text: /*
   * Copyright (c) 2018-2020, Facebook, Inc.
   * All rights reserved.
   *
   * This source code is licensed under both the BSD-style license (found in the
   * LICENSE file in the root directory of this source tree) and the GPLv2 (found
   * in the COPYING file in the root directory of this source tree).
   * You may select, at your option, one of the above-listed licenses.
   */
  
  /*-*************************************
  *  Dependencies
  ***************************************/
  #include <stdio.h>  /* fprintf */
  #include <stdlib.h> /* malloc, free, qsort */
  #include <string.h> /* memset */
  #include <time.h>   /* clock */
  
  #include "../common/mem.h" /* read */
  #include "../common/pool.h"
  #include "../common/threading.h"
  #include "cover.h"
  #include "../common/zstd_internal.h" /* includes zstd.h */
  #ifndef ZDICT_STATIC_LINKING_ONLY
  #define ZDICT_STATIC_LINKING_ONLY
  #endif
  #include "zdict.h"
  
  
  /*-*************************************
  *  Constants
  ***************************************/
  #define FASTCOVER_MAX_SAMPLES_SIZE (sizeof(size_t) == 8 ? ((unsigned)-1) : ((unsigned)1 GB))
  #define FASTCOVER_MAX_F 31
  #define FASTCOVER_MAX_ACCEL 10
  #define DEFAULT_SPLITPOINT 0.75
  #define DEFAULT_F 20
  #define DEFAULT_ACCEL 1
  
  
  /*-*************************************
  *  Console display
  ***************************************/
  static int g_displayLevel = 2;
  #define DISPLAY(...)                                                           \
    {                                                                            \
      fprintf(stderr, __VA_ARGS__);                                              \
      fflush(stderr);                                                            \
    }
  #define LOCALDISPLAYLEVEL(displayLevel, l, ...)                                \
    if (displayLevel >= l) {                                                     \
      DISPLAY(__VA_ARGS__);                                                      \
    } /* 0 : no display;   1: errors;   2: default;  3: details;  4: debug */
  #define DISPLAYLEVEL(l, ...) LOCALDISPLAYLEVEL(g_displayLevel, l, __VA_ARGS__)
  
  #define LOCALDISPLAYUPDATE(displayLevel, l, ...)                               \
    if (displayLevel >= l) {                                                     \
      if ((clock() - g_time > refreshRate) || (displayLevel >= 4)) {             \
        g_time = clock();                                                        \
        DISPLAY(__VA_ARGS__);                                                    \
      }                                                                          \
    }
  #define DISPLAYUPDATE(l, ...) LOCALDISPLAYUPDATE(g_displayLevel, l, __VA_ARGS__)
  static const clock_t refreshRate = CLOCKS_PER_SEC * 15 / 100;
  static clock_t g_time = 0;
  
  
  /*-*************************************
  * Hash Functions
  ***************************************/
  static const U64 prime6bytes = 227718039650203ULL;
  static size_t ZSTD_hash6(U64 u, U32 h) { return (size_t)(((u  << (64-48)) * prime6bytes) >> (64-h)) ; }
  static size_t ZSTD_hash6Ptr(const void* p, U32 h) { return ZSTD_hash6(MEM_readLE64(p), h); }
  
  static const U64 prime8bytes = 0xCF1BBCDCB7A56463ULL;
  static size_t ZSTD_hash8(U64 u, U32 h) { return (size_t)(((u) * prime8bytes) >> (64-h)) ; }
  static size_t ZSTD_hash8Ptr(const void* p, U32 h) { return ZSTD_hash8(MEM_readLE64(p), h); }
  
  
  /**
   * Hash the d-byte value pointed to by p and mod 2^f
   */
  static size_t FASTCOVER_hashPtrToIndex(const void* p, U32 h, unsigned d) {
    if (d == 6) {
      return ZSTD_hash6Ptr(p, h) & ((1 << h) - 1);
    }
    return ZSTD_hash8Ptr(p, h) & ((1 << h) - 1);
  }
  
