FreeBSD/Linux Kernel Cross Reference
sys/contrib/zstd/lib/compress/zstd_ldm.c

     /*
      * Copyright (c) Yann Collet, Facebook, Inc.
      * All rights reserved.
      *
      * This source code is licensed under both the BSD-style license (found in the
      * LICENSE file in the root directory of this source tree) and the GPLv2 (found
      * in the COPYING file in the root directory of this source tree).
      * You may select, at your option, one of the above-listed licenses.
      */
    
    #include "zstd_ldm.h"
    
    #include "../common/debug.h"
    #include "../common/xxhash.h"
    #include "zstd_fast.h"          /* ZSTD_fillHashTable() */
    #include "zstd_double_fast.h"   /* ZSTD_fillDoubleHashTable() */
    #include "zstd_ldm_geartab.h"
    
    #define LDM_BUCKET_SIZE_LOG 3
    #define LDM_MIN_MATCH_LENGTH 64
    #define LDM_HASH_RLOG 7
    
    typedef struct {
        U64 rolling;
        U64 stopMask;
    } ldmRollingHashState_t;
    
    /** ZSTD_ldm_gear_init():
     *
     * Initializes the rolling hash state such that it will honor the
     * settings in params. */
    static void ZSTD_ldm_gear_init(ldmRollingHashState_t* state, ldmParams_t const* params)
    {
        unsigned maxBitsInMask = MIN(params->minMatchLength, 64);
        unsigned hashRateLog = params->hashRateLog;
    
        state->rolling = ~(U32)0;
    
        /* The choice of the splitting criterion is subject to two conditions:
         *   1. it has to trigger on average every 2^(hashRateLog) bytes;
         *   2. ideally, it has to depend on a window of minMatchLength bytes.
         *
         * In the gear hash algorithm, bit n depends on the last n bytes;
         * so in order to obtain a good quality splitting criterion it is
         * preferable to use bits with high weight.
         *
         * To match condition 1 we use a mask with hashRateLog bits set
         * and, because of the previous remark, we make sure these bits
         * have the highest possible weight while still respecting
         * condition 2.
         */
        if (hashRateLog > 0 && hashRateLog <= maxBitsInMask) {
            state->stopMask = (((U64)1 << hashRateLog) - 1) << (maxBitsInMask - hashRateLog);
        } else {
            /* In this degenerate case we simply honor the hash rate. */
            state->stopMask = ((U64)1 << hashRateLog) - 1;
        }
    }
    
    /** ZSTD_ldm_gear_reset()
     * Feeds [data, data + minMatchLength) into the hash without registering any
     * splits. This effectively resets the hash state. This is used when skipping
     * over data, either at the beginning of a block, or skipping sections.
     */
    static void ZSTD_ldm_gear_reset(ldmRollingHashState_t* state,
                                    BYTE const* data, size_t minMatchLength)
    {
        U64 hash = state->rolling;
        size_t n = 0;
    
    #define GEAR_ITER_ONCE() do {                                  \
            hash = (hash << 1) + ZSTD_ldm_gearTab[data[n] & 0xff]; \
            n += 1;                                                \
        } while (0)
        while (n + 3 < minMatchLength) {
            GEAR_ITER_ONCE();
            GEAR_ITER_ONCE();
            GEAR_ITER_ONCE();
            GEAR_ITER_ONCE();
        }
        while (n < minMatchLength) {
            GEAR_ITER_ONCE();
        }
    #undef GEAR_ITER_ONCE
    }
    
    /** ZSTD_ldm_gear_feed():
     *
     * Registers in the splits array all the split points found in the first
     * size bytes following the data pointer. This function terminates when
     * either all the data has been processed or LDM_BATCH_SIZE splits are
     * present in the splits array.
     *
     * Precondition: The splits array must not be full.
     * Returns: The number of bytes processed. */
    static size_t ZSTD_ldm_gear_feed(ldmRollingHashState_t* state,
                                     BYTE const* data, size_t size,
                                     size_t* splits, unsigned* numSplits)
    {
       size_t n;
       U64 hash, mask;
   
       hash = state->rolling;
       mask = state->stopMask;
       n = 0;
   
