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faster decoding in 32-bits mode for long offsets (tentative)

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On my laptop:
Before:
./zstd32 -b --zstd=wlog=27 silesia.tar enwik8 -S
 3#silesia.tar       : 211984896 ->  66683478 (3.179),  97.6 MB/s , 400.7 MB/s
 3#enwik8            : 100000000 ->  35643153 (2.806),  76.5 MB/s , 303.2 MB/s

After:
./zstd32 -b --zstd=wlog=27 silesia.tar enwik8 -S
 3#silesia.tar       : 211984896 ->  66683478 (3.179),  97.4 MB/s , 435.0 MB/s
 3#enwik8            : 100000000 ->  35643153 (2.806),  76.2 MB/s , 338.1 MB/s

Mileage vary, depending on file, and cpu type.
But a generic rule is : x86 benefits less from "long-offset mode" than x64,
maybe due to register pressure.
On "entropy", long-mode is _never_ a win for x86.
On my laptop though, it may, depending on file and compression level
(enwik8 benefits more from "long-mode" than silesia).
This commit is contained in:
Yann Collet 2018-02-03 23:54:10 -08:00
parent 1291d9d7cf
commit 94efb1749d
1 changed files with 23 additions and 20 deletions
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43
lib/decompress/zstd_decompress.c
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@ -23,7 +23,7 @@
/*!
* LEGACY_SUPPORT :
* if set to 1, ZSTD_decompress() can decode older formats (v0.1+)
* if set to 1+, ZSTD_decompress() can decode older formats (v0.1+)
*/
#ifndef ZSTD_LEGACY_SUPPORT
# define ZSTD_LEGACY_SUPPORT 0
@ -235,8 +235,8 @@ void ZSTD_copyDCtx(ZSTD_DCtx* dstDCtx, const ZSTD_DCtx* srcDCtx)
/*-*************************************************************
* Decompression section
***************************************************************/
* Frame header decoding
***************************************************************/
/*! ZSTD_isFrame() :
* Tells if the content of `buffer` starts with a valid Frame Identifier.
@ -258,7 +258,7 @@ unsigned ZSTD_isFrame(const void* buffer, size_t size)
/** ZSTD_frameHeaderSize_internal() :
* srcSize must be large enough to reach header size fields.
* note : only works for formats ZSTD_f_zstd1 and ZSTD_f_zstd1_magicless
* note : only works for formats ZSTD_f_zstd1 and ZSTD_f_zstd1_magicless.
* @return : size of the Frame Header
* or an error code, which can be tested with ZSTD_isError() */
static size_t ZSTD_frameHeaderSize_internal(const void* src, size_t srcSize, ZSTD_format_e format)
@ -481,6 +481,10 @@ static size_t ZSTD_decodeFrameHeader(ZSTD_DCtx* dctx, const void* src, size_t he
}
/*-*************************************************************
* Block decoding
***************************************************************/
/*! ZSTD_getcBlockSize() :
* Provides the size of compressed block from block header `src` */
size_t ZSTD_getcBlockSize(const void* src, size_t srcSize,
@ -936,13 +940,14 @@ static seq_t ZSTD_decodeSequence(seqState_t* seqState, const ZSTD_longOffset_e l
ZSTD_STATIC_ASSERT(ZSTD_lo_isLongOffset == 1);
ZSTD_STATIC_ASSERT(LONG_OFFSETS_MAX_EXTRA_BITS_32 == 5);
assert(ofBits <= MaxOff);
if (MEM_32bits() && longOffsets) {
U32 const extraBits = ofBits - MIN(ofBits, STREAM_ACCUMULATOR_MIN_32-1);
if (MEM_32bits() && longOffsets && (ofBits >= STREAM_ACCUMULATOR_MIN_32)) {
U32 const extraBits = ofBits - MIN(ofBits, 32 - seqState->DStream.bitsConsumed);
offset = OF_base[ofCode] + (BIT_readBitsFast(&seqState->DStream, ofBits - extraBits) << extraBits);
if (MEM_32bits() || extraBits) BIT_reloadDStream(&seqState->DStream);
BIT_reloadDStream(&seqState->DStream);
if (extraBits) offset += BIT_readBitsFast(&seqState->DStream, extraBits);
assert(extraBits <= LONG_OFFSETS_MAX_EXTRA_BITS_32); /* to avoid another reload */
} else {
offset = OF_base[ofCode] + BIT_readBitsFast(&seqState->DStream, ofBits); /* <= (ZSTD_WINDOWLOG_MAX-1) bits */
offset = OF_base[ofCode] + BIT_readBitsFast(&seqState->DStream, ofBits/*>0*/); /* <= (ZSTD_WINDOWLOG_MAX-1) bits */