  
  /*-*************************************
  * Acceleration
  ***************************************/
  typedef struct {
    unsigned finalize;    /* Percentage of training samples used for ZDICT_finalizeDictionary */
    unsigned skip;        /* Number of dmer skipped between each dmer counted in computeFrequency */
  } FASTCOVER_accel_t;
  
  
  static const FASTCOVER_accel_t FASTCOVER_defaultAccelParameters[FASTCOVER_MAX_ACCEL+1] = {
    { 100, 0 },   /* accel = 0, should not happen because accel = 0 defaults to accel = 1 */
    { 100, 0 },   /* accel = 1 */
    { 50, 1 },   /* accel = 2 */
    { 34, 2 },   /* accel = 3 */
    { 25, 3 },   /* accel = 4 */
    { 20, 4 },   /* accel = 5 */
    { 17, 5 },   /* accel = 6 */
    { 14, 6 },   /* accel = 7 */
    { 13, 7 },   /* accel = 8 */
    { 11, 8 },   /* accel = 9 */
    { 10, 9 },   /* accel = 10 */
  };
  
  
  /*-*************************************
  * Context
  ***************************************/
  typedef struct {
    const BYTE *samples;
    size_t *offsets;
    const size_t *samplesSizes;
    size_t nbSamples;
    size_t nbTrainSamples;
    size_t nbTestSamples;
    size_t nbDmers;
    U32 *freqs;
    unsigned d;
    unsigned f;
    FASTCOVER_accel_t accelParams;
  } FASTCOVER_ctx_t;
  
  
  /*-*************************************
  *  Helper functions
  ***************************************/
  /**
   * Selects the best segment in an epoch.
   * Segments of are scored according to the function:
   *
   * Let F(d) be the frequency of all dmers with hash value d.
   * Let S_i be hash value of the dmer at position i of segment S which has length k.
   *
   *     Score(S) = F(S_1) + F(S_2) + ... + F(S_{k-d+1})
   *
   * Once the dmer with hash value d is in the dictionary we set F(d) = 0.
   */
  static COVER_segment_t FASTCOVER_selectSegment(const FASTCOVER_ctx_t *ctx,
                                                U32 *freqs, U32 begin, U32 end,
                                                ZDICT_cover_params_t parameters,
                                                U16* segmentFreqs) {
    /* Constants */
    const U32 k = parameters.k;
    const U32 d = parameters.d;
    const U32 f = ctx->f;
    const U32 dmersInK = k - d + 1;
  
    /* Try each segment (activeSegment) and save the best (bestSegment) */
    COVER_segment_t bestSegment = {0, 0, 0};
    COVER_segment_t activeSegment;
  
    /* Reset the activeDmers in the segment */
    /* The activeSegment starts at the beginning of the epoch. */
    activeSegment.begin = begin;
    activeSegment.end = begin;
    activeSegment.score = 0;
  
    /* Slide the activeSegment through the whole epoch.
     * Save the best segment in bestSegment.
     */
    while (activeSegment.end < end) {
      /* Get hash value of current dmer */
      const size_t idx = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.end, f, d);
  
      /* Add frequency of this index to score if this is the first occurrence of index in active segment */
      if (segmentFreqs[idx] == 0) {
        activeSegment.score += freqs[idx];
      }
      /* Increment end of segment and segmentFreqs*/
      activeSegment.end += 1;
      segmentFreqs[idx] += 1;
      /* If the window is now too large, drop the first position */
      if (activeSegment.end - activeSegment.begin == dmersInK + 1) {
        /* Get hash value of the dmer to be eliminated from active segment */
        const size_t delIndex = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.begin, f, d);
        segmentFreqs[delIndex] -= 1;
        /* Subtract frequency of this index from score if this is the last occurrence of this index in active segment */
        if (segmentFreqs[delIndex] == 0) {
          activeSegment.score -= freqs[delIndex];
        }
        /* Increment start of segment */
        activeSegment.begin += 1;
      }
  
      /* If this segment is the best so far save it */
      if (activeSegment.score > bestSegment.score) {
        bestSegment = activeSegment;
      }
    }
  