   #define GEAR_ITER_ONCE() do { \
           hash = (hash << 1) + ZSTD_ldm_gearTab[data[n] & 0xff]; \
           n += 1; \
           if (UNLIKELY((hash & mask) == 0)) { \
               splits[*numSplits] = n; \
               *numSplits += 1; \
               if (*numSplits == LDM_BATCH_SIZE) \
                   goto done; \
           } \
       } while (0)
   
       while (n + 3 < size) {
           GEAR_ITER_ONCE();
           GEAR_ITER_ONCE();
           GEAR_ITER_ONCE();
           GEAR_ITER_ONCE();
       }
       while (n < size) {
           GEAR_ITER_ONCE();
       }
   
   #undef GEAR_ITER_ONCE
   
   done:
       state->rolling = hash;
       return n;
   }
   
   void ZSTD_ldm_adjustParameters(ldmParams_t* params,
                                  ZSTD_compressionParameters const* cParams)
   {
       params->windowLog = cParams->windowLog;
       ZSTD_STATIC_ASSERT(LDM_BUCKET_SIZE_LOG <= ZSTD_LDM_BUCKETSIZELOG_MAX);
       DEBUGLOG(4, "ZSTD_ldm_adjustParameters");
       if (!params->bucketSizeLog) params->bucketSizeLog = LDM_BUCKET_SIZE_LOG;
       if (!params->minMatchLength) params->minMatchLength = LDM_MIN_MATCH_LENGTH;
       if (params->hashLog == 0) {
           params->hashLog = MAX(ZSTD_HASHLOG_MIN, params->windowLog - LDM_HASH_RLOG);
           assert(params->hashLog <= ZSTD_HASHLOG_MAX);
       }
       if (params->hashRateLog == 0) {
           params->hashRateLog = params->windowLog < params->hashLog
                                      ? 0
                                      : params->windowLog - params->hashLog;
       }
       params->bucketSizeLog = MIN(params->bucketSizeLog, params->hashLog);
   }
   
   size_t ZSTD_ldm_getTableSize(ldmParams_t params)
   {
       size_t const ldmHSize = ((size_t)1) << params.hashLog;
       size_t const ldmBucketSizeLog = MIN(params.bucketSizeLog, params.hashLog);
       size_t const ldmBucketSize = ((size_t)1) << (params.hashLog - ldmBucketSizeLog);
       size_t const totalSize = ZSTD_cwksp_alloc_size(ldmBucketSize)
                              + ZSTD_cwksp_alloc_size(ldmHSize * sizeof(ldmEntry_t));
       return params.enableLdm == ZSTD_ps_enable ? totalSize : 0;
   }
   
   size_t ZSTD_ldm_getMaxNbSeq(ldmParams_t params, size_t maxChunkSize)
   {
       return params.enableLdm == ZSTD_ps_enable ? (maxChunkSize / params.minMatchLength) : 0;
   }
   
   /** ZSTD_ldm_getBucket() :
    *  Returns a pointer to the start of the bucket associated with hash. */
   static ldmEntry_t* ZSTD_ldm_getBucket(
           ldmState_t* ldmState, size_t hash, ldmParams_t const ldmParams)
   {
       return ldmState->hashTable + (hash << ldmParams.bucketSizeLog);
   }
   
   /** ZSTD_ldm_insertEntry() :
    *  Insert the entry with corresponding hash into the hash table */
   static void ZSTD_ldm_insertEntry(ldmState_t* ldmState,
                                    size_t const hash, const ldmEntry_t entry,
                                    ldmParams_t const ldmParams)
   {
       BYTE* const pOffset = ldmState->bucketOffsets + hash;
       unsigned const offset = *pOffset;
   
       *(ZSTD_ldm_getBucket(ldmState, hash, ldmParams) + offset) = entry;
       *pOffset = (BYTE)((offset + 1) & ((1u << ldmParams.bucketSizeLog) - 1));
   
   }
   
   /** ZSTD_ldm_countBackwardsMatch() :
    *  Returns the number of bytes that match backwards before pIn and pMatch.
    *
    *  We count only bytes where pMatch >= pBase and pIn >= pAnchor. */
   static size_t ZSTD_ldm_countBackwardsMatch(
               const BYTE* pIn, const BYTE* pAnchor,
               const BYTE* pMatch, const BYTE* pMatchBase)
   {
       size_t matchLength = 0;
       while (pIn > pAnchor && pMatch > pMatchBase && pIn[-1] == pMatch[-1]) {
           pIn--;
           pMatch--;
           matchLength++;
       }
       return matchLength;
   }
   
