool match = true;
            for (size_t j = 0; j < m; ++j) {
                if (inp[idx_begin_value_key + j] != inp[idx_begin_value_v + j]) {
                    match = false;
                    break;
                }
            }
            if (match) {
                // We found an existing value m-gram after the key n-gram.
                idx_value = v;
                break;
            }
        }
        if (idx_value >= 0) {
            // We found a value m-gram of the key n-gram.
            curr_key.values[idx_value].value_num = (uint16_t) std::min((int) curr_key.values[idx_value].value_num + 1,
                    (int) COMMON_NGRAM_MAX_VALUE_COUNT);
        }
    }
    // the statistics are updated up to match_pos.
    curr_key.stat_idx = match_pos;

    // Do we have a value we could use for the draft?
    uint16_t max_occur = 0;
    int slot_max = 0;
    for (int v = 0; v < COMMON_NGRAM_MAX_VALUES; ++v) {
        uint16_t curr_occur = curr_key.values[v].value_num;
        if (curr_occur > max_occur) {
            max_occur = curr_occur;
            slot_max = v;
        }
    }
    // What is sum of the other occurrences?
    uint32_t sum_occur = 0;
    for (int v = 0; v < COMMON_NGRAM_MAX_VALUES; ++v) {
        if (v == slot_max) {
            continue;
        }
        uint16_t curr_occur = curr_key.values[v].value_num;
        sum_occur += curr_occur;
    }

    LOG_INF("%s: key_offset = %zu, max_occur = %d, sum_occur = %d, slot_max = %d [%zu/%d, %zu/%d, %zu/%d, %zu/%d]\n", __func__,
            key_offset,
            max_occur, sum_occur, slot_max,
            curr_key.values[0].value_idx, curr_key.values[0].value_num,
            curr_key.values[1].value_idx, curr_key.values[1].value_num,
            curr_key.values[2].value_idx, curr_key.values[2].value_num,
            curr_key.values[3].value_idx, curr_key.values[3].value_num
        );
    // Print the tokens of the four values (if idx != 0), use LOG_INF
    for (int v = 0; v < COMMON_NGRAM_MAX_VALUES; ++v) {
        if (curr_key.values[v].value_idx != 0) {
            LOG_INF("%s: value[%d] = %s\n", __func__, v, common_tokens_to_str(inp, curr_key.values[v].value_idx, m).c_str());
        }
    }

    if (sum_occur > 0 && max_occur < 2 * sum_occur) {
        // The most frequent value is not much more frequent than the other values.
        // We do not use the draft.
        return;
    }

    // We use the most frequent value values[slot_max] for the draft.
    // Fill in the draft with the m tokens following the key.
    int n_draft_tokens = std::min((int) m, (int) curr_key.values[slot_max].n_accepted);

    for (int i = 0; i < n_draft_tokens; ++i) {
        draft.push_back(inp[match_pos + n + i]);
    }

    LOG_INF("%s: key_offset = %zu, slot_max = %d, key_num = %d, draft.size = %zu\n", __func__,
            key_offset, slot_max,
            curr_key.key_num, draft.size());

    map.last_draft_created   = true;
    map.last_draft_key_idx   = key_offset;
    map.last_draft_value_idx = slot_max; // value used for draft generation.
}

void common_ngram_map_accept(common_ngram_map & map, uint16_t n_accepted) {
    if (!map.last_draft_created) {
        return;
    }

    // find the key and its chosen value.
    const size_t key_idx = map.last_draft_key_idx;
    const size_t val_idx = map.last_draft_value_idx;

    // find key corresponding to key_idx.
    common_ngram_map_key & curr_key = map.keys[key_idx];
    // find value corresponding to val_idx.
    struct common_ngram_map_value & curr_value = curr_key.values[val_idx]; // value used for draft generation.

    // update the value statistics
    LOG_INF("common_ngram_map_send_accepted: n_accepted = %d, prev value_num = %d\n",
            n_accepted, curr_value.n_accepted);
    curr_value.n_accepted = n_accepted;
}