    /* Zero out rest of segmentFreqs array */
    while (activeSegment.begin < end) {
      const size_t delIndex = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.begin, f, d);
      segmentFreqs[delIndex] -= 1;
      activeSegment.begin += 1;
    }
  
    {
      /*  Zero the frequency of hash value of each dmer covered by the chosen segment. */
      U32 pos;
      for (pos = bestSegment.begin; pos != bestSegment.end; ++pos) {
        const size_t i = FASTCOVER_hashPtrToIndex(ctx->samples + pos, f, d);
        freqs[i] = 0;
      }
    }
  
    return bestSegment;
  }
  
  
  static int FASTCOVER_checkParameters(ZDICT_cover_params_t parameters,
                                       size_t maxDictSize, unsigned f,
                                       unsigned accel) {
    /* k, d, and f are required parameters */
    if (parameters.d == 0 || parameters.k == 0) {
      DISPLAYLEVEL(1, "d or k is 0\n");
      return 0;
    }
    /* d has to be 6 or 8 */
    if (parameters.d != 6 && parameters.d != 8) {
      DISPLAYLEVEL(1, "d is not 6 or 8\n");
      return 0;
    }
    /* k <= maxDictSize */
    if (parameters.k > maxDictSize) {
      DISPLAYLEVEL(1, "k > maxDictSize\n");
      return 0;
    }
    /* d <= k */
    if (parameters.d > parameters.k) {
      DISPLAYLEVEL(1, "d > k\n");
      return 0;
    }
    /* 0 < f <= FASTCOVER_MAX_F*/
    if (f > FASTCOVER_MAX_F || f == 0) {
      DISPLAYLEVEL(1, "f not in range\n");
      return 0;
    }
    /* 0 < splitPoint <= 1 */
    if (parameters.splitPoint <= 0 || parameters.splitPoint > 1) {
      DISPLAYLEVEL(1, "splitPoint not in range\n");
      return 0;
    }
    /* 0 < accel <= 10 */
    if (accel > 10 || accel == 0) {
      DISPLAYLEVEL(1, "accel not in range\n");
      return 0;
    }
    return 1;
  }
  
  
  /**
   * Clean up a context initialized with `FASTCOVER_ctx_init()`.
   */
  static void
  FASTCOVER_ctx_destroy(FASTCOVER_ctx_t* ctx)
  {
      if (!ctx) return;
  
      free(ctx->freqs);
      ctx->freqs = NULL;
  
      free(ctx->offsets);
      ctx->offsets = NULL;
  }
  
  
  /**
   * Calculate for frequency of hash value of each dmer in ctx->samples
   */
  static void
  FASTCOVER_computeFrequency(U32* freqs, const FASTCOVER_ctx_t* ctx)
  {
      const unsigned f = ctx->f;
      const unsigned d = ctx->d;
      const unsigned skip = ctx->accelParams.skip;
      const unsigned readLength = MAX(d, 8);
      size_t i;
      assert(ctx->nbTrainSamples >= 5);
      assert(ctx->nbTrainSamples <= ctx->nbSamples);
      for (i = 0; i < ctx->nbTrainSamples; i++) {
          size_t start = ctx->offsets[i];  /* start of current dmer */
          size_t const currSampleEnd = ctx->offsets[i+1];
          while (start + readLength <= currSampleEnd) {
              const size_t dmerIndex = FASTCOVER_hashPtrToIndex(ctx->samples + start, f, d);
              freqs[dmerIndex]++;
              start = start + skip + 1;
          }
      }
  }
  
  
  /**
   * Prepare a context for dictionary building.
   * The context is only dependent on the parameter `d` and can used multiple
   * times.
   * Returns 0 on success or error code on error.
   * The context must be destroyed with `FASTCOVER_ctx_destroy()`.
   */
  static size_t
  FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx,
                     const void* samplesBuffer,
                     const size_t* samplesSizes, unsigned nbSamples,
                     unsigned d, double splitPoint, unsigned f,
                     FASTCOVER_accel_t accelParams)
  {
      const BYTE* const samples = (const BYTE*)samplesBuffer;
      const size_t totalSamplesSize = COVER_sum(samplesSizes, nbSamples);
      /* Split samples into testing and training sets */
      const unsigned nbTrainSamples = splitPoint < 1.0 ? (unsigned)((double)nbSamples * splitPoint) : nbSamples;
      const unsigned nbTestSamples = splitPoint < 1.0 ? nbSamples - nbTrainSamples : nbSamples;
      const size_t trainingSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes, nbTrainSamples) : totalSamplesSize;
      const size_t testSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes + nbTrainSamples, nbTestSamples) : totalSamplesSize;
  
