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Improve optimal parser performance on small data #2771

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merged 16 commits into from
Sep 14, 2021
Merged

Improve optimal parser performance on small data #2771

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eab6922
removed pretty-print of sizes in benchmark
Cyan4973 Sep 3, 2021
f0fc8cb
Disable console notification by default within the library
Cyan4973 Sep 3, 2021
27a8bbe
new initializer for ll price
Cyan4973 Sep 3, 2021
23a9368
new starting offcode table for zstd_opt
Cyan4973 Sep 4, 2021
08ceda3
new statistics update policy
Cyan4973 Sep 4, 2021
b096a5c
updated regression tests
Cyan4973 Sep 7, 2021
42a3ed7
removed frequency booster for stat initialization of btultra2
Cyan4973 Sep 8, 2021
ef78611
change update rate to 11/10/10/10
Cyan4973 Sep 8, 2021
7fce9a4
change update rate to 12/11/11/11
Cyan4973 Sep 8, 2021
4f0b1b9
update regression tests
Cyan4973 Sep 8, 2021
b7f46eb
use ZSTD_memcpy() for better portability
Cyan4973 Sep 8, 2021
5449ede
make automated-benchmarking faster
Cyan4973 Sep 8, 2021
640c5b1
fix automated_benchmarking
Cyan4973 Sep 12, 2021
f58e63b
Merge branch 'dev' into opt_investigation
Cyan4973 Sep 12, 2021
b6b2855
updated regression tests
Cyan4973 Sep 12, 2021
fd94b9d
Merge branch 'dev' into opt_investigation
Cyan4973 Sep 14, 2021
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121 changes: 64 additions & 57 deletions lib/compress/zstd_opt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@


#define ZSTD_LITFREQ_ADD 2 /* scaling factor for litFreq, so that frequencies adapt faster to new stats */
#define ZSTD_FREQ_DIV 4 /* log factor when using previous stats to init next stats */
#define ZSTD_MAX_PRICE (1<<30)

#define ZSTD_PREDEF_THRESHOLD 1024 /* if srcSize < ZSTD_PREDEF_THRESHOLD, symbols' cost is assumed static, directly determined by pre-defined distributions */
Expand All @@ -24,11 +23,11 @@
* Price functions for optimal parser
***************************************/

#if 0 /* approximation at bit level */
#if 0 /* approximation at bit level (for tests) */
# define BITCOST_ACCURACY 0
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define WEIGHT(stat) ((void)opt, ZSTD_bitWeight(stat))
#elif 0 /* fractional bit accuracy */
# define WEIGHT(stat, opt) ((void)opt, ZSTD_bitWeight(stat))
#elif 0 /* fractional bit accuracy (for tests) */
# define BITCOST_ACCURACY 8
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define WEIGHT(stat,opt) ((void)opt, ZSTD_fracWeight(stat))
Expand Down Expand Up @@ -79,25 +78,46 @@ static void ZSTD_setBasePrices(optState_t* optPtr, int optLevel)
}


/* ZSTD_downscaleStat() :
* reduce all elements in table by a factor 2^(ZSTD_FREQ_DIV+malus)
* return the resulting sum of elements */
static U32 ZSTD_downscaleStat(unsigned* table, U32 lastEltIndex, int malus)
static U32 sum_u32(const unsigned table[], size_t nbElts)
{
size_t n;
U32 total = 0;
for (n=0; n<nbElts; n++) {
total += table[n];
}
return total;
}

static U32 ZSTD_downscaleStats(unsigned* table, U32 lastEltIndex, U32 shift)
{
U32 s, sum=0;
DEBUGLOG(5, "ZSTD_downscaleStat (nbElts=%u)", (unsigned)lastEltIndex+1);
assert(ZSTD_FREQ_DIV+malus > 0 && ZSTD_FREQ_DIV+malus < 31);
DEBUGLOG(5, "ZSTD_downscaleStats (nbElts=%u, shift=%u)", (unsigned)lastEltIndex+1, (unsigned)shift);
assert(shift < 30);
for (s=0; s<lastEltIndex+1; s++) {
table[s] = 1 + (table[s] >> (ZSTD_FREQ_DIV+malus));
table[s] = 1 + (table[s] >> shift);
sum += table[s];
}
return sum;
}

