perplexity.cpp

#include "common.h"
#include "llama.h"

#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <sstream>
#include <thread>
#include <mutex>
#include <atomic>
#include <vector>
#include <array>
#include <fstream>
#include <sstream>

#if defined(_MSC_VER)
#pragma warning(disable: 4244 4267) // possible loss of data
#endif

struct results_perplexity {
    std::vector<llama_token> tokens;
    double                   ppl_value;
    std::vector<float>       logits;
    std::vector<float>       probs;
};

struct results_log_softmax {
    double log_softmax;
    float  logit;
    float  prob;
};

static void write_logfile(
    const llama_context * ctx, const gpt_params & params, const llama_model * model,
    const struct results_perplexity & results
) {
    if (params.logdir.empty()) {
        return;
    }

    if (params.hellaswag) {
        fprintf(stderr, "%s: warning: logging results is not implemented for HellaSwag. No files will be written.\n", __func__);
        return;
    }

    const std::string timestamp = get_sortable_timestamp();

    const bool success = create_directory_with_parents(params.logdir);
    if (!success) {
        fprintf(stderr, "%s: warning: failed to create logdir %s, cannot write logfile\n",
                __func__, params.logdir.c_str());
        return;
    }

    const std::string logfile_path = params.logdir + timestamp + ".yml";
    FILE * logfile = fopen(logfile_path.c_str(), "w");

    if (logfile == NULL) {
        fprintf(stderr, "%s: failed to open logfile %s\n", __func__, logfile_path.c_str());
        return;
    }

    fprintf(logfile, "binary: main\n");
    char model_desc[128];
    llama_model_desc(model, model_desc, sizeof(model_desc));
    dump_non_result_info_yaml(logfile, params, ctx, timestamp, results.tokens, model_desc);

    fprintf(logfile, "\n");
    fprintf(logfile, "######################\n");
    fprintf(logfile, "# Perplexity Results #\n");
    fprintf(logfile, "######################\n");
    fprintf(logfile, "\n");

    dump_vector_float_yaml(logfile, "logits", results.logits);
    fprintf(logfile, "ppl_value: %f\n", results.ppl_value);
    dump_vector_float_yaml(logfile, "probs", results.probs);

    llama_dump_timing_info_yaml(logfile, ctx);
    fclose(logfile);
}

static std::vector<float> softmax(const std::vector<float>& logits) {
    std::vector<float> probs(logits.size());
    float max_logit = logits[0];
    for (float v : logits) {
        max_logit = std::max(max_logit, v);
    }
    double sum_exp = 0.0;
    for (size_t i = 0; i < logits.size(); i++) {
        // Subtract the maximum logit value from the current logit value for numerical stability
        const float logit = logits[i] - max_logit;
        const float exp_logit = expf(logit);
        sum_exp += exp_logit;
        probs[i] = exp_logit;
    }
    for (size_t i = 0; i < probs.size(); i++) {
        probs[i] /= sum_exp;
    }
    return probs;
}

static results_log_softmax log_softmax(int n_vocab, const float * logits, int tok) {
    float max_logit = logits[0];
    for (int i = 1; i < n_vocab; ++i) {
        max_logit = std::max(max_logit, logits[i]);
    }
    double sum_exp = 0.0;
    for (int i = 0; i < n_vocab; ++i) {
        sum_exp += expf(logits[i] - max_logit);
    }
    return {logits[tok] - max_logit - log(sum_exp), logits[tok], expf(logits[tok] - max_logit) / (float) sum_exp};
}

static inline int nearest_int(float fval) {
    //assert(fval <= 4194303.f);
    float val = fval + 12582912.f;
    int i; memcpy(&i, &val, sizeof(int));
    return (i & 0x007fffff) - 0x00400000;
}

static double log_softmax(int n_vocab, const float * logits, uint16_t * log_prob, int tok) {
    float max_logit = logits[0];
    float min_logit = logits[0];
    for (int i = 1; i < n_vocab; ++i) {
        max_logit = std::max(max_logit, logits[i]);
        min_logit = std::min(min_logit, logits[i]);
    }
    min_logit = std::max(min_logit, max_logit - 16);
    double sum_exp = 0.0;
    for (int i = 0; i < n_vocab; ++i) {
        sum_exp += expf(logits[i] - max_logit);
    }
    const float log_sum_exp = log(sum_exp);
    const float min_log_prob = min_logit - max_logit - log_sum_exp;
    const float scale = (max_logit - min_logit)/65535.f;
    float * d = (float *)log_prob;
    d[0] = scale;
    d[1] = min_log_prob;
    log_prob += 4;
    if (scale) {
        const float inv_scale = 1/scale;
        for (int i = 0; i < n_vocab; ++i) {
            log_prob[i] = logits[i] > min_logit ? nearest_int(inv_scale*(logits[i] - min_logit)) : 0;
        }
    } else {
        std::memset(log_prob, 0, n_vocab*sizeof(uint16_t));
    }
    return max_logit + log_sum_exp - logits[tok];
}

static void process_logits(
    int n_vocab, const float * logits, const int * tokens, int n_token, std::vector<std::thread> & workers,
    double & nll, double & nll2, float * logit_history, float * prob_history
) {
    std::mutex mutex;
    int counter = 0;
    auto compute = [&mutex, &counter, &nll, &nll2, logit_history, prob_history, n_vocab, logits, tokens, n_token] () {
        double local_nll  = 0;
        double local_nll2 = 0;
        while (true) {
            std::unique_lock<std::mutex> lock(mutex);
            int i = counter++;
            if (i >= n_token) {
                nll += local_nll; nll2 += local_nll2;
                break;
            }
            lock.unlock();
            const results_log_softmax results = log_softmax(n_vocab, logits + i*n_vocab, tokens[i+1]);
            const double v = -results.log_softmax;
            local_nll += v;
            local_nll2 += v*v;

            logit_history[i] = results.logit;
            prob_history[i]  = results.prob;
        }
    };
    for (auto & w : workers) {
        w = std::thread(compute);
    }
    compute();
    for (auto & w : workers) {
        w.join();
    }
}

static void process_logits(std::ostream& out, int n_vocab, const float * logits, const int * tokens, int n_token,
        std::vector<std::thread> & workers, std::vector<uint16_t> & log_probs, double & nll, double & nll2) {
    std::mutex mutex;
    const int nv = 2*((n_vocab + 1)/2) + 4;
    int counter = 0;
    auto compute = [&mutex, &counter, &log_probs, &nll, &nll2, n_vocab, logits, tokens, n_token, nv] () {
        double local_nll  = 0;
        double local_nll2 = 0;
        while (true) {
            std::unique_lock<std::mutex> lock(mutex);
            int i = counter++;
            if (i >= n_token) {
                nll += local_nll; nll2 += local_nll2;
                break;
            }
            lock.unlock();
            const double v = log_softmax(n_vocab, logits + i*n_vocab, log_probs.data() + i*nv, tokens[i+1]);
            local_nll += v;
            local_nll2 += v*v;
        }
    };
    for (auto & w : workers) {
        w = std::thread(compute);
    }
    compute();
    for (auto & w : workers) {
        w.join();
    }
    out.write((const char *)log_probs.data(), n_token*nv*sizeof(uint16_t));
}

struct kl_divergence_result {
    double sum_nll  = 0;
    double sum_nll2 = 0;
    double sum_kld  = 0;
    double sum_kld2 = 0;
    double sum_nll_diff  = 0;
    double sum_nll_diff2 = 0;
    size_t n_same_top = 0;
    size_t count = 0;
};

static double log_softmax(int n_vocab, const float * logits, const uint16_t * base_log_prob, int tok, kl_divergence_result & kld) {
    float max_logit = logits[0];
    int imax = 0;
    for (int i = 1; i < n_vocab; ++i) {
        if (logits[i] > max_logit) {
            max_logit = logits[i];
            imax = i;
        }
    }
    double sum_exp = 0.0;
    for (int i = 0; i < n_vocab; ++i) {
        sum_exp += expf(logits[i] - max_logit);
    }
    const float log_sum_exp = log(sum_exp);
    const float * d = (const float *)base_log_prob;
    const float scale = d[0];
    const float min_log_prob = d[1];
    base_log_prob += 4;
    float nll = max_logit + log_sum_exp - logits[tok];
    kld.sum_nll  += nll;
    kld.sum_nll2 += nll*nll;
    nll += (scale*base_log_prob[tok] + min_log_prob);
    kld.sum_nll_diff  += nll;
    kld.sum_nll_diff2 += nll*nll;
    max_logit += log_sum_exp;
    double sum = 0;
    int imax_base = -1;
    float p_log_base_max = 0;
    for (int i = 0; i < n_vocab; ++i) {
        const float p_log_base = scale*base_log_prob[i] + min_log_prob;
        if (i == 0 || p_log_base > p_log_base_max) {
            p_log_base_max = p_log_base;
            imax_base = i;
        }
        if (p_log_base > -16.f) {
            const float p_base = expf(p_log_base);
            sum += p_base * (p_log_base - logits[i] + max_logit);
        }
    }
    kld.sum_kld  += sum;
    kld.sum_kld2 += sum*sum;
    ++kld.count;
    if (imax == imax_base) ++kld.n_same_top;
    return sum;
}

