zstd/contrib/largeNbDicts/largeNbDicts.c

/*
 * Copyright (c) 2018-present, Yann Collet, 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.
 */

/* largeNbDicts
 * This is a benchmark test tool
 * dedicated to the specific case of dictionary decompression
 * using a very large nb of dictionaries
 * thus suffering latency from lots of cache misses.
 * It's created in a bid to investigate performance and find optimizations. */


/*---  Dependencies  ---*/

#include <stddef.h>   /* size_t */
#include <stdlib.h>   /* malloc, free, abort */
#include <stdio.h>    /* fprintf */
#include <assert.h>   /* assert */

#include "util.h"
#include "benchfn.h"
#define ZSTD_STATIC_LINKING_ONLY
#include "zstd.h"
#include "zdict.h"


/*---  Constants  --- */

#define KB  *(1<<10)
#define MB  *(1<<20)

#define BLOCKSIZE_DEFAULT 0  /* no slicing into blocks */
#define DICTSIZE  (4 KB)
#define CLEVEL_DEFAULT 3

#define BENCH_TIME_DEFAULT_S   6
#define RUN_TIME_DEFAULT_MS    1000
#define BENCH_TIME_DEFAULT_MS (BENCH_TIME_DEFAULT_S * RUN_TIME_DEFAULT_MS)

#define DISPLAY_LEVEL_DEFAULT 3

#define BENCH_SIZE_MAX (1200 MB)


/*---  Macros  ---*/

#define CONTROL(c)   { if (!(c)) abort(); }
#undef MIN
#define MIN(a,b)     ((a) < (b) ? (a) : (b))


/*---  Display Macros  ---*/

#define DISPLAY(...)         fprintf(stdout, __VA_ARGS__)
#define DISPLAYLEVEL(l, ...) { if (g_displayLevel>=l) { DISPLAY(__VA_ARGS__); } }
static int g_displayLevel = DISPLAY_LEVEL_DEFAULT;   /* 0 : no display,  1: errors,  2 : + result + interaction + warnings,  3 : + progression,  4 : + information */


/*---  buffer_t  ---*/

typedef struct {
    void* ptr;
    size_t size;
    size_t capacity;
} buffer_t;

static const buffer_t kBuffNull = { NULL, 0, 0 };

/* @return : kBuffNull if any error */
static buffer_t createBuffer(size_t capacity)
{
    assert(capacity > 0);
    void* const ptr = malloc(capacity);
    if (ptr==NULL) return kBuffNull;

    buffer_t buffer;
    buffer.ptr = ptr;
    buffer.capacity = capacity;
    buffer.size = 0;
    return buffer;
}

static void freeBuffer(buffer_t buff)
{
    free(buff.ptr);
}


static void fillBuffer_fromHandle(buffer_t* buff, FILE* f)
{
    size_t const readSize = fread(buff->ptr, 1, buff->capacity, f);
    buff->size = readSize;
}


/* @return : kBuffNull if any error */
static buffer_t createBuffer_fromFile(const char* fileName)
{
    U64 const fileSize = UTIL_getFileSize(fileName);
    size_t const bufferSize = (size_t) fileSize;

    if (fileSize == UTIL_FILESIZE_UNKNOWN) return kBuffNull;
    assert((U64)bufferSize == fileSize);   /* check overflow */

    {   FILE* const f = fopen(fileName, "rb");
        if (f == NULL) return kBuffNull;

        buffer_t buff = createBuffer(bufferSize);
        CONTROL(buff.ptr != NULL);

        fillBuffer_fromHandle(&buff, f);
        CONTROL(buff.size == buff.capacity);

        fclose(f);   /* do nothing specific if fclose() fails */
        return buff;
    }
}


/* @return : kBuffNull if any error */
static buffer_t
createDictionaryBuffer(const char* dictionaryName,
                       const void* srcBuffer,
                       const size_t* srcBlockSizes, unsigned nbBlocks,
                       size_t requestedDictSize)
{
    if (dictionaryName) {
        DISPLAYLEVEL(3, "loading dictionary %s \n", dictionaryName);
        return createBuffer_fromFile(dictionaryName);  /* note : result might be kBuffNull */

