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zstd_opt: added comments, as requested by @terrelln

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This commit is contained in:
Yann Collet 2017-11-29 15:19:00 -08:00
parent bc42bc3b1d
commit f98ee994c4
1 changed files with 23 additions and 15 deletions
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38
lib/compress/zstd_opt.c
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@ -89,6 +89,9 @@ static void ZSTD_rescaleFreqs(optState_t* const optPtr,
}
/* ZSTD_rawLiteralsCost() :
* cost of literals (only) in given segment (which length can be null)
* does not include cost of literalLength symbol */
static U32 ZSTD_rawLiteralsCost(const BYTE* const literals, U32 const litLength,
const optState_t* const optPtr)
{
@ -104,6 +107,8 @@ static U32 ZSTD_rawLiteralsCost(const BYTE* const literals, U32 const litLength,
}
}
/* ZSTD_litLengthPrice() :
* cost of literalLength symbol */
static U32 ZSTD_litLengthPrice(U32 const litLength, const optState_t* const optPtr)
{
if (optPtr->staticPrices) return ZSTD_highbit32((U32)litLength+1);
@ -115,6 +120,9 @@ static U32 ZSTD_litLengthPrice(U32 const litLength, const optState_t* const optP
}
}
/* ZSTD_litLengthPrice() :
* cost of the literal part of a sequence,
* including literals themselves, and literalLength symbol */
static U32 ZSTD_fullLiteralsCost(const BYTE* const literals, U32 const litLength,
const optState_t* const optPtr)
{
@ -122,6 +130,10 @@ static U32 ZSTD_fullLiteralsCost(const BYTE* const literals, U32 const litLength
+ ZSTD_litLengthPrice(litLength, optPtr);
}
/* ZSTD_litLengthContribution() :
* @return ( cost(litlength) - cost(0) )
* this value can then be added to rawLiteralsCost()
* to provide a cost which is directly comparable to a match ending at same position */
static int ZSTD_litLengthContribution(U32 const litLength, const optState_t* const optPtr)
{
if (optPtr->staticPrices) return ZSTD_highbit32(litLength+1);
@ -139,6 +151,10 @@ static int ZSTD_litLengthContribution(U32 const litLength, const optState_t* con
}
}
/* ZSTD_literalsContribution() :
* creates a fake cost for the literals part of a sequence
* which can be compared to the ending cost of a match
* should a new match start at this position */
static int ZSTD_literalsContribution(const BYTE* const literals, U32 const litLength,
const optState_t* const optPtr)
{
@ -147,8 +163,9 @@ static int ZSTD_literalsContribution(const BYTE* const literals, U32 const litLe
return contribution;
}
/* ZSTD_getMatchPrice() :
* Provides the cost of the match part (offset + matchLength) of a sequence
* Must be combined with ZSTD_fullLiteralsCost() to get the full cost of a sequence.
* optLevel: when <2, favors small offset for decompression speed (improved cache efficiency) */
FORCE_INLINE_TEMPLATE U32 ZSTD_getMatchPrice(
U32 const offset, U32 const matchLength,
@ -171,14 +188,13 @@ FORCE_INLINE_TEMPLATE U32 ZSTD_getMatchPrice(
price += ML_bits[mlCode] + optPtr->log2matchLengthSum - ZSTD_highbit32(optPtr->matchLengthFreq[mlCode]+1);
}
//price += optPtr->factor;
DEBUGLOG(8, "ZSTD_getMatchPrice(ml:%u) = %u", matchLength, price);
return price;
}
static void ZSTD_updateStats(optState_t* const optPtr,
U32 litLength, const BYTE* literals,
U32 offsetCode, U32 matchLength)
U32 litLength, const BYTE* literals,
U32 offsetCode, U32 matchLength)
{
/* literals */
{ U32 u;
@ -209,7 +225,9 @@ static void ZSTD_updateStats(optState_t* const optPtr,
}
/* function safe only for comparisons */
/* ZSTD_readMINMATCH() :
* function safe only for comparisons
* assumption : memPtr must be at least 4 bytes before end of buffer */
MEM_STATIC U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
{
switch (length)
@ -454,16 +472,6 @@ repcodes_t ZSTD_updateRep(U32 const rep[3], U32 const offset, U32 const ll0)
return newReps;
}
/* update opt[pos] and last_pos */
#define SET_PRICE(pos, mlen_, offset_, litlen_, price_, rep_) \
{ \
while (last_pos < pos) { opt[last_pos+1].price = ZSTD_MAX_PRICE; last_pos++; } \
opt[pos].mlen = mlen_; \
opt[pos].off = offset_; \
opt[pos].litlen = litlen_; \
opt[pos].price = price_; \
memcpy(opt[pos].rep, &rep_, sizeof(rep_)); \
}
typedef struct {
const BYTE* anchor;