AuroraMiddleware/zstd
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

switchable bit-approximation / fractional-bit accuracy modes

Browse Source 
also : makes it possible to select nb of fractional bits.
This commit is contained in:
Yann Collet 2018-05-09 10:48:09 -07:00
parent ba2ad9b6b9
commit c0da0f5e9e
2 changed files with 37 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
lib/common/fse.h
View File

@ -582,16 +582,20 @@ MEM_STATIC U32 FSE_getMaxNbBits(const FSE_symbolCompressionTransform* symbolTT,
/* FSE_bitCost_b256() :
* Approximate symbol cost,
* provide fractional value, using fixed-point format (8 bit) */
MEM_STATIC U32 FSE_bitCost_b256(const FSE_symbolCompressionTransform* symbolTT, U32 tableLog, U32 symbolValue)
* provide fractional value, using fixed-point format (accuracyLog fractional bits) */
MEM_STATIC U32 FSE_bitCost(const FSE_symbolCompressionTransform* symbolTT, U32 tableLog, U32 symbolValue, U32 accuracyLog)
{
U32 const minNbBits = symbolTT[symbolValue].deltaNbBits >> 16;
U32 const threshold = (minNbBits+1) << 16;
assert(symbolTT[symbolValue].deltaNbBits + (1<<tableLog) <= threshold);
U32 const deltaFromThreshold = threshold - (symbolTT[symbolValue].deltaNbBits + (1 << tableLog));
U32 const normalizedDeltaFromThreshold = (deltaFromThreshold << 8) >> tableLog; /* linear interpolation (very approximate) */
assert(normalizedDeltaFromThreshold <= 256);
return (minNbBits+1)*256 - normalizedDeltaFromThreshold;
assert(tableLog < 16);
U32 const tableSize = 1 << tableLog;
assert(symbolTT[symbolValue].deltaNbBits + tableSize <= threshold);
U32 const deltaFromThreshold = threshold - (symbolTT[symbolValue].deltaNbBits + tableSize);
assert(accuracyLog < 31-tableLog); /* ensure enough room for renormalization double shift */
U32 const normalizedDeltaFromThreshold = (deltaFromThreshold << accuracyLog) >> tableLog; /* linear interpolation (very approximate) */
U32 const bitMultiplier = 1 << accuracyLog;
assert(normalizedDeltaFromThreshold <= bitMultiplier);
return (minNbBits+1)*bitMultiplier - normalizedDeltaFromThreshold;
}