    } else {

        DISPLAYLEVEL(3, "creating dictionary, of target size %u bytes \n",
                        (unsigned)requestedDictSize);
        void* const dictBuffer = malloc(requestedDictSize);
        CONTROL(dictBuffer != NULL);

        size_t const dictSize = ZDICT_trainFromBuffer(dictBuffer, requestedDictSize,
                                                      srcBuffer,
                                                      srcBlockSizes, nbBlocks);
        CONTROL(!ZSTD_isError(dictSize));

        buffer_t result;
        result.ptr = dictBuffer;
        result.capacity = requestedDictSize;
        result.size = dictSize;
        return result;
    }
}


/*! BMK_loadFiles() :
 *  Loads `buffer`, with content from files listed within `fileNamesTable`.
 *  Fills `buffer` entirely.
 * @return : 0 on success, !=0 on error */
static int loadFiles(void* buffer, size_t bufferSize,
                     size_t* fileSizes,
                     const char* const * fileNamesTable, unsigned nbFiles)
{
    size_t pos = 0, totalSize = 0;

    for (unsigned n=0; n<nbFiles; n++) {
        U64 fileSize = UTIL_getFileSize(fileNamesTable[n]);
        if (UTIL_isDirectory(fileNamesTable[n])) {
            fileSizes[n] = 0;
            continue;
        }
        if (fileSize == UTIL_FILESIZE_UNKNOWN) {
            fileSizes[n] = 0;
            continue;
        }

        FILE* const f = fopen(fileNamesTable[n], "rb");
        assert(f!=NULL);

        assert(pos <= bufferSize);
        assert(fileSize <= bufferSize - pos);

        {   size_t const readSize = fread(((char*)buffer)+pos, 1, (size_t)fileSize, f);
            assert(readSize == fileSize);
            pos += readSize;
        }
        fileSizes[n] = (size_t)fileSize;
        totalSize += (size_t)fileSize;
        fclose(f);
    }

    assert(totalSize == bufferSize);
    return 0;
}



/*---  slice_collection_t  ---*/

typedef struct {
    void** slicePtrs;
    size_t* capacities;
    size_t nbSlices;
} slice_collection_t;

static const slice_collection_t kNullCollection = { NULL, NULL, 0 };

static void freeSliceCollection(slice_collection_t collection)
{
    free(collection.slicePtrs);
    free(collection.capacities);
}

/* shrinkSizes() :
 * downsizes sizes of slices within collection, according to `newSizes`.
 * every `newSizes` entry must be <= than its corresponding collection size */
void shrinkSizes(slice_collection_t collection,
                 const size_t* newSizes)  /* presumed same size as collection */
{
    size_t const nbSlices = collection.nbSlices;
    for (size_t blockNb = 0; blockNb < nbSlices; blockNb++) {
        assert(newSizes[blockNb] <= collection.capacities[blockNb]);
        collection.capacities[blockNb] = newSizes[blockNb];
    }
}


/* splitSlices() :
 * nbSlices : if == 0, nbSlices is automatically determined from srcSlices and blockSize.
 *            otherwise, creates exactly nbSlices slices,
 *            by either truncating input (when smaller)
 *            or repeating input from beginning */
static slice_collection_t
splitSlices(slice_collection_t srcSlices, size_t blockSize, size_t nbSlices)
{
    if (blockSize==0) blockSize = (size_t)(-1);   /* means "do not cut" */
    size_t nbSrcBlocks = 0;
    for (size_t ssnb=0; ssnb < srcSlices.nbSlices; ssnb++) {
        size_t pos = 0;
        while (pos <= srcSlices.capacities[ssnb]) {
            nbSrcBlocks++;
            pos += blockSize;
        }
    }

    if (nbSlices == 0) nbSlices = nbSrcBlocks;

    void** const sliceTable = (void**)malloc(nbSlices * sizeof(*sliceTable));
    size_t* const capacities = (size_t*)malloc(nbSlices * sizeof(*capacities));
    if (sliceTable == NULL || capacities == NULL) {
        free(sliceTable);
        free(capacities);
        return kNullCollection;
    }

    size_t ssnb = 0;
    for (size_t sliceNb=0; sliceNb < nbSlices; ) {
        ssnb = (ssnb + 1) % srcSlices.nbSlices;
        size_t pos = 0;
        char* const ptr = (char*)srcSlices.slicePtrs[ssnb];
        while (pos < srcSlices.capacities[ssnb] && sliceNb < nbSlices) {
            size_t const size = MIN(blockSize, srcSlices.capacities[ssnb] - pos);
            sliceTable[sliceNb] = ptr + pos;
            capacities[sliceNb] = size;
            sliceNb++;
            pos += blockSize;
        }
    }

    slice_collection_t result;
    result.nbSlices = nbSlices;
    result.slicePtrs = sliceTable;
    result.capacities = capacities;
    return result;
}


static size_t sliceCollection_totalCapacity(slice_collection_t sc)
{
    size_t totalSize = 0;
    for (size_t n=0; n<sc.nbSlices; n++)
        totalSize += sc.capacities[n];
    return totalSize;
}