/* ZSTD_scaleStats() :
* reduce all elements in table is sum too large
* return the resulting sum of elements */
static U32 ZSTD_scaleStats(unsigned* table, U32 lastEltIndex, U32 logTarget)
{
U32 const prevsum = sum_u32(table, lastEltIndex+1);
U32 const factor = prevsum >> logTarget;
DEBUGLOG(5, "ZSTD_scaleStats (nbElts=%u, target=%u)", (unsigned)lastEltIndex+1, (unsigned)logTarget);
assert(logTarget < 30);
if (factor <= 1) return prevsum;
return ZSTD_downscaleStats(table, lastEltIndex, ZSTD_highbit32(factor));
}

/* ZSTD_rescaleFreqs() :
* if first block (detected by optPtr->litLengthSum == 0) : init statistics
* take hints from dictionary if there is one
* or init from zero, using src for literals stats, or flat 1 for match symbols
* and init from zero if there is none,
* using src for literals stats, and baseline stats for sequence symbols
* otherwise downscale existing stats, to be used as seed for next block.
*/
static void
Expand Down Expand Up @@ -174,36 +194,44 @@ ZSTD_rescaleFreqs(optState_t* const optPtr,
if (compressedLiterals) {
unsigned lit = MaxLit;
HIST_count_simple(optPtr->litFreq, &lit, src, srcSize); /* use raw first block to init statistics */
optPtr->litSum = ZSTD_downscaleStat(optPtr->litFreq, MaxLit, 1);
optPtr->litSum = ZSTD_downscaleStats(optPtr->litFreq, MaxLit, 8);
}

{ unsigned ll;
for (ll=0; ll<=MaxLL; ll++)
optPtr->litLengthFreq[ll] = 1;
{ unsigned const baseLLfreqs[MaxLL+1] = {
4, 2, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1
};
ZSTD_memcpy(optPtr->litLengthFreq, baseLLfreqs, sizeof(baseLLfreqs)); optPtr->litLengthSum = sum_u32(baseLLfreqs, MaxLL+1);
}
optPtr->litLengthSum = MaxLL+1;

{ unsigned ml;
for (ml=0; ml<=MaxML; ml++)
optPtr->matchLengthFreq[ml] = 1;
}
optPtr->matchLengthSum = MaxML+1;

{ unsigned of;
for (of=0; of<=MaxOff; of++)
optPtr->offCodeFreq[of] = 1;
{ unsigned const baseOFCfreqs[MaxOff+1] = {
6, 2, 1, 1, 2, 3, 4, 4,
4, 3, 2, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1
};
Comment on lines +216 to +221
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This is the change that makes the majority of the difference

ZSTD_memcpy(optPtr->offCodeFreq, baseOFCfreqs, sizeof(baseOFCfreqs)); optPtr->offCodeSum = sum_u32(baseOFCfreqs, MaxOff+1);
}
optPtr->offCodeSum = MaxOff+1;


}

} else { /* new block : re-use previous statistics, scaled down */

if (compressedLiterals)
optPtr->litSum = ZSTD_downscaleStat(optPtr->litFreq, MaxLit, 1);
optPtr->litLengthSum = ZSTD_downscaleStat(optPtr->litLengthFreq, MaxLL, 0);
optPtr->matchLengthSum = ZSTD_downscaleStat(optPtr->matchLengthFreq, MaxML, 0);
optPtr->offCodeSum = ZSTD_downscaleStat(optPtr->offCodeFreq, MaxOff, 0);
optPtr->litSum = ZSTD_scaleStats(optPtr->litFreq, MaxLit, 12);
optPtr->litLengthSum = ZSTD_scaleStats(optPtr->litLengthFreq, MaxLL, 11);
optPtr->matchLengthSum = ZSTD_scaleStats(optPtr->matchLengthFreq, MaxML, 11);
optPtr->offCodeSum = ZSTD_scaleStats(optPtr->offCodeFreq, MaxOff, 11);
Comment on lines +231 to +234
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Should the logTarget maybe be based on the block size?