42
lib/compress/zstd_opt.c
View File

@ -91,6 +91,15 @@ static void ZSTD_rescaleFreqs(optState_t* const optPtr,
ZSTD_setLog2Prices(optPtr);
}
#if 1 /* approximation at bit level */
# define BITCOST_ACCURACY 0
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define BITCOST_SYMBOL(t,l,s) ((void)l, FSE_getMaxNbBits(t,s)*BITCOST_MULTIPLIER)
#else /* fractional bit accuracy */
# define BITCOST_ACCURACY 8
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define BITCOST_SYMBOL(t,l,s) FSE_bitCost(t,l,s,BITCOST_ACCURACY)
#endif
/* ZSTD_rawLiteralsCost() :
* cost of literals (only) in specified segment (which length can be 0).
@ -98,23 +107,23 @@ static void ZSTD_rescaleFreqs(optState_t* const optPtr,
static U32 ZSTD_rawLiteralsCost(const BYTE* const literals, U32 const litLength,
const optState_t* const optPtr)
{
if (litLength == 0) return 0;
if (optPtr->priceType == zop_predef) return (litLength*6); /* 6 bit per literal - no statistic used */
if (optPtr->priceType == zop_static) {
U32 u, cost;
assert(optPtr->symbolCosts != NULL);
assert(optPtr->symbolCosts->hufCTable_repeatMode == HUF_repeat_valid);
for (u=0, cost=0; u < litLength; u++)
cost += HUF_getNbBits(optPtr->symbolCosts->hufCTable, literals[u]);
return cost << 8;
return cost * BITCOST_MULTIPLIER;
}
if (optPtr->priceType == zop_predef) return (litLength*6); /* 6 bit per literal - no statistic used */
if (litLength == 0) return 0;
/* literals */
/* dynamic statistics */
{ U32 u;
U32 cost = litLength * optPtr->log2litSum;
for (u=0; u < litLength; u++)
cost -= ZSTD_highbit32(optPtr->litFreq[literals[u]]+1);
return cost << 8;
return cost * BITCOST_MULTIPLIER;
}
}
@ -126,15 +135,15 @@ static U32 ZSTD_litLengthPrice(U32 const litLength, const optState_t* const optP
U32 const llCode = ZSTD_LLcode(litLength);
FSE_CState_t cstate;
FSE_initCState(&cstate, optPtr->symbolCosts->litlengthCTable);
U32 const price = LL_bits[llCode]*256 + FSE_bitCost_b256(cstate.symbolTT, cstate.stateLog, llCode);
DEBUGLOG(8, "ZSTD_litLengthPrice: ll=%u, bitCost=%.2f", litLength, (double)price / 256);
U32 const price = LL_bits[llCode]*BITCOST_MULTIPLIER + BITCOST_SYMBOL(cstate.symbolTT, cstate.stateLog, llCode);
DEBUGLOG(8, "ZSTD_litLengthPrice: ll=%u, bitCost=%.2f", litLength, (double)price / BITCOST_MULTIPLIER);
return price;
}
if (optPtr->priceType == zop_predef) return ZSTD_highbit32((U32)litLength+1);
/* dynamic statistics */
{ U32 const llCode = ZSTD_LLcode(litLength);
return (LL_bits[llCode] + optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1)) << 8;
return (LL_bits[llCode] + optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1)) * BITCOST_MULTIPLIER;
}
}
@ -158,18 +167,18 @@ static int ZSTD_litLengthContribution(U32 const litLength, const optState_t* con
U32 const llCode = ZSTD_LLcode(litLength);
FSE_CState_t cstate;
FSE_initCState(&cstate, optPtr->symbolCosts->litlengthCTable);
return (int)(LL_bits[llCode] * 256)
+ FSE_bitCost_b256(cstate.symbolTT, cstate.stateLog, llCode)
- FSE_bitCost_b256(cstate.symbolTT, cstate.stateLog, 0);
return (int)(LL_bits[llCode] * BITCOST_MULTIPLIER)
+ BITCOST_SYMBOL(cstate.symbolTT, cstate.stateLog, llCode)
- BITCOST_SYMBOL(cstate.symbolTT, cstate.stateLog, 0);
}
if (optPtr->priceType >= zop_predef) return ZSTD_highbit32(litLength+1);
/* literal Length */
/* dynamic statistics */
{ U32 const llCode = ZSTD_LLcode(litLength);
int const contribution = (LL_bits[llCode]
+ ZSTD_highbit32(optPtr->litLengthFreq[0]+1)
- ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1))
* 256;
* BITCOST_MULTIPLIER;
#if 1
return contribution;
#else
@ -209,13 +218,14 @@ ZSTD_getMatchPrice(U32 const offset, U32 const matchLength,
FSE_CState_t mlstate, offstate;
FSE_initCState(&mlstate, optPtr->symbolCosts->matchlengthCTable);
FSE_initCState(&offstate, optPtr->symbolCosts->offcodeCTable);
return FSE_bitCost_b256(offstate.symbolTT, offstate.stateLog, offCode) + offCode*256
+ FSE_bitCost_b256(mlstate.symbolTT, mlstate.stateLog, mlCode) + ML_bits[mlCode]*256;
return BITCOST_SYMBOL(offstate.symbolTT, offstate.stateLog, offCode) + offCode*BITCOST_MULTIPLIER
+ BITCOST_SYMBOL(mlstate.symbolTT, mlstate.stateLog, mlCode) + ML_bits[mlCode]*BITCOST_MULTIPLIER;
}
if (optPtr->priceType == zop_predef) /* fixed scheme, do not use statistics */
return ZSTD_highbit32(mlBase+1) + 16 + offCode;
/* dynamic statistics */
price = offCode + optPtr->log2offCodeSum - ZSTD_highbit32(optPtr->offCodeFreq[offCode]+1);
if ((optLevel<2) /*static*/ && offCode >= 20) price += (offCode-19)*2; /* handicap for long distance offsets, favor decompression speed */
@ -225,7 +235,7 @@ ZSTD_getMatchPrice(U32 const offset, U32 const matchLength,
}
DEBUGLOG(8, "ZSTD_getMatchPrice(ml:%u) = %u", matchLength, price);
return price << 8;
return price * BITCOST_MULTIPLIER;
}
static void ZSTD_updateStats(optState_t* const optPtr,