/* ---  buffer collection  --- */

typedef struct {
    buffer_t buffer;
    slice_collection_t slices;
} buffer_collection_t;


static void freeBufferCollection(buffer_collection_t bc)
{
    freeBuffer(bc.buffer);
    freeSliceCollection(bc.slices);
}


static buffer_collection_t
createBufferCollection_fromSliceCollectionSizes(slice_collection_t sc)
{
    size_t const bufferSize = sliceCollection_totalCapacity(sc);

    buffer_t buffer = createBuffer(bufferSize);
    CONTROL(buffer.ptr != NULL);

    size_t const nbSlices = sc.nbSlices;
    void** const slices = (void**)malloc(nbSlices * sizeof(*slices));
    CONTROL(slices != NULL);

    size_t* const capacities = (size_t*)malloc(nbSlices * sizeof(*capacities));
    CONTROL(capacities != NULL);

    char* const ptr = (char*)buffer.ptr;
    size_t pos = 0;
    for (size_t n=0; n < nbSlices; n++) {
        capacities[n] = sc.capacities[n];
        slices[n] = ptr + pos;
        pos += capacities[n];
    }

    buffer_collection_t result;
    result.buffer = buffer;
    result.slices.nbSlices = nbSlices;
    result.slices.capacities = capacities;
    result.slices.slicePtrs = slices;
    return result;
}


/* @return : kBuffNull if any error */
static buffer_collection_t
createBufferCollection_fromFiles(const char* const * fileNamesTable, unsigned nbFiles)
{
    U64 const totalSizeToLoad = UTIL_getTotalFileSize(fileNamesTable, nbFiles);
    assert(totalSizeToLoad != UTIL_FILESIZE_UNKNOWN);
    assert(totalSizeToLoad <= BENCH_SIZE_MAX);
    size_t const loadedSize = (size_t)totalSizeToLoad;
    assert(loadedSize > 0);
    void* const srcBuffer = malloc(loadedSize);
    assert(srcBuffer != NULL);

    assert(nbFiles > 0);
    size_t* const fileSizes = (size_t*)calloc(nbFiles, sizeof(*fileSizes));
    assert(fileSizes != NULL);

    /* Load input buffer */
    int const errorCode = loadFiles(srcBuffer, loadedSize,
                                    fileSizes,
                                    fileNamesTable, nbFiles);
    assert(errorCode == 0);

    void** sliceTable = (void**)malloc(nbFiles * sizeof(*sliceTable));
    assert(sliceTable != NULL);

    char* const ptr = (char*)srcBuffer;
    size_t pos = 0;
    unsigned fileNb = 0;
    for ( ; (pos < loadedSize) && (fileNb < nbFiles); fileNb++) {
        sliceTable[fileNb] = ptr + pos;
        pos += fileSizes[fileNb];
    }
    assert(pos == loadedSize);
    assert(fileNb == nbFiles);


    buffer_t buffer;
    buffer.ptr = srcBuffer;
    buffer.capacity = loadedSize;
    buffer.size = loadedSize;

    slice_collection_t slices;
    slices.slicePtrs = sliceTable;
    slices.capacities = fileSizes;
    slices.nbSlices = nbFiles;

    buffer_collection_t bc;
    bc.buffer = buffer;
    bc.slices = slices;
    return bc;
}




/*---  ddict_collection_t  ---*/

typedef struct {
    ZSTD_DDict** ddicts;
    size_t nbDDict;
} ddict_collection_t;

static const ddict_collection_t kNullDDictCollection = { NULL, 0 };

static void freeDDictCollection(ddict_collection_t ddictc)
{
    for (size_t dictNb=0; dictNb < ddictc.nbDDict; dictNb++) {
        ZSTD_freeDDict(ddictc.ddicts[dictNb]);
    }
    free(ddictc.ddicts);
}