I would expect smaller blocks to want to have a smaller history.

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The update policy could be refined even further. But note that the topic of "block size" has many sub-cases, that probably deserve separate policies.

For example, is the "small block" also the "only block" ?
(I presume that's what you meant.)
In which case, the first pass of btultra2 would produce stats which are already scaled to the size of the block. If there are only a few sequences, then the stats will only contain a few elements, way below the logTarget threshold. In which case, they won't be up-scaled (stats are only down-scaled when they need to). So there is a form of built-in adaptation for small inputs in this process.

But if the "small block" is the N-th block in a long stream, and is also expected to be followed by other blocks of variable size, the situation is different. I would guess that a "stream level" logTarget would feel more appropriate.

This can certainly be analyzed even more.
I believe the update policy is one of these places where some non-negligible gains can still be produced.
And my expectation is that a better update policy should be dynamic, reacting to the "probability" that historic statistics may or may not match the statistics of the following block.

As can be guessed though, this is a fairly complex topic, which would require a dedicated (and time-consuming) study.

}

ZSTD_setBasePrices(optPtr, optLevel);
Expand Down Expand Up @@ -901,11 +929,11 @@ static void ZSTD_optLdm_processMatchCandidate(ZSTD_optLdm_t* optLdm, ZSTD_match_
ZSTD_optLdm_maybeAddMatch(matches, nbMatches, optLdm, currPosInBlock);
}


/*-*******************************
* Optimal parser
*********************************/


static U32 ZSTD_totalLen(ZSTD_optimal_t sol)
{
return sol.litlen + sol.mlen;
Expand Down Expand Up @@ -987,7 +1015,7 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
* in every price. We include the literal length to avoid negative
* prices when we subtract the previous literal length.
*/
opt[0].price = ZSTD_litLengthPrice(litlen, optStatePtr, optLevel);
opt[0].price = (int)ZSTD_litLengthPrice(litlen, optStatePtr, optLevel);

/* large match -> immediate encoding */
{ U32 const maxML = matches[nbMatches-1].len;
Expand All @@ -1007,7 +1035,8 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
} }

/* set prices for first matches starting position == 0 */
{ U32 const literalsPrice = opt[0].price + ZSTD_litLengthPrice(0, optStatePtr, optLevel);
assert(opt[0].price >= 0);
{ U32 const literalsPrice = (U32)opt[0].price + ZSTD_litLengthPrice(0, optStatePtr, optLevel);
U32 pos;
U32 matchNb;
for (pos = 1; pos < minMatch; pos++) {
Expand All @@ -1024,7 +1053,7 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
opt[pos].mlen = pos;
opt[pos].off = offset;
opt[pos].litlen = litlen;
opt[pos].price = sequencePrice;
opt[pos].price = (int)sequencePrice;
} }
last_pos = pos-1;
}
Expand All @@ -1039,9 +1068,9 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
/* Fix current position with one literal if cheaper */
{ U32 const litlen = (opt[cur-1].mlen == 0) ? opt[cur-1].litlen + 1 : 1;
int const price = opt[cur-1].price
+ ZSTD_rawLiteralsCost(ip+cur-1, 1, optStatePtr, optLevel)
+ ZSTD_litLengthPrice(litlen, optStatePtr, optLevel)
- ZSTD_litLengthPrice(litlen-1, optStatePtr, optLevel);
+ (int)ZSTD_rawLiteralsCost(ip+cur-1, 1, optStatePtr, optLevel)
+ (int)ZSTD_litLengthPrice(litlen, optStatePtr, optLevel)
- (int)ZSTD_litLengthPrice(litlen-1, optStatePtr, optLevel);
assert(price < 1000000000); /* overflow check */
if (price <= opt[cur].price) {
DEBUGLOG(7, "cPos:%zi==rPos:%u : better price (%.2f<=%.2f) using literal (ll==%u) (hist:%u,%u,%u)",
Expand Down Expand Up @@ -1084,9 +1113,10 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,
continue; /* skip unpromising positions; about ~+6% speed, -0.01 ratio */
}