      /* Checks */
      if (totalSamplesSize < MAX(d, sizeof(U64)) ||
          totalSamplesSize >= (size_t)FASTCOVER_MAX_SAMPLES_SIZE) {
          DISPLAYLEVEL(1, "Total samples size is too large (%u MB), maximum size is %u MB\n",
                      (unsigned)(totalSamplesSize >> 20), (FASTCOVER_MAX_SAMPLES_SIZE >> 20));
          return ERROR(srcSize_wrong);
      }
  
      /* Check if there are at least 5 training samples */
      if (nbTrainSamples < 5) {
          DISPLAYLEVEL(1, "Total number of training samples is %u and is invalid\n", nbTrainSamples);
          return ERROR(srcSize_wrong);
      }
  
      /* Check if there's testing sample */
      if (nbTestSamples < 1) {
          DISPLAYLEVEL(1, "Total number of testing samples is %u and is invalid.\n", nbTestSamples);
          return ERROR(srcSize_wrong);
      }
  
      /* Zero the context */
      memset(ctx, 0, sizeof(*ctx));
      DISPLAYLEVEL(2, "Training on %u samples of total size %u\n", nbTrainSamples,
                      (unsigned)trainingSamplesSize);
      DISPLAYLEVEL(2, "Testing on %u samples of total size %u\n", nbTestSamples,
                      (unsigned)testSamplesSize);
  
      ctx->samples = samples;
      ctx->samplesSizes = samplesSizes;
      ctx->nbSamples = nbSamples;
      ctx->nbTrainSamples = nbTrainSamples;
      ctx->nbTestSamples = nbTestSamples;
      ctx->nbDmers = trainingSamplesSize - MAX(d, sizeof(U64)) + 1;
      ctx->d = d;
      ctx->f = f;
      ctx->accelParams = accelParams;
  
      /* The offsets of each file */
      ctx->offsets = (size_t*)calloc((nbSamples + 1), sizeof(size_t));
      if (ctx->offsets == NULL) {
          DISPLAYLEVEL(1, "Failed to allocate scratch buffers \n");
          FASTCOVER_ctx_destroy(ctx);
          return ERROR(memory_allocation);
      }
  
      /* Fill offsets from the samplesSizes */
      {   U32 i;
          ctx->offsets[0] = 0;
          assert(nbSamples >= 5);
          for (i = 1; i <= nbSamples; ++i) {
              ctx->offsets[i] = ctx->offsets[i - 1] + samplesSizes[i - 1];
          }
      }
  
      /* Initialize frequency array of size 2^f */
      ctx->freqs = (U32*)calloc(((U64)1 << f), sizeof(U32));
      if (ctx->freqs == NULL) {
          DISPLAYLEVEL(1, "Failed to allocate frequency table \n");
          FASTCOVER_ctx_destroy(ctx);
          return ERROR(memory_allocation);
      }
  
      DISPLAYLEVEL(2, "Computing frequencies\n");
      FASTCOVER_computeFrequency(ctx->freqs, ctx);
  