/* returns .buffers=NULL if operation fails */
static ddict_collection_t createDDictCollection(const void* dictBuffer, size_t dictSize, size_t nbDDict)
{
    ZSTD_DDict** const ddicts = malloc(nbDDict * sizeof(ZSTD_DDict*));
    assert(ddicts != NULL);
    if (ddicts==NULL) return kNullDDictCollection;
    for (size_t dictNb=0; dictNb < nbDDict; dictNb++) {
        ddicts[dictNb] = ZSTD_createDDict(dictBuffer, dictSize);
        assert(ddicts[dictNb] != NULL);
    }
    ddict_collection_t ddictc;
    ddictc.ddicts = ddicts;
    ddictc.nbDDict = nbDDict;
    return ddictc;
}


/* mess with adresses, so that linear scanning dictionaries != linear address scanning */
void shuffleDictionaries(ddict_collection_t dicts)
{
    size_t const nbDicts = dicts.nbDDict;
    for (size_t r=0; r<nbDicts; r++) {
        size_t const d = rand() % nbDicts;
        ZSTD_DDict* tmpd = dicts.ddicts[d];
        dicts.ddicts[d] = dicts.ddicts[r];
        dicts.ddicts[r] = tmpd;
    }
    for (size_t r=0; r<nbDicts; r++) {
        size_t const d1 = rand() % nbDicts;
        size_t const d2 = rand() % nbDicts;
        ZSTD_DDict* tmpd = dicts.ddicts[d1];
        dicts.ddicts[d1] = dicts.ddicts[d2];
        dicts.ddicts[d2] = tmpd;
    }
}


/* ---   Compression  --- */

/* compressBlocks() :
 * @return : total compressed size of all blocks,
 *        or 0 if error.
 */
static size_t compressBlocks(size_t* cSizes,   /* optional (can be NULL). If present, must contain at least nbBlocks fields */
                             slice_collection_t dstBlockBuffers,
                             slice_collection_t srcBlockBuffers,
                             ZSTD_CDict* cdict, int cLevel)
{
    size_t const nbBlocks = srcBlockBuffers.nbSlices;
    assert(dstBlockBuffers.nbSlices == srcBlockBuffers.nbSlices);

    ZSTD_CCtx* const cctx = ZSTD_createCCtx();
    assert(cctx != NULL);

    size_t totalCSize = 0;
    for (size_t blockNb=0; blockNb < nbBlocks; blockNb++) {
        size_t cBlockSize;
        if (cdict == NULL) {
            cBlockSize = ZSTD_compressCCtx(cctx,
                            dstBlockBuffers.slicePtrs[blockNb], dstBlockBuffers.capacities[blockNb],
                            srcBlockBuffers.slicePtrs[blockNb], srcBlockBuffers.capacities[blockNb],
                            cLevel);
        } else {
            cBlockSize = ZSTD_compress_usingCDict(cctx,
                            dstBlockBuffers.slicePtrs[blockNb], dstBlockBuffers.capacities[blockNb],
                            srcBlockBuffers.slicePtrs[blockNb], srcBlockBuffers.capacities[blockNb],
                            cdict);
        }
        CONTROL(!ZSTD_isError(cBlockSize));
        if (cSizes) cSizes[blockNb] = cBlockSize;
        totalCSize += cBlockSize;
    }
    return totalCSize;
}


/* ---  Benchmark  --- */

typedef struct {
    ZSTD_DCtx* dctx;
    size_t nbDicts;
    size_t dictNb;
    ddict_collection_t dictionaries;
} decompressInstructions;

decompressInstructions createDecompressInstructions(ddict_collection_t dictionaries)
{
    decompressInstructions di;
    di.dctx = ZSTD_createDCtx();
    assert(di.dctx != NULL);
    di.nbDicts = dictionaries.nbDDict;
    di.dictNb = 0;
    di.dictionaries = dictionaries;
    return di;
}

void freeDecompressInstructions(decompressInstructions di)
{
    ZSTD_freeDCtx(di.dctx);
}