assert(opt[cur].price >= 0);
{ U32 const ll0 = (opt[cur].mlen != 0);
U32 const litlen = (opt[cur].mlen == 0) ? opt[cur].litlen : 0;
U32 const previousPrice = opt[cur].price;
U32 const previousPrice = (U32)opt[cur].price;
U32 const basePrice = previousPrice + ZSTD_litLengthPrice(0, optStatePtr, optLevel);
U32 nbMatches = ZSTD_BtGetAllMatches(matches, ms, &nextToUpdate3, inr, iend, dictMode, opt[cur].rep, ll0, minMatch);
U32 matchNb;
Expand Down Expand Up @@ -1126,7 +1156,7 @@ ZSTD_compressBlock_opt_generic(ZSTD_matchState_t* ms,

for (mlen = lastML; mlen >= startML; mlen--) { /* scan downward */
U32 const pos = cur + mlen;
int const price = basePrice + ZSTD_getMatchPrice(offset, mlen, optStatePtr, optLevel);
int const price = (int)basePrice + (int)ZSTD_getMatchPrice(offset, mlen, optStatePtr, optLevel);

if ((pos > last_pos) || (price < opt[pos].price)) {
DEBUGLOG(7, "rPos:%u (ml=%2u) => new better price (%.2f<%.2f)",
Expand Down Expand Up @@ -1222,28 +1252,7 @@ size_t ZSTD_compressBlock_btopt(
}


/* used in 2-pass strategy */
static U32 ZSTD_upscaleStat(unsigned* table, U32 lastEltIndex, int bonus)
{
U32 s, sum=0;
assert(ZSTD_FREQ_DIV+bonus >= 0);
for (s=0; s<lastEltIndex+1; s++) {
table[s] <<= ZSTD_FREQ_DIV+bonus;
table[s]--;
sum += table[s];
}
return sum;
}

/* used in 2-pass strategy */
MEM_STATIC void ZSTD_upscaleStats(optState_t* optPtr)
{
if (ZSTD_compressedLiterals(optPtr))
optPtr->litSum = ZSTD_upscaleStat(optPtr->litFreq, MaxLit, 0);
optPtr->litLengthSum = ZSTD_upscaleStat(optPtr->litLengthFreq, MaxLL, 0);
optPtr->matchLengthSum = ZSTD_upscaleStat(optPtr->matchLengthFreq, MaxML, 0);
optPtr->offCodeSum = ZSTD_upscaleStat(optPtr->offCodeFreq, MaxOff, 0);
}

/* ZSTD_initStats_ultra():
* make a first compression pass, just to seed stats with more accurate starting values.
Expand Down Expand Up @@ -1274,8 +1283,6 @@ ZSTD_initStats_ultra(ZSTD_matchState_t* ms,
ms->window.lowLimit = ms->window.dictLimit;
ms->nextToUpdate = ms->window.dictLimit;