static void process_logits(int n_vocab, const float * logits, const int * tokens, int n_token,
        std::vector<std::thread> & workers, const std::vector<uint16_t> & base_log_probs, kl_divergence_result & kld,
        float * kld_values) {
    std::mutex mutex;
    const int nv = 2*((n_vocab + 1)/2) + 4;
    int counter = 0;
    auto compute = [&mutex, &counter, &base_log_probs, &kld, n_vocab, logits, tokens, n_token, nv, kld_values] () {
        kl_divergence_result local_kld;
        while (true) {
            std::unique_lock<std::mutex> lock(mutex);
            int i = counter++;
            if (i >= n_token) {
                kld.sum_nll  += local_kld.sum_nll;
                kld.sum_nll2 += local_kld.sum_nll2;
                kld.sum_kld  += local_kld.sum_kld;
                kld.sum_kld2 += local_kld.sum_kld2;
                kld.sum_nll_diff  += local_kld.sum_nll_diff;
                kld.sum_nll_diff2 += local_kld.sum_nll_diff2;
                kld.n_same_top += local_kld.n_same_top;
                kld.count += local_kld.count;
                break;
            }
            lock.unlock();
            double v = log_softmax(n_vocab, logits + i*n_vocab, base_log_probs.data() + i*nv, tokens[i+1], local_kld);
            kld_values[i] = (float)v;
        }
    };
    for (auto & w : workers) {
        w = std::thread(compute);
    }
    compute();
    for (auto & w : workers) {
        w.join();
    }
}

static results_perplexity perplexity_v2(llama_context * ctx, const gpt_params & params) {
    // Download: https://s3.amazonaws.com/research.metamind.io/wikitext/wikitext-2-raw-v1.zip?ref=salesforce-research
    // Run `./perplexity -m models/7B/ggml-model-q4_0.bin -f wiki.test.raw`
    // Output: `perplexity: 13.5106 [114/114]`
    // BOS tokens will be added for each chunk before eval

    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));

    fprintf(stderr, "%s: tokenizing the input ..\n", __func__);

    std::vector<llama_token> tokens = ::llama_tokenize(ctx, params.prompt, add_bos);

    const int n_ctx = llama_n_ctx(ctx);

    if (int(tokens.size()) < 2*n_ctx) {
        fprintf(stderr, "%s: you need at least %d tokens to evaluate perplexity with a context of %d\n",__func__,2*n_ctx,
                n_ctx);
        fprintf(stderr, "%s: the data file you provided tokenizes to only %zu tokens\n",__func__,tokens.size());
        return {std::move(tokens), 0., {}, {}};
    }

    std::vector<float> logit_history;
    std::vector<float> prob_history;

    logit_history.resize(tokens.size());
    prob_history.resize(tokens.size());

    if (params.ppl_stride <= 0) {
        fprintf(stderr, "%s: stride is %d but must be greater than zero!\n",__func__,params.ppl_stride);
        return {tokens, -1, logit_history, prob_history};
    }

    const int calc_chunk = n_ctx;

    fprintf(stderr, "%s: have %zu tokens. Calculation chunk = %d\n", __func__, tokens.size(), calc_chunk);

    if (int(tokens.size()) <= calc_chunk) {
        fprintf(stderr, "%s: there are only %zu tokens, this is not enough for a context size of %d and stride %d\n",__func__,
                tokens.size(), n_ctx, params.ppl_stride);
        return {tokens, -1, logit_history, prob_history};
    }

    const int n_chunk_max = (tokens.size() - calc_chunk + params.ppl_stride - 1)  / params.ppl_stride;

    const int n_chunk = params.n_chunks < 0 ? n_chunk_max : std::min(params.n_chunks, n_chunk_max);
    const int n_vocab = llama_n_vocab(llama_get_model(ctx));
    const int n_batch = params.n_batch;

    int count = 0;
    double nll = 0.0;

    fprintf(stderr, "%s: calculating perplexity over %d chunks, batch_size=%d\n", __func__, n_chunk, n_batch);

    for (int i = 0; i < n_chunk; ++i) {
        const int start =     i * params.ppl_stride;
        const int end   = start + calc_chunk;

        const int num_batches = (calc_chunk + n_batch - 1) / n_batch;
        //fprintf(stderr, "%s: evaluating %d...%d using %d batches\n", __func__, start, end, num_batches);

        std::vector<float> logits;

        const auto t_start = std::chrono::high_resolution_clock::now();

        // clear the KV cache
        llama_kv_cache_clear(ctx);

        for (int j = 0; j < num_batches; ++j) {
            const int batch_start = start + j * n_batch;
            const int batch_size  = std::min(end - batch_start, n_batch);

            //fprintf(stderr, "    Batch %d: starts at %d, size is %d, n_past is %d\n",j,batch_start,batch_size,j * n_batch);
            if (llama_decode(ctx, llama_batch_get_one(tokens.data() + batch_start, batch_size, j * n_batch, 0))) {
                //fprintf(stderr, "%s : failed to eval\n", __func__);
                return {tokens, -1, logit_history, prob_history};
            }

            // save original token and restore it after eval
            const auto token_org = tokens[batch_start];

            // add BOS token for the first batch of each chunk
            if (add_bos && j == 0) {
                tokens[batch_start] = llama_token_bos(llama_get_model(ctx));
            }

            const auto batch_logits = llama_get_logits(ctx);
            logits.insert(logits.end(), batch_logits, batch_logits + batch_size * n_vocab);

            if (j == 0) {
                tokens[batch_start] = token_org;
            }
        }

        const auto t_end = std::chrono::high_resolution_clock::now();

        if (i == 0) {
            const float t_total = std::chrono::duration<float>(t_end - t_start).count();
            fprintf(stderr, "%s: %.2f seconds per pass - ETA ", __func__, t_total);
            int total_seconds = (int)(t_total * n_chunk);
            if (total_seconds >= 60*60) {
                fprintf(stderr, "%d hours ", total_seconds / (60*60));
                total_seconds = total_seconds % (60*60);
            }
            fprintf(stderr, "%.2f minutes\n", total_seconds / 60.0);
        }

        //fprintf(stderr, "%s: using tokens %d...%d\n",__func__,params.n_ctx - params.ppl_stride + start, params.n_ctx + start);
        for (int j = n_ctx - params.ppl_stride - 1; j < n_ctx - 1; ++j) {

            // Calculate probability of next token, given the previous ones.
            const std::vector<float> tok_logits(
                logits.begin() + (j + 0) * n_vocab,
                logits.begin() + (j + 1) * n_vocab);

            const float prob = softmax(tok_logits)[tokens[start + j + 1]];
            logit_history[start + j + 1] = tok_logits[tokens[start + j + 1]];
            prob_history[start + j + 1]  = prob;

            nll += -std::log(prob);
            ++count;
        }
        // perplexity is e^(average negative log-likelihood)
        if (params.ppl_output_type == 0) {
            printf("[%d]%.4lf,", i + 1, std::exp(nll / count));
        } else {
            printf("%8d  %.4lf\n", i*params.ppl_stride, std::exp(nll / count));
        }
        fflush(stdout);
    }
    printf("\n");

    return {tokens, std::exp(nll / count), logit_history, prob_history};
}

static results_perplexity perplexity(llama_context * ctx, const gpt_params & params) {
    if (params.ppl_stride > 0) {
        return perplexity_v2(ctx, params);
    }

    // Download: https://s3.amazonaws.com/research.metamind.io/wikitext/wikitext-2-raw-v1.zip?ref=salesforce-research
    // Run `./perplexity -m models/7B/ggml-model-q4_0.bin -f wiki.test.raw`
    // Output: `perplexity: 13.5106 [114/114]`
    // BOS tokens will be added for each chunk before eval