/* benched function */
size_t decompress(const void* src, size_t srcSize, void* dst, size_t dstCapacity, void* payload)
{
    decompressInstructions* const di = (decompressInstructions*) payload;

    size_t const result = ZSTD_decompress_usingDDict(di->dctx,
                                        dst, dstCapacity,
                                        src, srcSize,
                                        di->dictionaries.ddicts[di->dictNb]);

    di->dictNb = di->dictNb + 1;
    if (di->dictNb >= di->nbDicts) di->dictNb = 0;

    return result;
}


static int benchMem(slice_collection_t dstBlocks,
                    slice_collection_t srcBlocks,
                    ddict_collection_t dictionaries,
                    int nbRounds)
{
    assert(dstBlocks.nbSlices == srcBlocks.nbSlices);

    unsigned const ms_per_round = RUN_TIME_DEFAULT_MS;
    unsigned const total_time_ms = nbRounds * ms_per_round;

    double bestSpeed = 0.;

    BMK_timedFnState_t* const benchState =
            BMK_createTimedFnState(total_time_ms, ms_per_round);
    decompressInstructions di = createDecompressInstructions(dictionaries);
    BMK_benchParams_t const bp = {
        .benchFn = decompress,
        .benchPayload = &di,
        .initFn = NULL,
        .initPayload = NULL,
        .errorFn = ZSTD_isError,
        .blockCount = dstBlocks.nbSlices,
        .srcBuffers = (const void* const*) srcBlocks.slicePtrs,
        .srcSizes = srcBlocks.capacities,
        .dstBuffers = dstBlocks.slicePtrs,
        .dstCapacities = dstBlocks.capacities,
        .blockResults = NULL
    };

    for (;;) {
        BMK_runOutcome_t const outcome = BMK_benchTimedFn(benchState, bp);
        CONTROL(BMK_isSuccessful_runOutcome(outcome));

        BMK_runTime_t const result = BMK_extract_runTime(outcome);
        U64 const dTime_ns = result.nanoSecPerRun;
        double const dTime_sec = (double)dTime_ns / 1000000000;
        size_t const srcSize = result.sumOfReturn;
        double const dSpeed_MBps = (double)srcSize / dTime_sec / (1 MB);
        if (dSpeed_MBps > bestSpeed) bestSpeed = dSpeed_MBps;
        DISPLAY("Decompression Speed : %.1f MB/s \r", bestSpeed);
        fflush(stdout);
        if (BMK_isCompleted_TimedFn(benchState)) break;
    }
    DISPLAY("\n");

    freeDecompressInstructions(di);
    BMK_freeTimedFnState(benchState);

    return 0;   /* success */
}


/*! bench() :
 *  fileName : file to load for benchmarking purpose
 *  dictionary : optional (can be NULL), file to load as dictionary,
 *              if none provided : will be calculated on the fly by the program.
 * @return : 0 is success, 1+ otherwise */
int bench(const char** fileNameTable, unsigned nbFiles,
          const char* dictionary,
          size_t blockSize, int clevel,
          unsigned nbDictMax, unsigned nbBlocks,
          int nbRounds)
{
    int result = 0;

    DISPLAYLEVEL(3, "loading %u files... \n", nbFiles);
    buffer_collection_t const srcs = createBufferCollection_fromFiles(fileNameTable, nbFiles);
    CONTROL(srcs.buffer.ptr != NULL);
    buffer_t srcBuffer = srcs.buffer;
    size_t const srcSize = srcBuffer.size;
    DISPLAYLEVEL(3, "created src buffer of size %.1f MB \n",
                    (double)srcSize / (1 MB));

    slice_collection_t const srcSlices = splitSlices(srcs.slices, blockSize, nbBlocks);
    nbBlocks = (unsigned)(srcSlices.nbSlices);
    DISPLAYLEVEL(3, "split input into %u blocks ", nbBlocks);
    if (blockSize)
        DISPLAYLEVEL(3, "of max size %u bytes ", (unsigned)blockSize);
    DISPLAYLEVEL(3, "\n");
    size_t const totalSrcSlicesSize = sliceCollection_totalCapacity(srcSlices);


    size_t* const dstCapacities = malloc(nbBlocks * sizeof(*dstCapacities));
    CONTROL(dstCapacities != NULL);
    size_t dstBufferCapacity = 0;
    for (size_t bnb=0; bnb<nbBlocks; bnb++) {
        dstCapacities[bnb] = ZSTD_compressBound(srcSlices.capacities[bnb]);
        dstBufferCapacity += dstCapacities[bnb];
    }

    buffer_t dstBuffer = createBuffer(dstBufferCapacity);
    CONTROL(dstBuffer.ptr != NULL);

    void** const sliceTable = malloc(nbBlocks * sizeof(*sliceTable));
    CONTROL(sliceTable != NULL);

