Initial Pipelined Implementation for ZSTD_fast
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W. Felix Handte
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80bc12b33a
@ -183,6 +183,255 @@ _match: /* Requires: ip0, match0, offcode */
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}
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/**
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* If you squint hard enough (and ignore repcodes), the search operation at any
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* given position is broken into 4 stages:
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*
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* 1. Hash (map position to hash value via input read)
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* 2. Lookup (map hash val to index via hashtable read)
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* 3. Load (map index to value at that position via input read)
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* 4. Compare
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*
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* Each of these steps involves a memory read at an address which is computed
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* from the previous step. This means these steps must be sequenced and their
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* latencies are cumulative.
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*
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* Rather than do 1->2->3->4 sequentially for a single position before moving
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* onto the next, this implementation interleaves these operations across the
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* next few positions:
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*
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* Pos | Time -->
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* ----+-------------------
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* N | ...4
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* N+1 | ... 3 4
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* N+2 | ... 2 3 4
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* N+3 | 1 2 3
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* N+4 | 1 2
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* N+5 | 1
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*
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* This is very much analogous to the pipelining of execution in a CPU. And just
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* like a CPU, we have to dump the pipeline when we find a match (i.e., take a
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* branch).
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*
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* When this happens, we throw away our current state, and do the following prep
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* to re-enter the loop:
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*
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* Pos | Time -->
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* ----+-------------------
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* N | 1 2 3
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* N+1 | 1 2
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* N+2 | 1
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*
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* This is also the work we do at the beginning to enter the loop initially.
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*/
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FORCE_INLINE_TEMPLATE size_t
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ZSTD_compressBlock_fast_generic_pipelined(
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ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
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void const* src, size_t srcSize,
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U32 const mls)
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{
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const ZSTD_compressionParameters* const cParams = &ms->cParams;
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U32* const hashTable = ms->hashTable;
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U32 const hlog = cParams->hashLog;
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/* support stepSize of 0 */
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size_t const stepSize = cParams->targetLength + !(cParams->targetLength);
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const BYTE* const base = ms->window.base;
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const BYTE* const istart = (const BYTE*)src;
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const U32 endIndex = (U32)((size_t)(istart - base) + srcSize);
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const U32 prefixStartIndex = ZSTD_getLowestPrefixIndex(ms, endIndex, cParams->windowLog);
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const BYTE* const prefixStart = base + prefixStartIndex;
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const BYTE* const iend = istart + srcSize;
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const BYTE* const ilimit = iend - HASH_READ_SIZE;
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const BYTE* anchor = istart;
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const BYTE* ip0 = istart;
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const BYTE* ip1;
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const BYTE* ip2;
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const BYTE* ip3;
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U32 current0;
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U32 rep_offset1 = rep[0];
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U32 rep_offset2 = rep[1];
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U32 offsetSaved = 0;
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size_t hash0; /* hash for ip0 */
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size_t hash1; /* hash for ip1 */
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size_t hash2; /* hash for ip2 */
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size_t hash3; /* hash for ip3 */
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U32 idx0; /* match idx for ip0 */
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U32 idx1; /* match idx for ip1 */
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U32 idx2; /* match idx for ip2 */
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U32 mval; /* src value at match idx */
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U32 rval; /* src value at ip2 - repcode */
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U32 offcode;
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const BYTE* match0;
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size_t mLength;
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DEBUGLOG(5, "ZSTD_compressBlock_fast_generic_pipelined");
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ip0 += (ip0 == prefixStart);
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{ U32 const curr = (U32)(ip0 - base);
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U32 const windowLow = ZSTD_getLowestPrefixIndex(ms, curr, cParams->windowLog);
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U32 const maxRep = curr - windowLow;
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if (rep_offset2 > maxRep) offsetSaved = rep_offset2, rep_offset2 = 0;
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if (rep_offset1 > maxRep) offsetSaved = rep_offset1, rep_offset1 = 0;
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}
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/* start each op */
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_start: /* Requires: ip0 */
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/* calculate positions, ip0 - anchor == 0, so we skip step calc */
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ip1 = ip0 + stepSize;
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ip2 = ip1 + stepSize;
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ip3 = ip2 + stepSize;
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if (ip3 >= ilimit) {
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goto _cleanup;
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}
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hash0 = ZSTD_hashPtr(ip0, hlog, mls);
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hash1 = ZSTD_hashPtr(ip1, hlog, mls);
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hash2 = ZSTD_hashPtr(ip2, hlog, mls);
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idx0 = hashTable[hash0];
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idx1 = hashTable[hash1];
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if (idx0 >= prefixStartIndex) {
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mval = MEM_read32(base + idx0);
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} else {
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mval = MEM_read32(ip0) ^ 1;
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}
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rval = MEM_read32(ip2 - rep_offset1);
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do {
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current0 = ip0 - base;
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// DEBUGLOG(5, "Searching ip0 = %u", (U32)(ip0 - istart));
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/* write back hash table entry */
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hashTable[hash0] = current0;
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/* check repcode at ip[2] */
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if ((MEM_read32(ip2) == rval) & (rep_offset1 > 0)) {
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ip0 = ip2;