    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));
    const int n_ctx = llama_n_ctx(ctx);

    std::ofstream logits_stream;
    if (!params.logits_file.empty()) {
        logits_stream.open(params.logits_file.c_str());
        if (!logits_stream.is_open()) {
            fprintf(stderr, "%s: failed to open %s for writing\n", __func__, params.logits_file.c_str());
            return {};
        }
        fprintf(stderr, "%s: saving all logits to %s\n", __func__, params.logits_file.c_str());
        logits_stream.write("_logits_", 8);
        logits_stream.write((const char *)&n_ctx, sizeof(n_ctx));
    }

    auto tim1 = std::chrono::high_resolution_clock::now();
    fprintf(stderr, "%s: tokenizing the input ..\n", __func__);

    std::vector<llama_token> tokens = ::llama_tokenize(ctx, params.prompt, add_bos);

    auto tim2 = std::chrono::high_resolution_clock::now();
    fprintf(stderr, "%s: tokenization took %g ms\n",__func__,1e-3*std::chrono::duration_cast<std::chrono::microseconds>(tim2-tim1).count());

    if (int(tokens.size()) < 2*n_ctx) {
        fprintf(stderr, "%s: you need at least %d tokens to evaluate perplexity with a context of %d\n",__func__,2*n_ctx,
                n_ctx);
        fprintf(stderr, "%s: the data file you provided tokenizes to only %zu tokens\n",__func__,tokens.size());
        return {std::move(tokens), 0., {}, {}};
    }

    std::vector<float> logit_history;
    logit_history.resize(tokens.size());

    std::vector<float> prob_history;
    prob_history.resize(tokens.size());

    const int n_chunk_max = tokens.size() / n_ctx;

    const int n_chunk = params.n_chunks < 0 ? n_chunk_max : std::min(params.n_chunks, n_chunk_max);
    const int n_vocab = llama_n_vocab(llama_get_model(ctx));
    const int n_batch = params.n_batch;

    int count = 0;
    double nll = 0.0;
    double nll2 = 0.0;

    const int num_batches = (n_ctx + n_batch - 1) / n_batch;

    std::vector<float> logits;
    if (num_batches > 1) {
        logits.reserve((size_t)n_ctx * n_vocab);
    }

    fprintf(stderr, "%s: calculating perplexity over %d chunks, batch_size=%d\n", __func__, n_chunk, n_batch);

    std::vector<std::thread> workers(std::thread::hardware_concurrency() - 1);

    std::vector<uint16_t> log_probs;
    if (!params.logits_file.empty()) {
        logits_stream.write((const char *)&n_vocab, sizeof(n_vocab));
        logits_stream.write((const char *)&n_chunk, sizeof(n_chunk));
        logits_stream.write((const char *)tokens.data(), n_chunk*n_ctx*sizeof(tokens[0]));
        const int nv = 2*((n_vocab + 1)/2) + 4;
        log_probs.resize(n_ctx * nv);
    }

    for (int i = 0; i < n_chunk; ++i) {
        const int start =     i * n_ctx;
        const int end   = start + n_ctx;

        const auto t_start = std::chrono::high_resolution_clock::now();

        // clear the KV cache
        llama_kv_cache_clear(ctx);

        for (int j = 0; j < num_batches; ++j) {
            const int batch_start = start + j * n_batch;
            const int batch_size  = std::min(end - batch_start, n_batch);

            // save original token and restore it after eval
            const auto token_org = tokens[batch_start];

            // add BOS token for the first batch of each chunk
            if (add_bos && j == 0) {
                tokens[batch_start] = llama_token_bos(llama_get_model(ctx));
            }

            if (llama_decode(ctx, llama_batch_get_one(tokens.data() + batch_start, batch_size, j * n_batch, 0))) {
                fprintf(stderr, "%s : failed to eval\n", __func__);
                return {tokens, -1, logit_history, prob_history};
            }

            // restore the original token in case it was set to BOS
            tokens[batch_start] = token_org;

            if (num_batches > 1) {
                const auto * batch_logits = llama_get_logits(ctx);
                logits.insert(logits.end(), batch_logits, batch_logits + batch_size * n_vocab);
            }
        }

        const auto t_end = std::chrono::high_resolution_clock::now();

        if (i == 0) {
            const float t_total = std::chrono::duration<float>(t_end - t_start).count();
            fprintf(stderr, "%s: %.2f seconds per pass - ETA ", __func__, t_total);
            int total_seconds = (int)(t_total * n_chunk);
            if (total_seconds >= 60*60) {
                fprintf(stderr, "%d hours ", total_seconds / (60*60));
                total_seconds = total_seconds % (60*60);
            }
            fprintf(stderr, "%.2f minutes\n", total_seconds / 60.0);
        }

        // We get the logits for all the tokens in the context window (params.n_ctx)
        // from llama_eval above.  Now, based on https://huggingface.co/docs/transformers/perplexity,
        // calculate the perplexity over the last half of the window (so the model always has
        // some context to predict the token).
        //
        // We rely on the fact that attention in the forward pass only looks at previous
        // tokens here, so the logits returned for each token are an accurate representation
        // of what the model would have predicted at that point.
        //
        // Example, we have a context window of 512, we will compute perplexity for each of the
        // last 256 tokens.  Then, we split the input up into context window size chunks to
        // process the entire prompt.
        const int first = n_ctx/2;
        const float * all_logits = num_batches > 1 ? logits.data() : llama_get_logits(ctx);
        if (!params.logits_file.empty()) {
            process_logits(logits_stream, n_vocab, all_logits + first*n_vocab, tokens.data() + start + first, n_ctx - 1 - first,
                    workers, log_probs, nll, nll2);
        } else {
            process_logits(n_vocab, all_logits + first*n_vocab, tokens.data() + start + first, n_ctx - 1 - first,
                    workers, nll, nll2, logit_history.data() + start + first, prob_history.data() + start + first);
        }
        count += n_ctx - first - 1;

        // perplexity is e^(average negative log-likelihood)
        if (params.ppl_output_type == 0) {
            printf("[%d]%.4lf,", i + 1, std::exp(nll / count));
        } else {
            double av = nll/count;
            double av2 = nll2/count - av*av;
            if (av2 > 0) av2 = sqrt(av2/(count-1));
            printf("%8d  %.4lf  %4lf  %4lf\n", i*n_ctx, std::exp(nll / count), av, av2);
        }
        fflush(stdout);

        logits.clear();
    }
    printf("\n");

    nll2 /= count;
    nll /= count;
    const double ppl = exp(nll);
    nll2 -= nll * nll;
    if (nll2 > 0) {
        nll2 = sqrt(nll2/(count-1));
        printf("Final estimate: PPL = %.4lf +/- %.5lf\n", ppl, nll2*ppl);
    } else {
        printf("Unexpected negative standard deviation of log(prob)\n");
    }

    return {tokens, ppl, logit_history, prob_history};
}

static bool decode_helper(llama_context * ctx, llama_batch & batch, std::vector<float> & batch_logits, int32_t n_batch, int32_t n_vocab) {
    for (int32_t i = 0; i < (int32_t) batch.n_tokens; i += n_batch) {
        const int32_t n_tokens = std::min(n_batch, (int32_t) (batch.n_tokens - i));

        llama_batch batch_view = {
            n_tokens,
            batch.token    + i,
            nullptr,
            batch.pos      + i,
            batch.n_seq_id + i,
            batch.seq_id   + i,
            batch.logits   + i,
            0, 0, 0, // unused
        };

        const int ret = llama_decode(ctx, batch_view);
        if (ret != 0) {
            LOG_TEE("failed to decode the batch, n_batch = %d, ret = %d\n", n_batch, ret);
            return false;
        }

        memcpy(batch_logits.data() + i*n_vocab, llama_get_logits(ctx), n_tokens*n_vocab*sizeof(float));
    }

    return true;
}

#define K_TOKEN_CHUNK 4

static void compute_logprobs(const float * batch_logits, int n_vocab, std::vector<std::thread>& workers,
        const std::vector<std::pair<size_t, llama_token>>& eval_pairs, std::vector<float>& eval_results) {
    if (eval_results.size() != eval_pairs.size()) {
        eval_results.resize(eval_pairs.size());
    }
    if (eval_pairs.empty()) return;

    size_t max_threads = std::min((eval_pairs.size() + K_TOKEN_CHUNK - 1)/K_TOKEN_CHUNK, workers.size());

    std::atomic<int> counter(0);
    auto compute = [&counter, &eval_pairs, &eval_results, batch_logits, n_vocab] () {
        float local_logprobs[K_TOKEN_CHUNK];
        while (true) {
            size_t first = counter.fetch_add(K_TOKEN_CHUNK, std::memory_order_relaxed);
            if (first >= eval_results.size()) break;
            size_t last = std::min(first + K_TOKEN_CHUNK, eval_results.size());
            for (size_t i = first; i < last; ++i) {
                auto logits = batch_logits + eval_pairs[i].first * n_vocab;
                float max_logit = logits[0];
                for (int j = 1; j < n_vocab; ++j) {
                    max_logit = std::max(max_logit, logits[j]);
                }
                float sum_p = 0.f;
                for (int j = 0; j < n_vocab; ++j) {
                    sum_p += expf(logits[j] - max_logit);
                }
                local_logprobs[i - first] = logits[eval_pairs[i].second] - max_logit - std::log(sum_p);
            }
            std::memcpy(eval_results.data() + first, local_logprobs, (last - first)*sizeof(float));
        }
    };

    for (size_t it = 0; it < max_threads; ++it) {
        workers[it] = std::thread(compute);
    }
    for (size_t it = 0; it < max_threads; ++it) {
        workers[it].join();
    }
}

static void hellaswag_score(llama_context * ctx, const gpt_params & params) {
    // Calculates hellaswag score (acc_norm) from prompt
    //
    // Data extracted from the HellaSwag validation dataset (MIT license) https://github.com/rowanz/hellaswag/blob/master/data/hellaswag_val.jsonl
    // All used data fields are preprocessed as in https://github.com/EleutherAI/lm-evaluation-harness/blob/df3da98c5405deafd519c2ddca52bb7c3fe36bef/lm_eval/tasks/hellaswag.py#L62-L68
    //
    // All 10042 tasks should be extracted to keep the results standardized like other implementations.
    //
    // Datafile layout:
    // ['??'] denotes json fields
    // 6 lines per task:
    // ['activity_label'] + ": " +['ctx']  - The first part of the query, the context
    // ['label'] - The index the best common sense ending aka gold ending
    // ['endings'][0] - Endings added to the first part of the query
    // ['endings'][1]
    // ['endings'][2]
    // ['endings'][3]

    std::vector<std::string> prompt_lines;
    std::istringstream strstream(params.prompt);
    std::string line;

    while (std::getline(strstream,line,'\n')) {
        prompt_lines.push_back(line);
    }

    if (prompt_lines.size() % 6 != 0) {
        fprintf(stderr, "%s : number of lines in prompt not a multiple of 6.\n", __func__);
        return;
    }

    size_t hs_task_count = prompt_lines.size()/6;
    fprintf(stderr, "%s : loaded %zu tasks from prompt.\n", __func__, hs_task_count);

    const bool is_spm = llama_vocab_type(llama_get_model(ctx)) == LLAMA_VOCAB_TYPE_SPM;
    fprintf(stderr, "================================= is_spm = %d\n", is_spm);