   /** ZSTD_ldm_countBackwardsMatch_2segments() :
    *  Returns the number of bytes that match backwards from pMatch,
    *  even with the backwards match spanning 2 different segments.
    *
    *  On reaching `pMatchBase`, start counting from mEnd */
   static size_t ZSTD_ldm_countBackwardsMatch_2segments(
                       const BYTE* pIn, const BYTE* pAnchor,
                       const BYTE* pMatch, const BYTE* pMatchBase,
                       const BYTE* pExtDictStart, const BYTE* pExtDictEnd)
   {
       size_t matchLength = ZSTD_ldm_countBackwardsMatch(pIn, pAnchor, pMatch, pMatchBase);
       if (pMatch - matchLength != pMatchBase || pMatchBase == pExtDictStart) {
           /* If backwards match is entirely in the extDict or prefix, immediately return */
           return matchLength;
       }
       DEBUGLOG(7, "ZSTD_ldm_countBackwardsMatch_2segments: found 2-parts backwards match (length in prefix==%zu)", matchLength);
       matchLength += ZSTD_ldm_countBackwardsMatch(pIn - matchLength, pAnchor, pExtDictEnd, pExtDictStart);
       DEBUGLOG(7, "final backwards match length = %zu", matchLength);
       return matchLength;
   }
   
   /** ZSTD_ldm_fillFastTables() :
    *
    *  Fills the relevant tables for the ZSTD_fast and ZSTD_dfast strategies.
    *  This is similar to ZSTD_loadDictionaryContent.
    *
    *  The tables for the other strategies are filled within their
    *  block compressors. */
   static size_t ZSTD_ldm_fillFastTables(ZSTD_matchState_t* ms,
                                         void const* end)
   {
       const BYTE* const iend = (const BYTE*)end;
   
       switch(ms->cParams.strategy)
       {
       case ZSTD_fast:
           ZSTD_fillHashTable(ms, iend, ZSTD_dtlm_fast);
           break;
   
       case ZSTD_dfast:
           ZSTD_fillDoubleHashTable(ms, iend, ZSTD_dtlm_fast);
           break;
   
       case ZSTD_greedy:
       case ZSTD_lazy:
       case ZSTD_lazy2:
       case ZSTD_btlazy2:
       case ZSTD_btopt:
       case ZSTD_btultra:
       case ZSTD_btultra2:
           break;
       default:
           assert(0);  /* not possible : not a valid strategy id */
       }
   
       return 0;
   }
   
   void ZSTD_ldm_fillHashTable(
               ldmState_t* ldmState, const BYTE* ip,
               const BYTE* iend, ldmParams_t const* params)
   {
       U32 const minMatchLength = params->minMatchLength;
       U32 const hBits = params->hashLog - params->bucketSizeLog;
       BYTE const* const base = ldmState->window.base;
       BYTE const* const istart = ip;
       ldmRollingHashState_t hashState;
       size_t* const splits = ldmState->splitIndices;
       unsigned numSplits;
   
       DEBUGLOG(5, "ZSTD_ldm_fillHashTable");
   
       ZSTD_ldm_gear_init(&hashState, params);
       while (ip < iend) {
           size_t hashed;
           unsigned n;
   
           numSplits = 0;
           hashed = ZSTD_ldm_gear_feed(&hashState, ip, iend - ip, splits, &numSplits);
   
           for (n = 0; n < numSplits; n++) {
               if (ip + splits[n] >= istart + minMatchLength) {
                   BYTE const* const split = ip + splits[n] - minMatchLength;
                   U64 const xxhash = XXH64(split, minMatchLength, 0);
                   U32 const hash = (U32)(xxhash & (((U32)1 << hBits) - 1));
                   ldmEntry_t entry;
   
                   entry.offset = (U32)(split - base);
                   entry.checksum = (U32)(xxhash >> 32);
                   ZSTD_ldm_insertEntry(ldmState, hash, entry, *params);
               }
           }
   
           ip += hashed;
       }
   }
   
   
   /** ZSTD_ldm_limitTableUpdate() :
    *
    *  Sets cctx->nextToUpdate to a position corresponding closer to anchor
    *  if it is far way
    *  (after a long match, only update tables a limited amount). */
   static void ZSTD_ldm_limitTableUpdate(ZSTD_matchState_t* ms, const BYTE* anchor)
   {
       U32 const curr = (U32)(anchor - ms->window.base);
       if (curr > ms->nextToUpdate + 1024) {
           ms->nextToUpdate =
               curr - MIN(512, curr - ms->nextToUpdate - 1024);
       }
   }
   
