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Merge pull request #561 from iburinoc/fsefix

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Fix bug in FSE distribution normalization
This commit is contained in:
Yann Collet 2017-02-22 15:32:22 -08:00 committed by GitHub
commit a395fdbaf0
1 changed files with 12 additions and 3 deletions
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15
lib/compress/fse_compress.c
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@ -506,6 +506,7 @@ unsigned FSE_optimalTableLog(unsigned maxTableLog, size_t srcSize, unsigned maxS
static size_t FSE_normalizeM2(short* norm, U32 tableLog, const unsigned* count, size_t total, U32 maxSymbolValue)
{
short const NOT_YET_ASSIGNED = -2;
U32 s;
U32 distributed = 0;
U32 ToDistribute;
@ -531,7 +532,8 @@ static size_t FSE_normalizeM2(short* norm, U32 tableLog, const unsigned* count,
total -= count[s];
continue;
}
norm[s]=-2;
norm[s]=NOT_YET_ASSIGNED;
}
ToDistribute = (1 << tableLog) - distributed;
@ -539,7 +541,7 @@ static size_t FSE_normalizeM2(short* norm, U32 tableLog, const unsigned* count,
/* risk of rounding to zero */
lowOne = (U32)((total * 3) / (ToDistribute * 2));
for (s=0; s<=maxSymbolValue; s++) {
if ((norm[s] == -2) && (count[s] <= lowOne)) {
if ((norm[s] == NOT_YET_ASSIGNED) && (count[s] <= lowOne)) {
norm[s] = 1;
distributed++;
total -= count[s];
@ -559,12 +561,19 @@ static size_t FSE_normalizeM2(short* norm, U32 tableLog, const unsigned* count,
return 0;
}
if (total == 0) {
/* all of the symbols were low enough for the lowOne or lowThreshold */
for (s=0; ToDistribute > 0; s = (s+1)%(maxSymbolValue+1))
if (norm[s] > 0) ToDistribute--, norm[s]++;
return 0;
}
{ U64 const vStepLog = 62 - tableLog;
U64 const mid = (1ULL << (vStepLog-1)) - 1;
U64 const rStep = ((((U64)1<<vStepLog) * ToDistribute) + mid) / total; /* scale on remaining */
U64 tmpTotal = mid;
for (s=0; s<=maxSymbolValue; s++) {
if (norm[s]==-2) {
if (norm[s]==NOT_YET_ASSIGNED) {
U64 const end = tmpTotal + (count[s] * rStep);
U32 const sStart = (U32)(tmpTotal >> vStepLog);
U32 const sEnd = (U32)(end >> vStepLog);