    // This is needed as usual for LLaMA models
    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));

    // The tasks should be randomized so the score stabilizes quickly.
    bool randomize_tasks = true;

    // Number of tasks to use when computing the score
    if (params.hellaswag_tasks < hs_task_count) {
        hs_task_count = params.hellaswag_tasks;
    }

    // The random seed should not impact the final result if the computation is done over enough tasks, so kept hardcoded for now
    std::mt19937 rng(1);

    // Dataholder for hellaswag tasks
    struct hs_data_t {
        std::string context;
        size_t gold_ending_idx;
        std::string ending[4];
        size_t ending_logprob_count[4];
        double ending_logprob[4];

        size_t i_batch;         // starting index in the llama_batch
        size_t common_prefix;   // max number of initial tokens that are the same in all sentences
        size_t required_tokens; // needed number of tokens to evaluate all 4 endings
        std::vector<llama_token> seq_tokens[4];
    };

    fprintf(stderr, "%s : selecting %zu %s tasks.\n", __func__, hs_task_count, (randomize_tasks?"randomized":"the first")  );

    // Select and read data from prompt lines
    std::vector<hs_data_t> hs_data(hs_task_count);
    for (size_t i = 0; i < hs_task_count; i++) {
        size_t idx = i;

        auto & hs_cur = hs_data[i];

        // Select a random example of those left in the prompt
        if (randomize_tasks) {
            std::uniform_int_distribution<size_t> dist(0, prompt_lines.size()/6-1 ) ;
            idx = dist(rng);
        }

        hs_cur.context = prompt_lines[idx*6];
        hs_cur.gold_ending_idx = std::stoi( prompt_lines[idx*6+1] );
        for (size_t j = 0; j < 4; j++) {
            hs_cur.ending[j] = prompt_lines[idx*6+2+j];
            hs_cur.seq_tokens[j] = ::llama_tokenize(ctx, hs_cur.context + " " + hs_cur.ending[j], add_bos);
        }

        // determine the common prefix of the endings
        hs_cur.common_prefix = 0;
        for (size_t k = 0; k < hs_cur.seq_tokens[0].size(); k++) {
            if (hs_cur.seq_tokens[0][k] != hs_cur.seq_tokens[1][k] ||
                hs_cur.seq_tokens[0][k] != hs_cur.seq_tokens[2][k] ||
                hs_cur.seq_tokens[0][k] != hs_cur.seq_tokens[3][k]) {
                break;
            }
            hs_cur.common_prefix++;
        }
        hs_cur.required_tokens = hs_cur.common_prefix +
            hs_cur.seq_tokens[0].size() - hs_cur.common_prefix +
            hs_cur.seq_tokens[1].size() - hs_cur.common_prefix +
            hs_cur.seq_tokens[2].size() - hs_cur.common_prefix +
            hs_cur.seq_tokens[3].size() - hs_cur.common_prefix;

        //GGML_ASSERT(hs_cur.common_prefix >= ::llama_tokenize(ctx, hs_cur.context, add_bos).size());

        // Delete the selected random example from the prompt
        if (randomize_tasks) {
            prompt_lines.erase( std::next(prompt_lines.begin(),idx*6)  , std::next(prompt_lines.begin(),idx*6+6) );
        }
    }

    fprintf(stderr, "%s : calculating hellaswag score over selected tasks.\n", __func__);

    printf("\ntask\tacc_norm\n");

    double acc = 0.0f;

    const int n_vocab = llama_n_vocab(llama_get_model(ctx));
    const int n_ctx   = llama_n_ctx(ctx);
    const int n_batch = params.n_batch;

    const int max_tasks_per_batch = 32;
    const int max_seq = 4*max_tasks_per_batch;

    llama_batch batch = llama_batch_init(n_ctx, 0, max_seq);

    std::vector<float> tok_logits(n_vocab);
    std::vector<float> batch_logits(n_vocab*n_ctx);

    std::vector<std::pair<size_t, llama_token>> eval_pairs;
    std::vector<float> eval_results;
    std::vector<std::thread> workers(std::thread::hardware_concurrency());

    for (size_t i0 = 0; i0 < hs_task_count; i0++) {
        int n_cur = 0;

        size_t i1 = i0;
        size_t i_batch = 0; // this tells us where in `llama_batch` we are currently

        llama_batch_clear(batch);

        // batch as much tasks as possible into the available context
        // each task has 4 unique seuqnce ids - one for each ending
        // the common prefix is shared among the 4 sequences to save tokens
        // we extract logits only from the last common token and from all ending tokens of each sequence
        while (n_cur + (int) hs_data[i1].required_tokens <= n_ctx) {
            auto & hs_cur = hs_data[i1];

            const int s0 = 4*(i1 - i0);
            if (s0 + 4 > max_seq) {
                break;
            }

            for (size_t i = 0; i < hs_cur.common_prefix; ++i) {
                llama_batch_add(batch, hs_cur.seq_tokens[0][i], i, { s0 + 0, s0 + 1, s0 + 2, s0 + 3}, false);
            }
            batch.logits[batch.n_tokens - 1] = true; // we need logits for the last token of the common prefix

            for (int s = 0; s < 4; ++s) {
                for (size_t i = hs_cur.common_prefix; i < hs_cur.seq_tokens[s].size(); ++i) {
                    llama_batch_add(batch, hs_cur.seq_tokens[s][i], i, { s0 + s }, true);
                }
            }

            hs_cur.i_batch = i_batch;
            i_batch += hs_cur.required_tokens;

            n_cur += hs_data[i1].required_tokens;
            if (++i1 == hs_task_count) {
                break;
            }
        }

        if (i0 == i1) {
            fprintf(stderr, "%s : task %zu does not fit in the context window\n", __func__, i0);
            return;
        }

        llama_kv_cache_clear(ctx);

        // decode all tasks [i0, i1)
        if (!decode_helper(ctx, batch, batch_logits, n_batch, n_vocab)) {
            fprintf(stderr, "%s: llama_decode() failed\n", __func__);
            return;
        }

        // Compute log-probs in parallel
        // First we collect all tasks
        eval_pairs.clear();
        for (size_t i = i0; i < i1; ++i) {
            auto & hs_cur = hs_data[i];
            size_t li = hs_cur.common_prefix;
            for (int s = 0; s < 4; ++s) {
                for (size_t j = hs_cur.common_prefix; j < hs_cur.seq_tokens[s].size() - 1; j++) {
                    eval_pairs.push_back(std::make_pair(hs_cur.i_batch + li++, hs_cur.seq_tokens[s][j + 1]));
                }
                ++li;
            }
        }
        // Then we do the actual calculation
        compute_logprobs(batch_logits.data(), n_vocab, workers, eval_pairs, eval_results);

        size_t ir = 0;

        // compute the logprobs for each ending of the decoded tasks
        for (size_t i = i0; i < i1; ++i) {
            auto & hs_cur = hs_data[i];

            std::memcpy(tok_logits.data(), batch_logits.data() + n_vocab*(hs_cur.i_batch + hs_cur.common_prefix - 1), n_vocab*sizeof(float));

            const auto first_probs = softmax(tok_logits);

            for (int s = 0; s < 4; ++s) {
                hs_cur.ending_logprob_count[s] = 1;
                hs_cur.ending_logprob[s] = std::log(first_probs[hs_cur.seq_tokens[s][hs_cur.common_prefix]]);
                for (size_t j = hs_cur.common_prefix; j < hs_cur.seq_tokens[s].size() - 1; j++) {
                    hs_cur.ending_logprob[s] += eval_results[ir++];
                    hs_cur.ending_logprob_count[s]++;
                }
                hs_cur.ending_logprob[s] /= hs_cur.ending_logprob_count[s];
            }

            // Find the ending with maximum logprob
            size_t ending_logprob_max_idx = 0;
            double ending_logprob_max_val = hs_cur.ending_logprob[0];
            for (size_t s = 1; s < 4; s++) {
                if (hs_cur.ending_logprob[s] > ending_logprob_max_val) {
                    ending_logprob_max_idx = s;
                    ending_logprob_max_val =  hs_cur.ending_logprob[s];
                }
            }