      return 0;
  }
  
  
  /**
   * Given the prepared context build the dictionary.
   */
  static size_t
  FASTCOVER_buildDictionary(const FASTCOVER_ctx_t* ctx,
                            U32* freqs,
                            void* dictBuffer, size_t dictBufferCapacity,
                            ZDICT_cover_params_t parameters,
                            U16* segmentFreqs)
  {
    BYTE *const dict = (BYTE *)dictBuffer;
    size_t tail = dictBufferCapacity;
    /* Divide the data into epochs. We will select one segment from each epoch. */
    const COVER_epoch_info_t epochs = COVER_computeEpochs(
        (U32)dictBufferCapacity, (U32)ctx->nbDmers, parameters.k, 1);
    const size_t maxZeroScoreRun = 10;
    size_t zeroScoreRun = 0;
    size_t epoch;
    DISPLAYLEVEL(2, "Breaking content into %u epochs of size %u\n",
                  (U32)epochs.num, (U32)epochs.size);
    /* Loop through the epochs until there are no more segments or the dictionary
     * is full.
     */
    for (epoch = 0; tail > 0; epoch = (epoch + 1) % epochs.num) {
      const U32 epochBegin = (U32)(epoch * epochs.size);
      const U32 epochEnd = epochBegin + epochs.size;
      size_t segmentSize;
      /* Select a segment */
      COVER_segment_t segment = FASTCOVER_selectSegment(
          ctx, freqs, epochBegin, epochEnd, parameters, segmentFreqs);
  
      /* If the segment covers no dmers, then we are out of content.
       * There may be new content in other epochs, for continue for some time.
       */
      if (segment.score == 0) {
        if (++zeroScoreRun >= maxZeroScoreRun) {
            break;
        }
        continue;
      }
      zeroScoreRun = 0;
  
      /* Trim the segment if necessary and if it is too small then we are done */
      segmentSize = MIN(segment.end - segment.begin + parameters.d - 1, tail);
      if (segmentSize < parameters.d) {
        break;
      }
  
      /* We fill the dictionary from the back to allow the best segments to be
       * referenced with the smallest offsets.
       */
      tail -= segmentSize;
      memcpy(dict + tail, ctx->samples + segment.begin, segmentSize);
      DISPLAYUPDATE(
          2, "\r%u%%       ",
          (unsigned)(((dictBufferCapacity - tail) * 100) / dictBufferCapacity));
    }
    DISPLAYLEVEL(2, "\r%79s\r", "");
    return tail;
  }
  
  /**
   * Parameters for FASTCOVER_tryParameters().
   */
  typedef struct FASTCOVER_tryParameters_data_s {
      const FASTCOVER_ctx_t* ctx;
      COVER_best_t* best;
      size_t dictBufferCapacity;
      ZDICT_cover_params_t parameters;
  } FASTCOVER_tryParameters_data_t;
  
  
  /**
   * Tries a set of parameters and updates the COVER_best_t with the results.
   * This function is thread safe if zstd is compiled with multithreaded support.
   * It takes its parameters as an *OWNING* opaque pointer to support threading.
   */
  static void FASTCOVER_tryParameters(void *opaque)
  {
    /* Save parameters as local variables */
    FASTCOVER_tryParameters_data_t *const data = (FASTCOVER_tryParameters_data_t *)opaque;
    const FASTCOVER_ctx_t *const ctx = data->ctx;
    const ZDICT_cover_params_t parameters = data->parameters;
    size_t dictBufferCapacity = data->dictBufferCapacity;
    size_t totalCompressedSize = ERROR(GENERIC);
    /* Initialize array to keep track of frequency of dmer within activeSegment */
    U16* segmentFreqs = (U16 *)calloc(((U64)1 << ctx->f), sizeof(U16));
    /* Allocate space for hash table, dict, and freqs */
    BYTE *const dict = (BYTE * const)malloc(dictBufferCapacity);
    COVER_dictSelection_t selection = COVER_dictSelectionError(ERROR(GENERIC));
    U32 *freqs = (U32*) malloc(((U64)1 << ctx->f) * sizeof(U32));
    if (!segmentFreqs || !dict || !freqs) {
      DISPLAYLEVEL(1, "Failed to allocate buffers: out of memory\n");
      goto _cleanup;
    }
    /* Copy the frequencies because we need to modify them */
    memcpy(freqs, ctx->freqs, ((U64)1 << ctx->f) * sizeof(U32));
    /* Build the dictionary */
    { const size_t tail = FASTCOVER_buildDictionary(ctx, freqs, dict, dictBufferCapacity,
                                                      parameters, segmentFreqs);
  