    {   char* const ptr = dstBuffer.ptr;
        size_t pos = 0;
        for (size_t snb=0; snb < nbBlocks; snb++) {
            sliceTable[snb] = ptr + pos;
            pos += dstCapacities[snb];
    }   }

    slice_collection_t dstSlices;
    dstSlices.capacities = dstCapacities;
    dstSlices.slicePtrs = sliceTable;
    dstSlices.nbSlices = nbBlocks;


    /* dictionary determination */
    buffer_t const dictBuffer = createDictionaryBuffer(dictionary,
                                srcs.buffer.ptr,
                                srcs.slices.capacities, srcs.slices.nbSlices,
                                DICTSIZE);
    CONTROL(dictBuffer.ptr != NULL);

    ZSTD_CDict* const cdict = ZSTD_createCDict(dictBuffer.ptr, dictBuffer.size, clevel);
    CONTROL(cdict != NULL);

    size_t const cTotalSizeNoDict = compressBlocks(NULL, dstSlices, srcSlices, NULL, clevel);
    CONTROL(cTotalSizeNoDict != 0);
    DISPLAYLEVEL(3, "compressing at level %u without dictionary : Ratio=%.2f  (%u bytes) \n",
                    clevel,
                    (double)totalSrcSlicesSize / cTotalSizeNoDict, (unsigned)cTotalSizeNoDict);

    size_t* const cSizes = malloc(nbBlocks * sizeof(size_t));
    CONTROL(cSizes != NULL);

    size_t const cTotalSize = compressBlocks(cSizes, dstSlices, srcSlices, cdict, clevel);
    CONTROL(cTotalSize != 0);
    DISPLAYLEVEL(3, "compressed using a %u bytes dictionary : Ratio=%.2f  (%u bytes) \n",
                    (unsigned)dictBuffer.size,
                    (double)totalSrcSlicesSize / cTotalSize, (unsigned)cTotalSize);

    /* now dstSlices contain the real compressed size of each block, instead of the maximum capacity */
    shrinkSizes(dstSlices, cSizes);

    size_t const dictMem = ZSTD_estimateDDictSize(dictBuffer.size, ZSTD_dlm_byCopy);
    unsigned const nbDicts = nbDictMax ? nbDictMax : nbBlocks;
    size_t const allDictMem = dictMem * nbDicts;
    DISPLAYLEVEL(3, "generating %u dictionaries, using %.1f MB of memory \n",
                    nbDicts, (double)allDictMem / (1 MB));

    ddict_collection_t const dictionaries = createDDictCollection(dictBuffer.ptr, dictBuffer.size, nbDicts);
    CONTROL(dictionaries.ddicts != NULL);

    shuffleDictionaries(dictionaries);

    buffer_collection_t resultCollection = createBufferCollection_fromSliceCollectionSizes(srcSlices);
    CONTROL(resultCollection.buffer.ptr != NULL);

    result = benchMem(resultCollection.slices, dstSlices, dictionaries, nbRounds);

    /* free all heap objects in reverse order */
    freeBufferCollection(resultCollection);
    freeDDictCollection(dictionaries);
    free(cSizes);
    ZSTD_freeCDict(cdict);
    freeBuffer(dictBuffer);
    freeSliceCollection(dstSlices);
    freeBuffer(dstBuffer);
    freeSliceCollection(srcSlices);
    freeBufferCollection(srcs);

    return result;
}



/* ---  Command Line  --- */

/*! readU32FromChar() :
 * @return : unsigned integer value read from input in `char` format.
 *  allows and interprets K, KB, KiB, M, MB and MiB suffix.
 *  Will also modify `*stringPtr`, advancing it to position where it stopped reading.
 *  Note : function will exit() program if digit sequence overflows */
static unsigned readU32FromChar(const char** stringPtr)
{
    unsigned result = 0;
    while ((**stringPtr >='0') && (**stringPtr <='9')) {
        unsigned const max = (((unsigned)(-1)) / 10) - 1;
        assert(result <= max);   /* check overflow */
        result *= 10, result += **stringPtr - '0', (*stringPtr)++ ;
    }
    if ((**stringPtr=='K') || (**stringPtr=='M')) {
        unsigned const maxK = ((unsigned)(-1)) >> 10;
        assert(result <= maxK);   /* check overflow */
        result <<= 10;
        if (**stringPtr=='M') {
            assert(result <= maxK);   /* check overflow */
            result <<= 10;
        }
        (*stringPtr)++;  /* skip `K` or `M` */
        if (**stringPtr=='i') (*stringPtr)++;
        if (**stringPtr=='B') (*stringPtr)++;
    }
    return result;
}