            //printf("max logprob ending idx %lu, gold ending idx %lu\n", ending_logprob_max_idx, hs_cur.gold_ending_idx);

            // If the gold ending got the maximum logprobe add one accuracy point
            if (ending_logprob_max_idx == hs_cur.gold_ending_idx) {
                acc += 1.0;
            }

            // Print the accumulated accuracy mean x 100
            printf("%zu\t%.8lf\n", i + 1, acc/double(i + 1)*100.0);
            fflush(stdout);
        }

        i0 = i1 - 1;
    }

    llama_batch_free(batch);

    printf("\n");
}

struct winogrande_entry {
    std::string first;
    std::string second;
    std::array<std::string, 2> choices;
    int answer;

    size_t i_batch;
    size_t common_prefix;
    size_t required_tokens;
    size_t n_base1; // number of tokens for context + choice 1
    size_t n_base2; // number of tokens for context + choice 2
    std::vector<llama_token> seq_tokens[2];
};

static std::vector<winogrande_entry> load_winogrande_from_csv(const std::string& prompt) {
    std::vector<winogrande_entry> result;
    std::istringstream in(prompt);
    std::string line;
    std::array<int, 4> comma_pos;
    while (true) {
        std::getline(in, line);
        if (in.fail() || in.eof()) break;
        int ipos = 0;
        bool quote_open = false;
        for (int i = 0; i < int(line.size()); ++i) {
            if (!quote_open) {
                if (line[i] == ',') {
                    comma_pos[ipos++] = i;
                    if (ipos == 4) break;
                }
                else if (line[i] == '"') {
                    quote_open = true;
                }
            }
            else {
                if (line[i] == '"') {
                    quote_open = false;
                }
            }
        }
        if (ipos != 4) {
            printf("%s: failed to find comma separators in <%s>\n", __func__, line.c_str());
            continue;
        }
        auto sentence = line[comma_pos[0]+1] == '"' ? line.substr(comma_pos[0]+2, comma_pos[1] - comma_pos[0] - 3)
                                                    : line.substr(comma_pos[0]+1, comma_pos[1] - comma_pos[0] - 1);
        auto choice1 = line.substr(comma_pos[1]+1, comma_pos[2] - comma_pos[1] - 1);
        auto choice2 = line.substr(comma_pos[2]+1, comma_pos[3] - comma_pos[2] - 1);
        auto answer  = line.substr(comma_pos[3]+1, line.size() - comma_pos[3] - 1);
        auto index = line.substr(0, comma_pos[0]);
        int where = 0;
        for ( ; where < int(sentence.size()); ++where) {
            if (sentence[where] == '_') break;
        }
        if (where == int(sentence.size())) {
            printf("%s: no _ in <%s>\n", __func__, sentence.c_str());
            continue;
        }
        std::istringstream stream(answer.c_str());
        int i_answer; stream >> i_answer;
        if (stream.fail() || i_answer < 1 || i_answer > 2) {
            printf("%s: failed to parse answer <%s>\n", __func__, answer.c_str());
            continue;
        }
        result.emplace_back();
        auto& wg = result.back();
        wg.first = sentence.substr(0, where);
        wg.second = sentence.substr(where + 1, sentence.size() - where - 1);
        wg.choices[0] = std::move(choice1);
        wg.choices[1] = std::move(choice2);
        wg.answer = i_answer;
    }
    return result;
}

/*
 * Evaluates the Winogrande score.
 * Uses a CSV containing task index, dentence, choice 1, choice 2, answer (1 or 2)
 * You can get one such dataset from e.g. https://huggingface.co/datasets/ikawrakow/winogrande-eval-for-llama.cpp
 * As an example, the 1st row in the above dataset is
 *
 *    0,Sarah was a much better surgeon than Maria so _ always got the easier cases.,Sarah,Maria,2
 *
 */
static void winogrande_score(llama_context * ctx, const gpt_params & params) {

    constexpr int k_min_trailing_ctx = 3;

    auto data = load_winogrande_from_csv(params.prompt);
    if (data.empty()) {
        fprintf(stderr, "%s: no tasks\n", __func__);
        return;
    }

    fprintf(stderr, "%s : loaded %zu tasks from prompt.\n", __func__, data.size());

    if (params.winogrande_tasks > 0 && params.winogrande_tasks < data.size()) {
        fprintf(stderr, "%s : selecting %zu random tasks\n", __func__, params.winogrande_tasks);
        std::mt19937 rng(1);
        std::vector<int> aux(data.size());
        for (int i = 0; i < int(data.size()); ++i) {
            aux[i] = i;
        }
        float scale = 1/(1.f + (float)rng.max());
        std::vector<winogrande_entry> selected;
        selected.resize(params.winogrande_tasks);
        for (int i = 0; i < int(params.winogrande_tasks); ++i) {
            int j = int(scale*rng()*aux.size());
            selected[i] = std::move(data[aux[j]]);
            aux[j] = aux.back();
            aux.pop_back();
        }
        data = std::move(selected);
    }

    fprintf(stderr, "%s : tokenizing selected tasks\n", __func__);

    // This is needed as usual for LLaMA models
    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));

    for (auto & task : data) {
        task.seq_tokens[0] = ::llama_tokenize(ctx, task.first + task.choices[0] + task.second, add_bos);
        task.seq_tokens[1] = ::llama_tokenize(ctx, task.first + task.choices[1] + task.second, add_bos);

        task.common_prefix = 0;
        for (size_t k = 0; k < task.seq_tokens[0].size(); k++) {
            if (task.seq_tokens[0][k] != task.seq_tokens[1][k]) {
                break;
            }
            task.common_prefix++;
        }

        task.required_tokens = task.common_prefix +
            task.seq_tokens[0].size() - task.common_prefix +
            task.seq_tokens[1].size() - task.common_prefix;

        task.n_base1 = ::llama_tokenize(ctx, task.first + task.choices[0], add_bos).size();
        task.n_base2 = ::llama_tokenize(ctx, task.first + task.choices[1], add_bos).size();
    }

    fprintf(stderr, "%s : calculating winogrande score over selected tasks.\n", __func__);

    const int n_vocab = llama_n_vocab(llama_get_model(ctx));
    const int n_ctx   = llama_n_ctx(ctx);
    const int n_batch = params.n_batch;

    const int max_tasks_per_batch = 128;
    const int max_seq = 2*max_tasks_per_batch;

    llama_batch batch = llama_batch_init(n_ctx, 0, max_seq);

    std::vector<float> tok_logits(n_vocab);
    std::vector<float> batch_logits(n_vocab*n_ctx);

    std::vector<std::pair<size_t, llama_token>> eval_pairs;
    std::vector<float> eval_results;
    std::vector<std::thread> workers(std::thread::hardware_concurrency());

    int n_correct = 0;
    int n_done    = 0;

    for (size_t i0 = 0; i0 < data.size(); i0++) {
        int n_cur = 0;

        size_t i1 = i0;
        size_t i_batch = 0;

        llama_batch_clear(batch);

        while (n_cur + (int) data[i1].required_tokens <= n_ctx) {
            const int s0 = 2*(i1 - i0);
            if (s0 + 2 > max_seq) {
                break;
            }

            for (size_t i = 0; i < data[i1].common_prefix; ++i) {
                llama_batch_add(batch, data[i1].seq_tokens[0][i], i, { s0 + 0, s0 + 1}, false);
            }
            batch.logits[batch.n_tokens - 1] = true;

            for (int s = 0; s < 2; ++s) {
                for (size_t i = data[i1].common_prefix; i < data[i1].seq_tokens[s].size(); ++i) {
                    llama_batch_add(batch, data[i1].seq_tokens[s][i], i, { s0 + s }, true);
                }
            }

            data[i1].i_batch = i_batch;
            i_batch += data[i1].required_tokens;

            n_cur += data[i1].required_tokens;
            if (++i1 == data.size()) {
                break;
            }
        }

        if (i0 == i1) {
            fprintf(stderr, "%s : task %zu does not fit in the context window\n", __func__, i0);
            return;
        }

        llama_kv_cache_clear(ctx);