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match0 = ip0 - rep_offset1;
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mLength = ip0[-1] == match0[-1];
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ip0 -= mLength;
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match0 -= mLength;
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offcode = 0;
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mLength += 4;
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goto _match;
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}
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/* check match at ip[0] */
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if (MEM_read32(ip0) == mval) {
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/* found a match! */
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goto _offset;
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}
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/* load next rval */
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rval = MEM_read32(ip3 - rep_offset1);
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/* load match for ip[1] */
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if (idx1 >= prefixStartIndex) {
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mval = MEM_read32(base + idx1);
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} else {
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mval = MEM_read32(ip1) ^ 1; /* guaranteed to not match. */
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}
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/* lookup ip[2] */
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idx2 = hashTable[hash2];
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/* hash ip[3] */
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hash3 = ZSTD_hashPtr(ip3, hlog, mls);
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/* advance to next positions */
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{
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size_t const step = ((size_t)(ip2 - anchor) >> (kSearchStrength - 1)) + stepSize;
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assert(step >= 1);
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idx0 = idx1;
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idx1 = idx2;
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hash0 = hash1;
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hash1 = hash2;
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hash2 = hash3;
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ip0 = ip1;
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ip1 = ip2;
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ip2 = ip3;
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ip3 = ip3 + step;
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}
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} while (ip3 < ilimit);
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_cleanup:
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/* Find matches at end of block. */
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/* TODO */
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/* save reps for next block */
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rep[0] = rep_offset1 ? rep_offset1 : offsetSaved;
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rep[1] = rep_offset2 ? rep_offset2 : offsetSaved;
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/* Return the last literals size */
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return (size_t)(iend - anchor);
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_offset: /* Requires: ip0, idx0 */
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/* Compute the offset code. */
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match0 = base + idx0;
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rep_offset2 = rep_offset1;
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rep_offset1 = (U32)(ip0-match0);
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offcode = rep_offset1 + ZSTD_REP_MOVE;
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mLength = 4;
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/* Count the backwards match length. */
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while (((ip0>anchor) & (match0>prefixStart)) && (ip0[-1] == match0[-1])) {
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ip0--;
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match0--;
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mLength++;
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}
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_match: /* Requires: ip0, match0, offcode */
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/* Count the forward length. */
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mLength += ZSTD_count(ip0 + mLength, match0 + mLength, iend);
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ZSTD_storeSeq(seqStore, (size_t)(ip0 - anchor), anchor, iend, offcode, mLength - MINMATCH);
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ip0 += mLength;
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anchor = ip0;
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/* write next hash table entry */
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if (ip1 < ip0) {
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hashTable[hash1] = ip1 - base;
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}
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/* Fill table and check for immediate repcode. */
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if (ip0 <= ilimit) {
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/* Fill Table */
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assert(base+current0+2 > istart); /* check base overflow */
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hashTable[ZSTD_hashPtr(base+current0+2, hlog, mls)] = current0+2; /* here because current+2 could be > iend-8 */
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hashTable[ZSTD_hashPtr(ip0-2, hlog, mls)] = (U32)(ip0-2-base);
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if (rep_offset2 > 0) { /* rep_offset2==0 means rep_offset2 is invalidated */
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while ( (ip0 <= ilimit) && (MEM_read32(ip0) == MEM_read32(ip0 - rep_offset2)) ) {
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/* store sequence */
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size_t const rLength = ZSTD_count(ip0+4, ip0+4-rep_offset2, iend) + 4;
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{ U32 const tmpOff = rep_offset2; rep_offset2 = rep_offset1; rep_offset1 = tmpOff; } /* swap rep_offset2 <=> rep_offset1 */
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hashTable[ZSTD_hashPtr(ip0, hlog, mls)] = (U32)(ip0-base);
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ip0 += rLength;
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ZSTD_storeSeq(seqStore, 0 /*litLen*/, anchor, iend, 0 /*offCode*/, rLength-MINMATCH);
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anchor = ip0;
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continue; /* faster when present (confirmed on gcc-8) ... (?) */
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} } }
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goto _start;
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}
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size_t ZSTD_compressBlock_fast(
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ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
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void const* src, size_t srcSize)
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@ -193,13 +442,13 @@ size_t ZSTD_compressBlock_fast(
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{
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default: /* includes case 3 */
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case 4 :
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return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, 4);
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return ZSTD_compressBlock_fast_generic_pipelined(ms, seqStore, rep, src, srcSize, 4);
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case 5 :
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return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, 5);
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return ZSTD_compressBlock_fast_generic_pipelined(ms, seqStore, rep, src, srcSize, 5);
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case 6 :
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return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, 6);
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return ZSTD_compressBlock_fast_generic_pipelined(ms, seqStore, rep, src, srcSize, 6);
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case 7 :
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return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, 7);
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return ZSTD_compressBlock_fast_generic_pipelined(ms, seqStore, rep, src, srcSize, 7);
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}
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}
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@ -402,7 +651,7 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
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/* switch to "regular" variant if extDict is invalidated due to maxDistance */
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if (prefixStartIndex == dictStartIndex)
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return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, mls);
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return ZSTD_compressBlock_fast_generic_pipelined(ms, seqStore, rep, src, srcSize, mls);
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/* Search Loop */
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while (ip < ilimit) { /* < instead of <=, because (ip+1) */
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