if (MEM_32bits()) BIT_reloadDStream(&seqState->DStream);
}
}
@ -955,7 +960,7 @@ static seq_t ZSTD_decodeSequence(seqState_t* seqState, const ZSTD_longOffset_e l
if (offset != 1) seqState->prevOffset[2] = seqState->prevOffset[1];
seqState->prevOffset[1] = seqState->prevOffset[0];
seqState->prevOffset[0] = offset = temp;
} else {
} else { /* offset == 0 */
offset = seqState->prevOffset[0];
}
} else {
@ -967,16 +972,16 @@ static seq_t ZSTD_decodeSequence(seqState_t* seqState, const ZSTD_longOffset_e l
}
seq.matchLength = ML_base[mlCode]
+ ((mlCode>31) ? BIT_readBitsFast(&seqState->DStream, mlBits) : 0); /* <= 16 bits */
+ ((mlCode>31) ? BIT_readBitsFast(&seqState->DStream, mlBits/*>0*/) : 0); /* <= 16 bits */
if (MEM_32bits() && (mlBits+llBits >= STREAM_ACCUMULATOR_MIN_32-LONG_OFFSETS_MAX_EXTRA_BITS_32))
BIT_reloadDStream(&seqState->DStream);
if (MEM_64bits() && (totalBits >= STREAM_ACCUMULATOR_MIN_64-(LLFSELog+MLFSELog+OffFSELog)))
BIT_reloadDStream(&seqState->DStream);
/* Verify that there is enough bits to read the rest of the data in 64-bit mode. */
/* Ensure there are enough bits to read the rest of data in 64-bit mode. */
ZSTD_STATIC_ASSERT(16+LLFSELog+MLFSELog+OffFSELog < STREAM_ACCUMULATOR_MIN_64);
seq.litLength = LL_base[llCode]
+ ((llCode>15) ? BIT_readBitsFast(&seqState->DStream, llBits) : 0); /* <= 16 bits */
+ ((llCode>15) ? BIT_readBitsFast(&seqState->DStream, llBits/*>0*/) : 0); /* <= 16 bits */
if (MEM_32bits())
BIT_reloadDStream(&seqState->DStream);
@ -1364,13 +1369,13 @@ static size_t ZSTD_decompressSequencesLong(
FSE_initDState(&seqState.stateML, &seqState.DStream, dctx->MLTptr);
/* prepare in advance */
for (seqNb=0; (BIT_reloadDStream(&seqState.DStream) <= BIT_DStream_completed) && seqNb<seqAdvance; seqNb++) {
for (seqNb=0; (BIT_reloadDStream(&seqState.DStream) <= BIT_DStream_completed) && (seqNb<seqAdvance); seqNb++) {
sequences[seqNb] = ZSTD_decodeSequenceLong(&seqState, isLongOffset);
}
if (seqNb<seqAdvance) return ERROR(corruption_detected);
/* decode and decompress */
for ( ; (BIT_reloadDStream(&(seqState.DStream)) <= BIT_DStream_completed) && seqNb<nbSeq ; seqNb++) {
for ( ; (BIT_reloadDStream(&(seqState.DStream)) <= BIT_DStream_completed) && (seqNb<nbSeq) ; seqNb++) {
seq_t const sequence = ZSTD_decodeSequenceLong(&seqState, isLongOffset);
size_t const oneSeqSize = ZSTD_execSequenceLong(op, oend, sequences[(seqNb-ADVANCED_SEQS) & STOSEQ_MASK], &litPtr, litEnd, prefixStart, dictStart, dictEnd);
if (ZSTD_isError(oneSeqSize)) return oneSeqSize;
@ -1411,13 +1416,9 @@ static size_t ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx,
/* isLongOffset must be true if there are long offsets.
* Offsets are long if they are larger than 2^STREAM_ACCUMULATOR_MIN.
* We don't expect that to be the case in 64-bit mode.
* If we are in block mode we don't know the window size, so we have to be
* conservative.
* In block mode, window size is not known, so we have to be conservative. (note: but it could be evaluated from current-lowLimit)
*/
ZSTD_longOffset_e const isLongOffset = (ZSTD_longOffset_e)(MEM_32bits() && (!frame || dctx->fParams.windowSize > (1ULL << STREAM_ACCUMULATOR_MIN)));
/* windowSize could be any value at this point, since it is only validated
* in the streaming API.
*/
DEBUGLOG(5, "ZSTD_decompressBlock_internal (size : %u)", (U32)srcSize);
if (srcSize >= ZSTD_BLOCKSIZE_MAX) return ERROR(srcSize_wrong);
@ -1429,7 +1430,9 @@ static size_t ZSTD_decompressBlock_internal(ZSTD_DCtx* dctx,
ip += litCSize;
srcSize -= litCSize;
}
if (frame && dctx->fParams.windowSize > (1<<23))
if ( frame /* windowSize exists */
&& (dctx->fParams.windowSize > (1<<24))
&& MEM_64bits() /* x86 benefits less from long mode than x64 */ )
return ZSTD_decompressSequencesLong(dctx, dst, dstCapacity, ip, srcSize, isLongOffset);
return ZSTD_decompressSequences(dctx, dst, dstCapacity, ip, srcSize, isLongOffset);
}