        // decode all tasks [i0, i1)
        if (!decode_helper(ctx, batch, batch_logits, n_batch, n_vocab)) {
            fprintf(stderr, "%s: llama_decode() failed\n", __func__);
            return;
        }

        eval_pairs.clear();
        for (size_t i = i0; i < i1; ++i) {
            auto & task = data[i];

            const bool skip_choice =
                task.seq_tokens[0].size() - task.common_prefix > k_min_trailing_ctx &&
                task.seq_tokens[1].size() - task.common_prefix > k_min_trailing_ctx;

            const auto& n_base1 = skip_choice ? task.n_base1 : task.common_prefix;
            const int last_1st = task.seq_tokens[0].size() - n_base1 > 1 ? 1 : 0;
            size_t li = n_base1 - 1;
            for (size_t j = n_base1-1; j < task.seq_tokens[0].size()-1-last_1st; ++j) {
                eval_pairs.push_back(std::make_pair(task.i_batch + li++, task.seq_tokens[0][j+1]));
            }
            const auto& n_base2 = skip_choice ? task.n_base2 : task.common_prefix;
            const int last_2nd = task.seq_tokens[1].size() - n_base2 > 1 ? 1 : 0;
            li = task.seq_tokens[0].size() - task.common_prefix + n_base2 - 1;
            for (size_t j = n_base2-1; j < task.seq_tokens[1].size()-1-last_2nd; ++j) {
                eval_pairs.push_back(std::make_pair(task.i_batch + li++, task.seq_tokens[1][j+1]));
            }
        }
        compute_logprobs(batch_logits.data(), n_vocab, workers, eval_pairs, eval_results);

        size_t ir = 0;
        for (size_t i = i0; i < i1; ++i) {
            auto & task = data[i];

            const bool skip_choice =
                task.seq_tokens[0].size() - task.common_prefix > k_min_trailing_ctx &&
                task.seq_tokens[1].size() - task.common_prefix > k_min_trailing_ctx;

            float score_1st = 0;
            const auto& n_base1 = skip_choice ? task.n_base1 : task.common_prefix;
            const int last_1st = task.seq_tokens[0].size() - n_base1 > 1 ? 1 : 0;
            for (size_t j = n_base1-1; j < task.seq_tokens[0].size()-1-last_1st; ++j) {
                score_1st += eval_results[ir++];
            }
            score_1st /= (task.seq_tokens[0].size() - n_base1 - last_1st);

            float score_2nd = 0;
            const auto& n_base2 = skip_choice ? task.n_base2 : task.common_prefix;
            const int last_2nd = task.seq_tokens[1].size() - n_base2 > 1 ? 1 : 0;
            for (size_t j = n_base2-1; j < task.seq_tokens[1].size()-1-last_2nd; ++j) {
                score_2nd += eval_results[ir++];
            }
            score_2nd /= (task.seq_tokens[1].size() - n_base2 - last_2nd);

            int result = score_1st > score_2nd ? 1 : 2;

            if (result == task.answer) {
                ++n_correct;
            }
            ++n_done;

            // print the accumulated accuracy mean x 100
            printf("%zu\t%.4lf\t%10.6f  %10.6f  %d  %d\n", i+1, 100.0 * n_correct/n_done, score_1st, score_2nd, result, task.answer);
            fflush(stdout);
        }

        i0 = i1 - 1;
    }

    printf("\n");

    if (n_done < 100) return;

    const float p = 1.f*n_correct/n_done;
    const float sigma = 100.f*sqrt(p*(1-p)/(n_done-1));
    printf("Final Winogrande score(%d tasks): %.4lf +/- %.4lf\n", n_done, 100*p, sigma);
}

static bool deserialize_string(std::istream & in, std::string & str) {
    uint32_t size;
    if (!in.read((char *)&size, sizeof(size)).fail()) {
        str.resize(size);
        if (!in.read((char *)&str[0], size).fail()) return true;
    }
    return false;
}

struct multiple_choice_answers {
    std::vector<std::string> answers;
    std::vector<int>         labels;
    bool deserialize(std::istream& in) {
        uint32_t n;
        in.read((char *)&n, sizeof(n));
        if (in.fail() || n > 100) return false; // 100 as max. number of answers should be good enough for any practical purpose
        answers.resize(n);
        labels.resize(n);
        for (auto& a : answers) {
            if (!deserialize_string(in, a)) return false;
        }
        in.read((char *)labels.data(), n*sizeof(int));
        return !in.fail();
    }
};

struct multiple_choice_task {
    std::string question;         // the question (or context that needs to be continued)
    multiple_choice_answers mc1;  // possible answers (continuations) with a single correct answer
    multiple_choice_answers mc2;  // possible answers (continuations) with multiple correct answers - not handled yet
    bool deserialize(std::istream& in) {
        if (!deserialize_string(in, question)) return false;
        return mc1.deserialize(in) && mc2.deserialize(in);
    }

    // For evaluation
    size_t i_batch;         // starting index in the llama_batch
    size_t common_prefix;   // max number of initial tokens that are the same in all sentences
    size_t required_tokens; // needed number of tokens to evaluate all answers
    std::vector<std::vector<llama_token>> seq_tokens;
    std::vector<float> log_probs;
};

static bool multiple_choice_prepare_one_task(llama_context * ctx, bool add_bos, multiple_choice_task& task, bool log_error) {
    if (task.question.empty() || task.mc1.answers.empty()) {
        if (log_error) {
            printf("%s: found bad task with empty question and/or answers\n", __func__);
        }
        return false;
    }
    task.seq_tokens.reserve(task.mc1.answers.size());
    for (auto& answer : task.mc1.answers) {
        if (answer.empty()) {
            if (log_error) {
                printf("%s: found empty answer\n", __func__);
            }
            return false;
        }
        task.seq_tokens.emplace_back(::llama_tokenize(ctx, task.question + " " + answer, add_bos));
    }
    auto min_len = task.seq_tokens.front().size();
    for (auto& seq : task.seq_tokens) {
        min_len = std::min(min_len, seq.size());
    }
    task.common_prefix = 0;
    for (size_t k = 0; k < min_len; ++k) {
        auto token = task.seq_tokens[0][k];
        bool all_same = true;
        for (size_t i = 1; i < task.seq_tokens.size(); ++i) {
            if (task.seq_tokens[i][k] != token) {
                all_same = false;
                break;
            }
        }
        if (!all_same) {
            break;
        }
        ++task.common_prefix;
    }
    task.required_tokens = task.common_prefix;
    for (auto& seq : task.seq_tokens) {
        task.required_tokens += seq.size() - task.common_prefix;
    }
    return true;
}

//
// Calculates score for multiple choice tasks with single correct answer from prompt.
// Commonly used LLM evaluation metrics of this type are
//   * ARC
//   * HellaSwag
//   * MMLU
//   * TruthfulQA
//
// Validation datasets for these 4 tests can be found at
//     https://huggingface.co/datasets/ikawrakow/validation-datasets-for-llama.cpp
// The data for these datasets was extracted from
//     git@hf.co:datasets/allenai/ai2_arc
//     https://github.com/rowanz/hellaswag/blob/master/data/hellaswag_val.jsonl
//     git@hf.co:datasets/Stevross/mmlu
//     https://huggingface.co/datasets/truthful_qa
//
static void multiple_choice_score(llama_context * ctx, const gpt_params & params) {

    std::istringstream strstream(params.prompt);
    uint32_t n_task;
    strstream.read((char *)&n_task, sizeof(n_task));
    if (strstream.fail() || n_task == 0) {
        printf("%s: no tasks\n", __func__);
        return;
    }
    printf("%s: there are %u tasks in prompt\n", __func__, n_task);
    std::vector<uint32_t> task_pos(n_task);
    strstream.read((char *)task_pos.data(), task_pos.size()*sizeof(uint32_t));
    if (strstream.fail()) {
        printf("%s: failed to raad task positions from prompt\n", __func__);
        return;
    }

    std::vector<multiple_choice_task> tasks;
    if (params.multiple_choice_tasks == 0 || params.multiple_choice_tasks >= (size_t)n_task) {
        // Use all tasks
        tasks.resize(n_task);
        printf("%s: reading tasks", __func__);
        int n_dot = n_task/100;
        int i = 0;
        for (auto& task : tasks) {
            ++i;
            if (!task.deserialize(strstream)) {
                printf("%s: failed to read task %d of %u\n", __func__, i, n_task);
                return;
            }
            if (i%n_dot == 0) printf(".");
        }
        printf("done\n");
    }
    else {
        printf("%s: selecting %zu random tasks from %u tasks available\n", __func__, params.multiple_choice_tasks, n_task);
        std::mt19937 rng(1);
        std::vector<int> aux(n_task);
        for (uint32_t i = 0; i < n_task; ++i) aux[i] = i;
        float scale = 1.f/(1.f + (float)std::mt19937::max());
        tasks.resize(params.multiple_choice_tasks);
        for (auto& task : tasks) {
            int j = (int)(scale * rng() * aux.size());
            int idx = aux[j];
            aux[j] = aux.back();
            aux.pop_back();
            strstream.seekg(task_pos[idx], std::ios::beg);
            if (!task.deserialize(strstream)) {
                printf("%s: failed to read task %d at position %u\n", __func__, idx, task_pos[idx]);
                return;
            }
        }
        n_task = params.multiple_choice_tasks;
    }

