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implemented fractional bit cost evaluation

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for FSE symbols.

While it seems to work, the gains are negligible compared to rough maxNbBits evaluation.
There are even a few losses sometimes, that still need to be explained.
Furthermode, there are still cases where btlazy2 does a better job than btopt,
which seems rather strange too.
This commit is contained in:
Yann Collet
2018-05-08 17:43:13 -07:00
parent 1aff63b114
commit ba2ad9b6b9
3 changed files with 24 additions and 8 deletions
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lib/compress/zstd_opt.c
+9 -6
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@@ -126,11 +126,13 @@ 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);
return (LL_bits[llCode] + FSE_getMaxNbBits(cstate.symbolTT, llCode)) << 8;
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);
return price;
}
if (optPtr->priceType == zop_predef) return ZSTD_highbit32((U32)litLength+1);
/* literal Length */
/* dynamic statistics */
{ U32 const llCode = ZSTD_LLcode(litLength);
return (LL_bits[llCode] + optPtr->log2litLengthSum - ZSTD_highbit32(optPtr->litLengthFreq[llCode]+1)) << 8;
}
@@ -156,7 +158,9 @@ 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] + FSE_getMaxNbBits(cstate.symbolTT, llCode)) - FSE_getMaxNbBits(cstate.symbolTT, 0)) * 256;
return (int)(LL_bits[llCode] * 256)
+ FSE_bitCost_b256(cstate.symbolTT, cstate.stateLog, llCode)
- FSE_bitCost_b256(cstate.symbolTT, cstate.stateLog, 0);
}
if (optPtr->priceType >= zop_predef) return ZSTD_highbit32(litLength+1);
@@ -205,9 +209,8 @@ 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_getMaxNbBits(offstate.symbolTT, offCode) + offCode
+ FSE_getMaxNbBits(mlstate.symbolTT, mlCode) + ML_bits[mlCode])
* 256;
return FSE_bitCost_b256(offstate.symbolTT, offstate.stateLog, offCode) + offCode*256
+ FSE_bitCost_b256(mlstate.symbolTT, mlstate.stateLog, mlCode) + ML_bits[mlCode]*256;
}
if (optPtr->priceType == zop_predef) /* fixed scheme, do not use statistics */