   static size_t ZSTD_ldm_generateSequences_internal(
           ldmState_t* ldmState, rawSeqStore_t* rawSeqStore,
           ldmParams_t const* params, void const* src, size_t srcSize)
   {
       /* LDM parameters */
       int const extDict = ZSTD_window_hasExtDict(ldmState->window);
       U32 const minMatchLength = params->minMatchLength;
       U32 const entsPerBucket = 1U << params->bucketSizeLog;
       U32 const hBits = params->hashLog - params->bucketSizeLog;
       /* Prefix and extDict parameters */
       U32 const dictLimit = ldmState->window.dictLimit;
       U32 const lowestIndex = extDict ? ldmState->window.lowLimit : dictLimit;
       BYTE const* const base = ldmState->window.base;
       BYTE const* const dictBase = extDict ? ldmState->window.dictBase : NULL;
       BYTE const* const dictStart = extDict ? dictBase + lowestIndex : NULL;
       BYTE const* const dictEnd = extDict ? dictBase + dictLimit : NULL;
       BYTE const* const lowPrefixPtr = base + dictLimit;
       /* Input bounds */
       BYTE const* const istart = (BYTE const*)src;
       BYTE const* const iend = istart + srcSize;
       BYTE const* const ilimit = iend - HASH_READ_SIZE;
       /* Input positions */
       BYTE const* anchor = istart;
       BYTE const* ip = istart;
       /* Rolling hash state */
       ldmRollingHashState_t hashState;
       /* Arrays for staged-processing */
       size_t* const splits = ldmState->splitIndices;
       ldmMatchCandidate_t* const candidates = ldmState->matchCandidates;
       unsigned numSplits;
   
       if (srcSize < minMatchLength)
           return iend - anchor;
   
       /* Initialize the rolling hash state with the first minMatchLength bytes */
       ZSTD_ldm_gear_init(&hashState, params);
       ZSTD_ldm_gear_reset(&hashState, ip, minMatchLength);
       ip += minMatchLength;
   
       while (ip < ilimit) {
           size_t hashed;
           unsigned n;
   
           numSplits = 0;
           hashed = ZSTD_ldm_gear_feed(&hashState, ip, ilimit - ip,
                                       splits, &numSplits);
   
           for (n = 0; n < numSplits; n++) {
               BYTE const* const split = ip + splits[n] - minMatchLength;
               U64 const xxhash = XXH64(split, minMatchLength, 0);
               U32 const hash = (U32)(xxhash & (((U32)1 << hBits) - 1));
   
               candidates[n].split = split;
               candidates[n].hash = hash;
               candidates[n].checksum = (U32)(xxhash >> 32);
               candidates[n].bucket = ZSTD_ldm_getBucket(ldmState, hash, *params);
               PREFETCH_L1(candidates[n].bucket);
           }
   
           for (n = 0; n < numSplits; n++) {
               size_t forwardMatchLength = 0, backwardMatchLength = 0,
                      bestMatchLength = 0, mLength;
               U32 offset;
               BYTE const* const split = candidates[n].split;
               U32 const checksum = candidates[n].checksum;
               U32 const hash = candidates[n].hash;
               ldmEntry_t* const bucket = candidates[n].bucket;
               ldmEntry_t const* cur;
               ldmEntry_t const* bestEntry = NULL;
               ldmEntry_t newEntry;
   
               newEntry.offset = (U32)(split - base);
               newEntry.checksum = checksum;
   
               /* If a split point would generate a sequence overlapping with
                * the previous one, we merely register it in the hash table and
                * move on */
               if (split < anchor) {
                   ZSTD_ldm_insertEntry(ldmState, hash, newEntry, *params);
                   continue;
               }
   