    // This is needed as usual for LLaMA models
    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));

    printf("%s: preparing task data", __func__);
    fflush(stdout);
    if (n_task > 500) {
        printf("...");
        fflush(stdout);
        std::atomic<int> counter(0);
        std::atomic<int> n_bad(0);
        auto prepare = [&counter, &n_bad, &tasks, ctx, add_bos] () {
            int num_tasks = tasks.size();
            int n_bad_local = 0;
            while (true) {
                int first = counter.fetch_add(K_TOKEN_CHUNK);
                if (first >= num_tasks) {
                    if (n_bad_local > 0) n_bad += n_bad_local;
                    break;
                }
                int last = std::min(first + K_TOKEN_CHUNK, num_tasks);
                for (int i = first; i < last; ++i) {
                    if (!multiple_choice_prepare_one_task(ctx, add_bos, tasks[i], false)) ++n_bad_local;
                }
            }
        };
        size_t max_thread = std::thread::hardware_concurrency();
        max_thread = std::min(max_thread, (tasks.size() + K_TOKEN_CHUNK - 1)/K_TOKEN_CHUNK);
        std::vector<std::thread> workers(max_thread-1);
        for (auto& w : workers) w = std::thread(prepare);
        prepare();
        for (auto& w : workers) w.join();
        printf("done\n");
        fflush(stdout);
        int nbad = n_bad;
        if (nbad > 0) {
            printf("%s: found %d malformed tasks\n", __func__, nbad);
            return;
        }
    } else {
        int n_dot = n_task/100;
        int i_task = 0;
        for (auto& task : tasks) {
            ++i_task;
            if (!multiple_choice_prepare_one_task(ctx, add_bos, task, true)) {
                return;
            }
            if (i_task%n_dot == 0) {
                printf(".");
                fflush(stdout);
            }
        }
        printf("done\n");
    }

    printf("%s : calculating TruthfulQA score over %zu tasks.\n", __func__, tasks.size());

    printf("\ntask\tacc_norm\n");

    const int n_vocab = llama_n_vocab(llama_get_model(ctx));
    const int n_ctx   = llama_n_ctx(ctx);
    const int n_batch = params.n_batch;

    const int max_tasks_per_batch = 32;
    const int max_seq = 4*max_tasks_per_batch;

    llama_batch batch = llama_batch_init(n_ctx, 0, max_seq);

    std::vector<float> tok_logits(n_vocab);
    std::vector<float> batch_logits(n_vocab*n_ctx);

    std::vector<std::pair<size_t, llama_token>> eval_pairs;
    std::vector<float> eval_results;
    std::vector<std::thread> workers(std::thread::hardware_concurrency());
    std::vector<int> batch_indeces;

    int n_done = 0;
    int n_correct = 0;
    int n_tot_answers = 0;

    for (size_t i0 = 0; i0 < tasks.size(); i0++) {
        int n_cur = 0;

        size_t i1 = i0;
        size_t i_batch = 0; // this tells us where in `llama_batch` we are currently

        llama_batch_clear(batch);

        // batch as much tasks as possible into the available context
        // each task has 4 unique seuqnce ids - one for each ending
        // the common prefix is shared among the 4 sequences to save tokens
        // we extract logits only from the last common token and from all ending tokens of each sequence
        int s0 = 0;
        while (n_cur + (int) tasks[i1].required_tokens <= n_ctx) {
            auto& cur_task = tasks[i1];

            int num_answers = cur_task.seq_tokens.size();
            if (s0 + num_answers > max_seq) {
                break;
            }

            if (int(batch_indeces.size()) != num_answers) {
                batch_indeces.resize(num_answers);
            }
            for (int s = 0; s < num_answers; ++s) batch_indeces[s] = s0 + s;

            for (size_t i = 0; i < cur_task.common_prefix; ++i) {
                //llama_batch_add(batch, cur_task.seq_tokens[0][i], i, { s0 + 0, s0 + 1, s0 + 2, s0 + 3}, false);
                llama_batch_add(batch, cur_task.seq_tokens[0][i], i, batch_indeces, false);
            }
            batch.logits[batch.n_tokens - 1] = true; // we need logits for the last token of the common prefix

            for (int s = 0; s < int(cur_task.seq_tokens.size()); ++s) {
                for (size_t i = cur_task.common_prefix; i < cur_task.seq_tokens[s].size(); ++i) {
                    llama_batch_add(batch, cur_task.seq_tokens[s][i], i, { s0 + s }, true);
                }
            }

            s0 += num_answers;

            cur_task.i_batch = i_batch;
            i_batch += cur_task.required_tokens;

            n_cur += cur_task.required_tokens;
            if (++i1 == tasks.size()) {
                break;
            }
        }

        if (i0 == i1) {
            fprintf(stderr, "%s : task %zu does not fit in the context window\n", __func__, i0);
            return;
        }

        llama_kv_cache_clear(ctx);

        // decode all tasks [i0, i1)
        if (!decode_helper(ctx, batch, batch_logits, n_batch, n_vocab)) {
            fprintf(stderr, "%s: llama_decode() failed\n", __func__);
            return;
        }

        // Compute log-probs in parallel
        // First we collect all tasks
        eval_pairs.clear();
        for (size_t i = i0; i < i1; ++i) {
            auto& cur_task = tasks[i];
            size_t li = cur_task.common_prefix;
            for (int s = 0; s < int(cur_task.seq_tokens.size()); ++s) {
                for (size_t j = cur_task.common_prefix; j < cur_task.seq_tokens[s].size() - 1; j++) {
                    eval_pairs.push_back(std::make_pair(cur_task.i_batch + li++, cur_task.seq_tokens[s][j + 1]));
                }
                ++li;
            }
        }
        // Then we do the actual calculation
        compute_logprobs(batch_logits.data(), n_vocab, workers, eval_pairs, eval_results);

        size_t ir = 0;

        // compute the logprobs for each ending of the decoded tasks
        for (size_t i = i0; i < i1; ++i) {
            auto & cur_task = tasks[i];
            //printf("==== Evaluating <%s> with correct answer ", cur_task.question.c_str());
            //for (int j = 0; j < int(cur_task.mc1.labels.size()); ++j) {
            //    if (cur_task.mc1.labels[j] == 1) {
            //        printf("%d", j+1);
            //    }
            //}
            //printf("\n    common_prefix: %zu\n", cur_task.common_prefix);

            std::memcpy(tok_logits.data(), batch_logits.data() + n_vocab*(cur_task.i_batch + cur_task.common_prefix - 1), n_vocab*sizeof(float));

            const auto first_probs = softmax(tok_logits);

            cur_task.log_probs.resize(cur_task.seq_tokens.size());
            for (int s = 0; s < int(cur_task.seq_tokens.size()); ++s) {
                size_t count = 1;
                float  log_prob  = std::log(first_probs[cur_task.seq_tokens[s][cur_task.common_prefix]]);
                for (size_t j = cur_task.common_prefix; j < cur_task.seq_tokens[s].size() - 1; j++) {
                    //printf("        %zu  %g\n", ir, eval_results[ir]);
                    ++count;
                    log_prob += eval_results[ir++];
                }
                cur_task.log_probs[s] = log_prob / count;
                //printf("        Final: %g\n", log_prob / count);
                //printf("    <%s> : %g\n", cur_task.mc1.answers[s].c_str(), log_prob/count);
            }

            // Find the ending with maximum logprob
            size_t logprob_max_idx = 0;
            float  logprob_max_val = cur_task.log_probs[0];
            for (size_t s = 1; s < cur_task.log_probs.size(); s++) {
                if (cur_task.log_probs[s] > logprob_max_val) {
                    logprob_max_val = cur_task.log_probs[s];
                    logprob_max_idx = s;
                }
            }

            n_tot_answers += cur_task.log_probs.size();
            if (cur_task.mc1.labels[logprob_max_idx] == 1) {
                ++n_correct;
            }
            ++n_done;

            // Print the accumulated accuracy mean x 100
            printf("%d\t%.8lf\n", n_done, 100.*n_correct/n_done);
            fflush(stdout);
        }

        i0 = i1 - 1;
    }

    llama_batch_free(batch);

    if (n_done < 100) return;

    float p = 1.f*n_correct/n_done;
    float sigma = sqrt(p*(1-p)/(n_done-1));
    printf("\n Final result: %.4f +/- %.4f\n", 100.f*p, 100.f*sigma);
    p = 1.f*n_done/n_tot_answers;
    sigma = sqrt(p*(1-p)/(n_done-1));
    printf("Random chance: %.4f +/- %.4f\n", 100.f*p, 100.f*sigma);

    printf("\n");
}

static void kl_divergence(llama_context * ctx, const gpt_params & params) {
    if (params.logits_file.empty()) {
        fprintf(stderr, "%s: you must provide a name of a file containing the log probabilities of the base model\n", __func__);
        return;
    }
    std::ifstream in(params.logits_file.c_str(), std::ios::binary);
    if (!in) {
        fprintf(stderr, "%s: failed to open %s\n", __func__, params.logits_file.c_str());
        return;
    }
    {
        char check[9]; check[8] = 0;
        in.read(check, 8);
        if (in.fail() || strncmp("_logits_", check, 8) != 0) {
            fprintf(stderr, "%s: %s does not look like a file containing log-probabilities\n", __func__, params.logits_file.c_str());
            return;
        }
    }

    uint32_t n_ctx;
    in.read((char *)&n_ctx, sizeof(n_ctx));
    if (n_ctx > llama_n_ctx(ctx)) {
        fprintf(stderr, "%s: %s has been computed with %d, while the current context is %d. Increase it with -c and retry\n",
                __func__, params.logits_file.c_str(), n_ctx, params.n_ctx);
    }