/* re-inforce weight of collected statistics */
ZSTD_upscaleStats(&ms->opt);
}

size_t ZSTD_compressBlock_btultra(
Expand Down
4 changes: 2 additions & 2 deletions lib/dictBuilder/cover.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@
* Console display
***************************************/
#ifndef LOCALDISPLAYLEVEL
static int g_displayLevel = 2;
static int g_displayLevel = 0;
#endif
#undef DISPLAY
#define DISPLAY(...) \
Expand Down Expand Up @@ -735,7 +735,7 @@ ZDICTLIB_API size_t ZDICT_trainFromBuffer_cover(
COVER_map_t activeDmers;
parameters.splitPoint = 1.0;
/* Initialize global data */
g_displayLevel = parameters.zParams.notificationLevel;
g_displayLevel = (int)parameters.zParams.notificationLevel;
/* Checks */
if (!COVER_checkParameters(parameters, dictBufferCapacity)) {
DISPLAYLEVEL(1, "Cover parameters incorrect\n");
Expand Down
8 changes: 4 additions & 4 deletions lib/dictBuilder/fastcover.c
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@
* Console display
***************************************/
#ifndef LOCALDISPLAYLEVEL
static int g_displayLevel = 2;
static int g_displayLevel = 0;
#endif
#undef DISPLAY
#define DISPLAY(...) \
Expand Down Expand Up @@ -549,7 +549,7 @@ ZDICT_trainFromBuffer_fastCover(void* dictBuffer, size_t dictBufferCapacity,
ZDICT_cover_params_t coverParams;
FASTCOVER_accel_t accelParams;
/* Initialize global data */
g_displayLevel = parameters.zParams.notificationLevel;
g_displayLevel = (int)parameters.zParams.notificationLevel;
/* Assign splitPoint and f if not provided */
parameters.splitPoint = 1.0;
parameters.f = parameters.f == 0 ? DEFAULT_F : parameters.f;
Expand Down Expand Up @@ -632,7 +632,7 @@ ZDICT_optimizeTrainFromBuffer_fastCover(
const unsigned accel = parameters->accel == 0 ? DEFAULT_ACCEL : parameters->accel;
const unsigned shrinkDict = 0;
/* Local variables */
const int displayLevel = parameters->zParams.notificationLevel;
const int displayLevel = (int)parameters->zParams.notificationLevel;
unsigned iteration = 1;
unsigned d;
unsigned k;
Expand Down Expand Up @@ -716,7 +716,7 @@ ZDICT_optimizeTrainFromBuffer_fastCover(
data->parameters.splitPoint = splitPoint;
data->parameters.steps = kSteps;
data->parameters.shrinkDict = shrinkDict;
data->parameters.zParams.notificationLevel = g_displayLevel;
data->parameters.zParams.notificationLevel = (unsigned)g_displayLevel;
/* Check the parameters */
if (!FASTCOVER_checkParameters(data->parameters, dictBufferCapacity,
data->ctx->f, accel)) {
Expand Down
25 changes: 16 additions & 9 deletions lib/dictBuilder/zdict.c
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Original file line number Diff line number Diff line change
Expand Up @@ -139,7 +139,7 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
_BitScanForward64( &r, (U64)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctzll((U64)val) >> 3);
return (unsigned)(__builtin_ctzll((U64)val) >> 3);
# else
static const int DeBruijnBytePos[64] = { 0, 0, 0, 0, 0, 1, 1, 2, 0, 3, 1, 3, 1, 4, 2, 7, 0, 2, 3, 6, 1, 5, 3, 5, 1, 3, 4, 4, 2, 5, 6, 7, 7, 0, 1, 2, 3, 3, 4, 6, 2, 6, 5, 5, 3, 4, 5, 6, 7, 1, 2, 4, 6, 4, 4, 5, 7, 2, 6, 5, 7, 6, 7, 7 };
return DeBruijnBytePos[((U64)((val & -(long long)val) * 0x0218A392CDABBD3FULL)) >> 58];
Expand All @@ -150,7 +150,7 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
_BitScanForward( &r, (U32)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctz((U32)val) >> 3);
return (unsigned)(__builtin_ctz((U32)val) >> 3);
# else
static const int DeBruijnBytePos[32] = { 0, 0, 3, 0, 3, 1, 3, 0, 3, 2, 2, 1, 3, 2, 0, 1, 3, 3, 1, 2, 2, 2, 2, 0, 3, 1, 2, 0, 1, 0, 1, 1 };
return DeBruijnBytePos[((U32)((val & -(S32)val) * 0x077CB531U)) >> 27];
Expand All @@ -163,7 +163,7 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
_BitScanReverse64( &r, val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_clzll(val) >> 3);
return (unsigned)(__builtin_clzll(val) >> 3);
# else
unsigned r;
const unsigned n32 = sizeof(size_t)*4; /* calculate this way due to compiler complaining in 32-bits mode */
Expand All @@ -178,7 +178,7 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
_BitScanReverse( &r, (unsigned long)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_clz((U32)val) >> 3);
return (unsigned)(__builtin_clz((U32)val) >> 3);
# else
unsigned r;
if (!(val>>16)) { r=2; val>>=8; } else { r=0; val>>=24; }
Expand Down Expand Up @@ -235,7 +235,7 @@ static dictItem ZDICT_analyzePos(
U32 savings[LLIMIT] = {0};
const BYTE* b = (const BYTE*)buffer;
size_t maxLength = LLIMIT;
size_t pos = suffix[start];
size_t pos = (size_t)suffix[start];
U32 end = start;
dictItem solution;