/** longCommandWArg() :
 *  check if *stringPtr is the same as longCommand.
 *  If yes, @return 1 and advances *stringPtr to the position which immediately follows longCommand.
 * @return 0 and doesn't modify *stringPtr otherwise.
 */
static unsigned longCommandWArg(const char** stringPtr, const char* longCommand)
{
    size_t const comSize = strlen(longCommand);
    int const result = !strncmp(*stringPtr, longCommand, comSize);
    if (result) *stringPtr += comSize;
    return result;
}


int usage(const char* exeName)
{
    DISPLAY (" \n");
    DISPLAY (" %s [Options] filename(s) \n", exeName);
    DISPLAY (" \n");
    DISPLAY ("Options : \n");
    DISPLAY ("-r          : recursively load all files in subdirectories (default: off) \n");
    DISPLAY ("-B#         : split input into blocks of size # (default: no split) \n");
    DISPLAY ("-#          : use compression level # (default: %u) \n", CLEVEL_DEFAULT);
    DISPLAY ("-D #        : use # as a dictionary (default: create one) \n");
    DISPLAY ("-i#         : nb benchmark rounds (default: %u) \n", BENCH_TIME_DEFAULT_S);
    DISPLAY ("--nbBlocks=#: use # blocks for bench (default: one per file) \n");
    DISPLAY ("--nbDicts=# : create # dictionaries for bench (default: one per block) \n");
    DISPLAY ("-h          : help (this text) \n");
    return 0;
}

int bad_usage(const char* exeName)
{
    DISPLAY (" bad usage : \n");
    usage(exeName);
    return 1;
}

int main (int argc, const char** argv)
{
    int recursiveMode = 0;
    int nbRounds = BENCH_TIME_DEFAULT_S;
    const char* const exeName = argv[0];

    if (argc < 2) return bad_usage(exeName);

    const char** nameTable = (const char**)malloc(argc * sizeof(const char*));
    assert(nameTable != NULL);
    unsigned nameIdx = 0;

    const char* dictionary = NULL;
    int cLevel = CLEVEL_DEFAULT;
    size_t blockSize = BLOCKSIZE_DEFAULT;
    unsigned nbDicts = 0;  /* determine nbDicts automatically: 1 dictionary per block */
    unsigned nbBlocks = 0; /* determine nbBlocks automatically, from source and blockSize */

    for (int argNb = 1; argNb < argc ; argNb++) {
        const char* argument = argv[argNb];
        if (!strcmp(argument, "-h")) { free(nameTable); return usage(exeName); }
        if (!strcmp(argument, "-r")) { recursiveMode = 1; continue; }
        if (!strcmp(argument, "-D")) { argNb++; assert(argNb < argc); dictionary = argv[argNb]; continue; }
        if (longCommandWArg(&argument, "-i")) { nbRounds = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "--dictionary=")) { dictionary = argument; continue; }
        if (longCommandWArg(&argument, "-B")) { blockSize = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "--blockSize=")) { blockSize = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "--nbDicts=")) { nbDicts = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "--nbBlocks=")) { nbBlocks = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "--clevel=")) { cLevel = readU32FromChar(&argument); continue; }
        if (longCommandWArg(&argument, "-")) { cLevel = readU32FromChar(&argument); continue; }
        /* anything that's not a command is a filename */
        nameTable[nameIdx++] = argument;
    }

    const char** filenameTable = nameTable;
    unsigned nbFiles = nameIdx;
    char* buffer_containing_filenames = NULL;

    if (recursiveMode) {
#ifndef UTIL_HAS_CREATEFILELIST
        assert(0);   /* missing capability, do not run */
#endif
        filenameTable = UTIL_createFileList(nameTable, nameIdx, &buffer_containing_filenames, &nbFiles, 1 /* follow_links */);
    }

    int result = bench(filenameTable, nbFiles, dictionary, blockSize, cLevel, nbDicts, nbBlocks, nbRounds);

    free(buffer_containing_filenames);
    free(nameTable);

    return result;
}