      const unsigned nbFinalizeSamples = (unsigned)(ctx->nbTrainSamples * ctx->accelParams.finalize / 100);
      selection = COVER_selectDict(dict + tail, dictBufferCapacity - tail,
           ctx->samples, ctx->samplesSizes, nbFinalizeSamples, ctx->nbTrainSamples, ctx->nbSamples, parameters, ctx->offsets,
           totalCompressedSize);
  
      if (COVER_dictSelectionIsError(selection)) {
        DISPLAYLEVEL(1, "Failed to select dictionary\n");
        goto _cleanup;
      }
    }
  _cleanup:
    free(dict);
    COVER_best_finish(data->best, parameters, selection);
    free(data);
    free(segmentFreqs);
    COVER_dictSelectionFree(selection);
    free(freqs);
  }
  
  
  static void
  FASTCOVER_convertToCoverParams(ZDICT_fastCover_params_t fastCoverParams,
                                 ZDICT_cover_params_t* coverParams)
  {
      coverParams->k = fastCoverParams.k;
      coverParams->d = fastCoverParams.d;
      coverParams->steps = fastCoverParams.steps;
      coverParams->nbThreads = fastCoverParams.nbThreads;
      coverParams->splitPoint = fastCoverParams.splitPoint;
      coverParams->zParams = fastCoverParams.zParams;
      coverParams->shrinkDict = fastCoverParams.shrinkDict;
  }
  
  
  static void
  FASTCOVER_convertToFastCoverParams(ZDICT_cover_params_t coverParams,
                                     ZDICT_fastCover_params_t* fastCoverParams,
                                     unsigned f, unsigned accel)
  {
      fastCoverParams->k = coverParams.k;
      fastCoverParams->d = coverParams.d;
      fastCoverParams->steps = coverParams.steps;
      fastCoverParams->nbThreads = coverParams.nbThreads;
      fastCoverParams->splitPoint = coverParams.splitPoint;
      fastCoverParams->f = f;
      fastCoverParams->accel = accel;
      fastCoverParams->zParams = coverParams.zParams;
      fastCoverParams->shrinkDict = coverParams.shrinkDict;
  }
  
  
  ZDICTLIB_API size_t
  ZDICT_trainFromBuffer_fastCover(void* dictBuffer, size_t dictBufferCapacity,
                                  const void* samplesBuffer,
                                  const size_t* samplesSizes, unsigned nbSamples,
                                  ZDICT_fastCover_params_t parameters)
  {
      BYTE* const dict = (BYTE*)dictBuffer;
      FASTCOVER_ctx_t ctx;
      ZDICT_cover_params_t coverParams;
      FASTCOVER_accel_t accelParams;
      /* Initialize global data */
      g_displayLevel = parameters.zParams.notificationLevel;
      /* Assign splitPoint and f if not provided */
      parameters.splitPoint = 1.0;
      parameters.f = parameters.f == 0 ? DEFAULT_F : parameters.f;
      parameters.accel = parameters.accel == 0 ? DEFAULT_ACCEL : parameters.accel;
      /* Convert to cover parameter */
      memset(&coverParams, 0 , sizeof(coverParams));
      FASTCOVER_convertToCoverParams(parameters, &coverParams);
      /* Checks */
      if (!FASTCOVER_checkParameters(coverParams, dictBufferCapacity, parameters.f,
                                     parameters.accel)) {
        DISPLAYLEVEL(1, "FASTCOVER parameters incorrect\n");
        return ERROR(parameter_outOfBound);
      }
      if (nbSamples == 0) {
        DISPLAYLEVEL(1, "FASTCOVER must have at least one input file\n");
        return ERROR(srcSize_wrong);
      }
      if (dictBufferCapacity < ZDICT_DICTSIZE_MIN) {
        DISPLAYLEVEL(1, "dictBufferCapacity must be at least %u\n",
                     ZDICT_DICTSIZE_MIN);
        return ERROR(dstSize_tooSmall);
      }
      /* Assign corresponding FASTCOVER_accel_t to accelParams*/
      accelParams = FASTCOVER_defaultAccelParameters[parameters.accel];
      /* Initialize context */
      {
        size_t const initVal = FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples,
                              coverParams.d, parameters.splitPoint, parameters.f,
                              accelParams);
        if (ZSTD_isError(initVal)) {
          DISPLAYLEVEL(1, "Failed to initialize context\n");
          return initVal;
        }
      }
      COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, g_displayLevel);
      /* Build the dictionary */
      DISPLAYLEVEL(2, "Building dictionary\n");
      {
        /* Initialize array to keep track of frequency of dmer within activeSegment */
        U16* segmentFreqs = (U16 *)calloc(((U64)1 << parameters.f), sizeof(U16));
        const size_t tail = FASTCOVER_buildDictionary(&ctx, ctx.freqs, dictBuffer,
                                                  dictBufferCapacity, coverParams, segmentFreqs);
        const unsigned nbFinalizeSamples = (unsigned)(ctx.nbTrainSamples * ctx.accelParams.finalize / 100);
        const size_t dictionarySize = ZDICT_finalizeDictionary(
            dict, dictBufferCapacity, dict + tail, dictBufferCapacity - tail,
            samplesBuffer, samplesSizes, nbFinalizeSamples, coverParams.zParams);
        if (!ZSTD_isError(dictionarySize)) {
            DISPLAYLEVEL(2, "Constructed dictionary of size %u\n",
                        (unsigned)dictionarySize);
        }
        FASTCOVER_ctx_destroy(&ctx);
        free(segmentFreqs);
        return dictionarySize;
      }
  }
  