Expand Down Expand Up @@ -369,7 +369,7 @@ static dictItem ZDICT_analyzePos(
savings[i] = savings[i-1] + (lengthList[i] * (i-3));

DISPLAYLEVEL(4, "Selected dict at position %u, of length %u : saves %u (ratio: %.2f) \n",
(unsigned)pos, (unsigned)maxLength, (unsigned)savings[maxLength], (double)savings[maxLength] / maxLength);
(unsigned)pos, (unsigned)maxLength, (unsigned)savings[maxLength], (double)savings[maxLength] / (double)maxLength);

solution.pos = (U32)pos;
solution.length = (U32)maxLength;
Expand All @@ -379,7 +379,7 @@ static dictItem ZDICT_analyzePos(
{ U32 id;
for (id=start; id<end; id++) {
U32 p, pEnd, length;
U32 const testedPos = suffix[id];
U32 const testedPos = (U32)suffix[id];
if (testedPos == pos)
length = solution.length;
else {
Expand Down Expand Up @@ -442,7 +442,7 @@ static U32 ZDICT_tryMerge(dictItem* table, dictItem elt, U32 eltNbToSkip, const

if ((table[u].pos + table[u].length >= elt.pos) && (table[u].pos < elt.pos)) { /* overlap, existing < new */
/* append */
int const addedLength = (int)eltEnd - (table[u].pos + table[u].length);
int const addedLength = (int)eltEnd - (int)(table[u].pos + table[u].length);
table[u].savings += elt.length / 8; /* rough approx bonus */
if (addedLength > 0) { /* otherwise, elt fully included into existing */
table[u].length += addedLength;
Expand Down Expand Up @@ -766,6 +766,13 @@ static size_t ZDICT_analyzeEntropy(void* dstBuffer, size_t maxDstSize,
pos += fileSizes[u];
}

if (notificationLevel >= 4) {
/* writeStats */
DISPLAYLEVEL(4, "Offset Code Frequencies : \n");
for (u=0; u<=offcodeMax; u++) {
DISPLAYLEVEL(4, "%2u :%7u \n", u, offcodeCount[u]);
} }

/* analyze, build stats, starting with literals */
{ size_t maxNbBits = HUF_buildCTable (hufTable, countLit, 255, huffLog);
if (HUF_isError(maxNbBits)) {
Expand Down Expand Up @@ -872,7 +879,7 @@ static size_t ZDICT_analyzeEntropy(void* dstBuffer, size_t maxDstSize,
MEM_writeLE32(dstPtr+8, bestRepOffset[2].offset);
#else
/* at this stage, we don't use the result of "most common first offset",
as the impact of statistics is not properly evaluated */
* as the impact of statistics is not properly evaluated */
MEM_writeLE32(dstPtr+0, repStartValue[0]);
MEM_writeLE32(dstPtr+4, repStartValue[1]);
MEM_writeLE32(dstPtr+8, repStartValue[2]);
Expand Down
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