comparison contrib/python-zstandard/zstd/dictBuilder/fastcover.c @ 40121:73fef626dae3

zstandard: vendor python-zstandard 0.10.1

This was just released.

The upstream source distribution from PyPI was extracted. Unwanted
files were removed.

The clang-format ignore list was updated to reflect the new source
of files.

setup.py was updated to pass a new argument to python-zstandard's
function for returning an Extension instance. Upstream had to change
to use relative paths because Python 3.7's packaging doesn't
seem to like absolute paths when defining sources, includes, etc.
The default relative path calculation is relative to setup_zstd.py
which is different from the directory of Mercurial's setup.py.

The project contains a vendored copy of zstandard 1.3.6. The old
version was 1.3.4.

The API should be backwards compatible and nothing in core should
need adjusted. However, there is a new "chunker" API that we
may find useful in places where we want to emit compressed chunks
of a fixed size.

There are a pair of bug fixes in 0.10.0 with regards to
compressobj() and decompressobj() when block flushing is used. I
actually found these bugs when introducing these APIs in Mercurial!
But existing Mercurial code is not affected because we don't
perform block flushing.

# no-check-commit because 3rd party code has different style guidelines

Differential Revision: https://phab.mercurial-scm.org/D4911

40121:73fef626dae3

/*-*************************************
*  Dependencies
***************************************/
#include <stdio.h>  /* fprintf */
#include <stdlib.h> /* malloc, free, qsort */
#include <string.h> /* memset */
#include <time.h>   /* clock */

#include "mem.h" /* read */
#include "pool.h"
#include "threading.h"
#include "cover.h"
#include "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 ? ((U32)-1) : ((U32)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 dictionay 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 index = FASTCOVER_hashPtrToIndex(ctx->samples + activeSegment.end, f, d);

    /* Add frequency of this index to score if this is the first occurence of index in active segment */
    if (segmentFreqs[index] == 0) {
      activeSegment.score += freqs[index];
    }
    /* Increment end of segment and segmentFreqs*/
    activeSegment.end += 1;
    segmentFreqs[index] += 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) {
    return 0;
  }
  /* d has to be 6 or 8 */
  if (parameters.d != 6 && parameters.d != 8) {
    return 0;
  }
  /* k <= maxDictSize */
  if (parameters.k > maxDictSize) {
    return 0;
  }
  /* d <= k */
  if (parameters.d > parameters.k) {
    return 0;
  }
  /* 0 < f <= FASTCOVER_MAX_F*/
  if (f > FASTCOVER_MAX_F || f == 0) {
    return 0;
  }
  /* 0 < splitPoint <= 1 */
  if (parameters.splitPoint <= 0 || parameters.splitPoint > 1) {
    return 0;
  }
  /* 0 < accel <= 10 */
  if (accel > 10 || accel == 0) {
    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 1 on success or zero on error.
 * The context must be destroyed with `FASTCOVER_ctx_destroy()`.
 */
static int
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",
                    (U32)(totalSamplesSize >> 20), (FASTCOVER_MAX_SAMPLES_SIZE >> 20));
        return 0;
    }

    /* 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 0;
    }

    /* Check if there's testing sample */
    if (nbTestSamples < 1) {
        DISPLAYLEVEL(1, "Total number of testing samples is %u and is invalid.\n", nbTestSamples);
        return 0;
    }

    /* Zero the context */
    memset(ctx, 0, sizeof(*ctx));
    DISPLAYLEVEL(2, "Training on %u samples of total size %u\n", nbTrainSamples,
                    (U32)trainingSamplesSize);
    DISPLAYLEVEL(2, "Testing on %u samples of total size %u\n", nbTestSamples,
                    (U32)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 0;
    }

    /* 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 0;
    }

    DISPLAYLEVEL(2, "Computing frequencies\n");
    FASTCOVER_computeFrequency(ctx->freqs, ctx);

    return 1;
}


/**
 * 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 up into epochs of equal size.
   * We will select at least one segment from each epoch.
   */
  const U32 epochs = MAX(1, (U32)(dictBufferCapacity / parameters.k));
  const U32 epochSize = (U32)(ctx->nbDmers / epochs);
  size_t epoch;
  DISPLAYLEVEL(2, "Breaking content into %u epochs of size %u\n", epochs,
               epochSize);
  /* Loop through the epochs until there are no more segments or the dictionary
   * is full.
   */
  for (epoch = 0; tail > 0; epoch = (epoch + 1) % epochs) {
    const U32 epochBegin = (U32)(epoch * epochSize);
    const U32 epochEnd = epochBegin + epochSize;
    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 */
    if (segment.score == 0) {
      break;
    }

    /* 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%%       ",
        (U32)(((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);
  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);
    dictBufferCapacity = ZDICT_finalizeDictionary(
        dict, dictBufferCapacity, dict + tail, dictBufferCapacity - tail,
        ctx->samples, ctx->samplesSizes, nbFinalizeSamples, parameters.zParams);
    if (ZDICT_isError(dictBufferCapacity)) {
      DISPLAYLEVEL(1, "Failed to finalize dictionary\n");
      goto _cleanup;
    }
  }
  /* Check total compressed size */
  totalCompressedSize = COVER_checkTotalCompressedSize(parameters, ctx->samplesSizes,
                                                       ctx->samples, ctx->offsets,
                                                       ctx->nbTrainSamples, ctx->nbSamples,
                                                       dict, dictBufferCapacity);
_cleanup:
  COVER_best_finish(data->best, totalCompressedSize, parameters, dict,
                    dictBufferCapacity);
  free(data);
  free(segmentFreqs);
  free(dict);
  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;
}


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;
}


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(GENERIC);
    }
    if (nbSamples == 0) {
      DISPLAYLEVEL(1, "FASTCOVER must have at least one input file\n");
      return ERROR(GENERIC);
    }
    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 */
    if (!FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples,
                            coverParams.d, parameters.splitPoint, parameters.f,
                            accelParams)) {
      DISPLAYLEVEL(1, "Failed to initialize context\n");
      return ERROR(GENERIC);
    }
    /* 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",
                      (U32)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;
    /* Local variables */
    const int displayLevel = parameters->zParams.notificationLevel;
    unsigned iteration = 1;
    unsigned d;
    unsigned k;
    COVER_best_t best;
    POOL_ctx *pool = NULL;
    /* Checks */
    if (splitPoint <= 0 || splitPoint > 1) {
      LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect splitPoint\n");
      return ERROR(GENERIC);
    }
    if (accel == 0 || accel > FASTCOVER_MAX_ACCEL) {
      LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect accel\n");
      return ERROR(GENERIC);
    }
    if (kMinK < kMaxD || kMaxK < kMinK) {
      LOCALDISPLAYLEVEL(displayLevel, 1, "Incorrect k\n");
      return ERROR(GENERIC);
    }
    if (nbSamples == 0) {
      LOCALDISPLAYLEVEL(displayLevel, 1, "FASTCOVER must have at least one input file\n");
      return ERROR(GENERIC);
    }
    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);
      if (!FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples, d, splitPoint, f, accelParams)) {
        LOCALDISPLAYLEVEL(displayLevel, 1, "Failed to initialize context\n");
        COVER_best_destroy(&best);
        POOL_free(pool);
        return ERROR(GENERIC);
      }
      /* 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(GENERIC);
        }
        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.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%%       ",
                           (U32)((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;
    }

}