  
  ZDICTLIB_API size_t
  ZDICT_optimizeTrainFromBuffer_fastCover(
                      void* dictBuffer, size_t dictBufferCapacity,
                      const void* samplesBuffer,
                      const size_t* samplesSizes, unsigned nbSamples,
                      ZDICT_fastCover_params_t* parameters)
  {
      ZDICT_cover_params_t coverParams;
      FASTCOVER_accel_t accelParams;
      /* constants */
      const unsigned nbThreads = parameters->nbThreads;
      const double splitPoint =
          parameters->splitPoint <= 0.0 ? DEFAULT_SPLITPOINT : parameters->splitPoint;
      const unsigned kMinD = parameters->d == 0 ? 6 : parameters->d;
      const unsigned kMaxD = parameters->d == 0 ? 8 : parameters->d;
      const unsigned kMinK = parameters->k == 0 ? 50 : parameters->k;
      const unsigned kMaxK = parameters->k == 0 ? 2000 : parameters->k;
      const unsigned kSteps = parameters->steps == 0 ? 40 : parameters->steps;
      const unsigned kStepSize = MAX((kMaxK - kMinK) / kSteps, 1);
      const unsigned kIterations =
          (1 + (kMaxD - kMinD) / 2) * (1 + (kMaxK - kMinK) / kStepSize);
      const unsigned f = parameters->f == 0 ? DEFAULT_F : parameters->f;
      const unsigned accel = parameters->accel == 0 ? DEFAULT_ACCEL : parameters->accel;
      const unsigned shrinkDict = 0;
      /* Local variables */
      const int displayLevel = parameters->zParams.notificationLevel;
      unsigned iteration = 1;
      unsigned d;
      unsigned k;
      COVER_best_t best;
      POOL_ctx *pool = NULL;
      int warned = 0;
      /* Checks */
      if (splitPoint <= 0 || splitPoint > 1) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect splitPoint\n");
        return ERROR(parameter_outOfBound);
      }
      if (accel == 0 || accel > FASTCOVER_MAX_ACCEL) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect accel\n");
        return ERROR(parameter_outOfBound);
      }
      if (kMinK < kMaxD || kMaxK < kMinK) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect k\n");
        return ERROR(parameter_outOfBound);
      }
      if (nbSamples == 0) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "FASTCOVER must have at least one input file\n");
        return ERROR(srcSize_wrong);
      }
      if (dictBufferCapacity < ZDICT_DICTSIZE_MIN) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "dictBufferCapacity must be at least %u\n",
                     ZDICT_DICTSIZE_MIN);
        return ERROR(dstSize_tooSmall);
      }
      if (nbThreads > 1) {
        pool = POOL_create(nbThreads, 1);
        if (!pool) {
          return ERROR(memory_allocation);
        }
      }
      /* Initialization */
      COVER_best_init(&best);
      memset(&coverParams, 0 , sizeof(coverParams));
      FASTCOVER_convertToCoverParams(*parameters, &coverParams);
      accelParams = FASTCOVER_defaultAccelParameters[accel];
      /* Turn down global display level to clean up display at level 2 and below */
      g_displayLevel = displayLevel == 0 ? 0 : displayLevel - 1;
      /* Loop through d first because each new value needs a new context */
      LOCALDISPLAYLEVEL(displayLevel, 2, "Trying %u different sets of parameters\n",
                        kIterations);