    int n_vocab, n_chunk;
    in.read((char *)&n_vocab, sizeof(n_vocab));
    in.read((char *)&n_chunk, sizeof(n_chunk));
    if (in.fail()) {
        fprintf(stderr, "%s: failed reading n_vocab, n_chunk from %s\n", __func__, params.logits_file.c_str());
        return;
    }
    if (n_vocab != llama_n_vocab(llama_get_model(ctx))) {
        fprintf(stderr, "%s: inconsistent vocabulary (%d vs %d)\n", __func__, n_vocab, llama_n_vocab(llama_get_model(ctx)));
    }

    std::vector<llama_token> tokens(n_ctx * n_chunk);
    if (in.read((char *)tokens.data(), tokens.size()*sizeof(tokens[0])).fail()) {
        fprintf(stderr, "%s: failed reading evaluation tokens from %s\n", __func__, params.logits_file.c_str());
        return;
    }

    const int n_batch = params.n_batch;
    const int num_batches = (n_ctx + n_batch - 1)/n_batch;
    const int nv = 2*((n_vocab + 1)/2) + 4;
    const bool add_bos = llama_should_add_bos_token(llama_get_model(ctx));

    std::vector<uint16_t> log_probs_uint16(size_t(n_ctx - 1 - n_ctx/2) * nv);
    std::vector<float> kld_values(size_t(n_ctx - 1 - n_ctx/2)*n_chunk);
    std::vector<float> logits;
    if (num_batches > 1) {
        logits.reserve(n_ctx * n_vocab);
    }

    std::vector<std::thread> workers(std::thread::hardware_concurrency() - 1);

    auto mean_and_uncertainty = [] (double sum, double sum2, size_t count) {
        if (count < 1) {
            return std::make_pair(0., 0.);
        }
        double f = sum/count;
        double df = sum2/count - f*f;
        df = df > 0 && count > 10 ? sqrt(df/(count-1)) : 0.;
        return std::make_pair(f, df);
    };

    kl_divergence_result kld;
    auto kld_ptr = kld_values.data();

    for (int i = 0; i < n_chunk; ++i) {
        const int start =     i * n_ctx;
        const int end   = start + n_ctx;

        const auto t_start = std::chrono::high_resolution_clock::now();

        if (in.read((char *)log_probs_uint16.data(), log_probs_uint16.size()*sizeof(uint16_t)).fail()) {
            fprintf(stderr, "%s: failed reading log-probs for chunk %d\n", __func__, i);
            return;
        }

        // clear the KV cache
        llama_kv_cache_clear(ctx);

        for (int j = 0; j < num_batches; ++j) {
            const int batch_start = start + j * n_batch;
            const int batch_size  = std::min(end - batch_start, n_batch);

            // save original token and restore it after eval
            const auto token_org = tokens[batch_start];

            // add BOS token for the first batch of each chunk
            if (add_bos && j == 0) {
                tokens[batch_start] = llama_token_bos(llama_get_model(ctx));
            }

            if (llama_decode(ctx, llama_batch_get_one(tokens.data() + batch_start, batch_size, j * n_batch, 0))) {
                fprintf(stderr, "%s : failed to eval\n", __func__);
                return;
            }

            // restore the original token in case it was set to BOS
            tokens[batch_start] = token_org;

            if (num_batches > 1) {
                const auto * batch_logits = llama_get_logits(ctx);
                logits.insert(logits.end(), batch_logits, batch_logits + batch_size * n_vocab);
            }
        }

        const auto t_end = std::chrono::high_resolution_clock::now();

        if (i == 0) {
            const float t_total = std::chrono::duration<float>(t_end - t_start).count();
            fprintf(stderr, "%s: %.2f seconds per pass - ETA ", __func__, t_total);
            int total_seconds = (int)(t_total * n_chunk);
            if (total_seconds >= 60*60) {
                fprintf(stderr, "%d hours ", total_seconds / (60*60));
                total_seconds = total_seconds % (60*60);
            }
            fprintf(stderr, "%.2f minutes\n", total_seconds / 60.0);

            printf("\nchunk        PPL          ln(PPL(Q)/PPL(base))          KL-Divergence           Same top\n");
        }

        const int first = n_ctx/2;
        const float * all_logits = num_batches > 1 ? logits.data() : llama_get_logits(ctx);
        process_logits(n_vocab, all_logits + first*n_vocab, tokens.data() + start + first, n_ctx - 1 - first,
                workers, log_probs_uint16, kld, kld_ptr);
        kld_ptr += n_ctx - 1 - first;

        auto ppl           = mean_and_uncertainty(kld.sum_nll, kld.sum_nll2, kld.count);
        auto log_ppl_ratio = mean_and_uncertainty(kld.sum_nll_diff, kld.sum_nll_diff2, kld.count);
        auto kl_div        = mean_and_uncertainty(kld.sum_kld, kld.sum_kld2, kld.count);
        auto p_top = 1.*kld.n_same_top/kld.count;
        auto d_p_top = sqrt(p_top*(1 - p_top)/(kld.count - 1));

        printf("%4d    %10.4lf    %10.5lf ± %10.5f    %10.5f ± %10.5lf    %.5f ± %.5f\n", i+1, exp(ppl.first),
                log_ppl_ratio.first, log_ppl_ratio.second, kl_div.first, kl_div.second,
                p_top, d_p_top);

        fflush(stdout);

        logits.clear();
    }
    printf("\n");

    if (kld.count < 100) return; // we do not wish to do statistics on so few values

    std::sort(kld_values.begin(), kld_values.end());

    printf("===== KL-divergence statistics\n");
    auto kl_div = mean_and_uncertainty(kld.sum_kld, kld.sum_kld2, kld.count);
    printf("Average: %10.6f ±%10.6lf\n", kl_div.first, kl_div.second);
    auto kld_median = kld_values.size()%2 == 0 ? 0.5f*(kld_values[kld_values.size()/2] + kld_values[kld_values.size()/2-1])
                                               : kld_values[kld_values.size()/2];
    printf("Median : %10.6f\n", kld_median);

    auto percentile = [&kld_values] (float fraction) {
        if (fraction <= 0) return kld_values.front();
        if (fraction >= 1) return kld_values.back();
        float p = fraction*(kld_values.size() - 1);
        size_t ip = size_t(p); p -= ip;
        return (1 - p)*kld_values[ip] + p*kld_values[std::min(ip+1, kld_values.size()-1)];
    };

    printf("Maximum: %10.6f\n", kld_values.back());
    printf("KLD_99 : %10.6f\n", percentile(0.99f));
    printf("KLD_95 : %10.6f\n", percentile(0.95f));
    printf("KLD_90 : %10.6f\n", percentile(0.90f));

    printf("Minimum: %10.6f\n", kld_values.front());
    printf("KLD_01 : %10.6f\n", percentile(0.01f));
    printf("KLD_05 : %10.6f\n", percentile(0.05f));
    printf("KLD_10 : %10.6f\n", percentile(0.10f));

}

int main(int argc, char ** argv) {
    gpt_params params;

    params.n_batch = 512;
    if (!gpt_params_parse(argc, argv, params)) {
        return 1;
    }

    params.logits_all = true;
    params.n_batch = std::min(params.n_batch, params.n_ctx);

    if (params.ppl_stride > 0) {
        fprintf(stderr, "Will perform strided perplexity calculation -> adjusting context size from %d to %d\n",
                params.n_ctx, params.n_ctx + params.ppl_stride/2);
        params.n_ctx += params.ppl_stride/2;
    }

    print_build_info();

    if (params.seed == LLAMA_DEFAULT_SEED) {
        params.seed = time(NULL);
    }

    fprintf(stderr, "%s: seed  = %u\n", __func__, params.seed);

    std::mt19937 rng(params.seed);
    if (params.random_prompt) {
        params.prompt = gpt_random_prompt(rng);
    }

    llama_backend_init(params.numa);

    llama_model * model;
    llama_context * ctx;

    // load the model and apply lora adapter, if any
    std::tie(model, ctx) = llama_init_from_gpt_params(params);
    if (model == NULL) {
        fprintf(stderr, "%s: error: unable to load model\n", __func__);
        return 1;
    }

    const int n_ctx_train = llama_n_ctx_train(model);
    if (params.n_ctx > n_ctx_train) {
        fprintf(stderr, "%s: warning: model was trained on only %d context tokens (%d specified)\n",
                __func__, n_ctx_train, params.n_ctx);
    }

    // print system information
    {
        fprintf(stderr, "\n");
        fprintf(stderr, "%s\n", get_system_info(params).c_str());
    }

    struct results_perplexity results;
    if (params.hellaswag) {
        hellaswag_score(ctx, params);
    } else if (params.winogrande) {
        winogrande_score(ctx, params);
    } else if (params.multiple_choice) {
        multiple_choice_score(ctx, params);
    } else if (params.kl_divergence) {
        kl_divergence(ctx, params);
    } else {
        results = perplexity(ctx, params);
    }

    llama_print_timings(ctx);
    write_logfile(ctx, params, model, results);

    llama_free(ctx);
    llama_free_model(model);

    llama_backend_free();

    return 0;
}