      for (d = kMinD; d <= kMaxD; d += 2) {
        /* Initialize the context for this value of d */
        FASTCOVER_ctx_t ctx;
        LOCALDISPLAYLEVEL(displayLevel, 3, "d=%u\n", d);
        {
          size_t const initVal = FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples, d, splitPoint, f, accelParams);
          if (ZSTD_isError(initVal)) {
            LOCALDISPLAYLEVEL(displayLevel, 1, "Failed to initialize context\n");
            COVER_best_destroy(&best);
            POOL_free(pool);
            return initVal;
          }
        }
        if (!warned) {
          COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, displayLevel);
          warned = 1;
        }
        /* Loop through k reusing the same context */
        for (k = kMinK; k <= kMaxK; k += kStepSize) {
          /* Prepare the arguments */
          FASTCOVER_tryParameters_data_t *data = (FASTCOVER_tryParameters_data_t *)malloc(
              sizeof(FASTCOVER_tryParameters_data_t));
          LOCALDISPLAYLEVEL(displayLevel, 3, "k=%u\n", k);
          if (!data) {
            LOCALDISPLAYLEVEL(displayLevel, 1, "Failed to allocate parameters\n");
            COVER_best_destroy(&best);
            FASTCOVER_ctx_destroy(&ctx);
            POOL_free(pool);
            return ERROR(memory_allocation);
          }
          data->ctx = &ctx;
          data->best = &best;
          data->dictBufferCapacity = dictBufferCapacity;
          data->parameters = coverParams;
          data->parameters.k = k;
          data->parameters.d = d;
          data->parameters.splitPoint = splitPoint;
          data->parameters.steps = kSteps;
          data->parameters.shrinkDict = shrinkDict;
          data->parameters.zParams.notificationLevel = g_displayLevel;
          /* Check the parameters */
          if (!FASTCOVER_checkParameters(data->parameters, dictBufferCapacity,
                                         data->ctx->f, accel)) {
            DISPLAYLEVEL(1, "FASTCOVER parameters incorrect\n");
            free(data);
            continue;
          }
          /* Call the function and pass ownership of data to it */
          COVER_best_start(&best);
          if (pool) {
            POOL_add(pool, &FASTCOVER_tryParameters, data);
          } else {
            FASTCOVER_tryParameters(data);
          }
          /* Print status */
          LOCALDISPLAYUPDATE(displayLevel, 2, "\r%u%%       ",
                             (unsigned)((iteration * 100) / kIterations));
          ++iteration;
        }
        COVER_best_wait(&best);
        FASTCOVER_ctx_destroy(&ctx);
      }
      LOCALDISPLAYLEVEL(displayLevel, 2, "\r%79s\r", "");
      /* Fill the output buffer and parameters with output of the best parameters */
      {
        const size_t dictSize = best.dictSize;
        if (ZSTD_isError(best.compressedSize)) {
          const size_t compressedSize = best.compressedSize;
          COVER_best_destroy(&best);
          POOL_free(pool);
          return compressedSize;
        }
        FASTCOVER_convertToFastCoverParams(best.parameters, parameters, f, accel);
        memcpy(dictBuffer, best.dict, dictSize);
        COVER_best_destroy(&best);
        POOL_free(pool);
        return dictSize;
      }
  
  }
  