               for (cur = bucket; cur < bucket + entsPerBucket; cur++) {
                   size_t curForwardMatchLength, curBackwardMatchLength,
                          curTotalMatchLength;
                   if (cur->checksum != checksum || cur->offset <= lowestIndex) {
                       continue;
                   }
                   if (extDict) {
                       BYTE const* const curMatchBase =
                           cur->offset < dictLimit ? dictBase : base;
                       BYTE const* const pMatch = curMatchBase + cur->offset;
                       BYTE const* const matchEnd =
                           cur->offset < dictLimit ? dictEnd : iend;
                       BYTE const* const lowMatchPtr =
                           cur->offset < dictLimit ? dictStart : lowPrefixPtr;
                       curForwardMatchLength =
                           ZSTD_count_2segments(split, pMatch, iend, matchEnd, lowPrefixPtr);
                       if (curForwardMatchLength < minMatchLength) {
                           continue;
                       }
                       curBackwardMatchLength = ZSTD_ldm_countBackwardsMatch_2segments(
                               split, anchor, pMatch, lowMatchPtr, dictStart, dictEnd);
                   } else { /* !extDict */
                       BYTE const* const pMatch = base + cur->offset;
                       curForwardMatchLength = ZSTD_count(split, pMatch, iend);
                       if (curForwardMatchLength < minMatchLength) {
                           continue;
                       }
                       curBackwardMatchLength =
                           ZSTD_ldm_countBackwardsMatch(split, anchor, pMatch, lowPrefixPtr);
                   }
                   curTotalMatchLength = curForwardMatchLength + curBackwardMatchLength;
   
                   if (curTotalMatchLength > bestMatchLength) {
                       bestMatchLength = curTotalMatchLength;
                       forwardMatchLength = curForwardMatchLength;
                       backwardMatchLength = curBackwardMatchLength;
                       bestEntry = cur;
                   }
               }
   
               /* No match found -- insert an entry into the hash table
                * and process the next candidate match */
               if (bestEntry == NULL) {
                   ZSTD_ldm_insertEntry(ldmState, hash, newEntry, *params);
                   continue;
               }
   
               /* Match found */
               offset = (U32)(split - base) - bestEntry->offset;
               mLength = forwardMatchLength + backwardMatchLength;
               {
                   rawSeq* const seq = rawSeqStore->seq + rawSeqStore->size;
   
                   /* Out of sequence storage */
                   if (rawSeqStore->size == rawSeqStore->capacity)
                       return ERROR(dstSize_tooSmall);
                   seq->litLength = (U32)(split - backwardMatchLength - anchor);
                   seq->matchLength = (U32)mLength;
                   seq->offset = offset;
                   rawSeqStore->size++;
               }
   
               /* Insert the current entry into the hash table --- it must be
                * done after the previous block to avoid clobbering bestEntry */
               ZSTD_ldm_insertEntry(ldmState, hash, newEntry, *params);
   
               anchor = split + forwardMatchLength;
   
               /* If we find a match that ends after the data that we've hashed
                * then we have a repeating, overlapping, pattern. E.g. all zeros.
                * If one repetition of the pattern matches our `stopMask` then all
                * repetitions will. We don't need to insert them all into out table,
                * only the first one. So skip over overlapping matches.
                * This is a major speed boost (20x) for compressing a single byte
                * repeated, when that byte ends up in the table.
                */
               if (anchor > ip + hashed) {
                   ZSTD_ldm_gear_reset(&hashState, anchor - minMatchLength, minMatchLength);
                   /* Continue the outer loop at anchor (ip + hashed == anchor). */
                   ip = anchor - hashed;
                   break;
               }
           }
   
           ip += hashed;
       }
   
       return iend - anchor;
   }
   
   /*! ZSTD_ldm_reduceTable() :
    *  reduce table indexes by `reducerValue` */
   static void ZSTD_ldm_reduceTable(ldmEntry_t* const table, U32 const size,
                                    U32 const reducerValue)
   {
       U32 u;
       for (u = 0; u < size; u++) {
           if (table[u].offset < reducerValue) table[u].offset = 0;
           else table[u].offset -= reducerValue;
       }
   }
   
   size_t ZSTD_ldm_generateSequences(
           ldmState_t* ldmState, rawSeqStore_t* sequences,
           ldmParams_t const* params, void const* src, size_t srcSize)
   {
       U32 const maxDist = 1U << params->windowLog;
       BYTE const* const istart = (BYTE const*)src;
       BYTE const* const iend = istart + srcSize;
       size_t const kMaxChunkSize = 1 << 20;
       size_t const nbChunks = (srcSize / kMaxChunkSize) + ((srcSize % kMaxChunkSize) != 0);
       size_t chunk;
       size_t leftoverSize = 0;
   
       assert(ZSTD_CHUNKSIZE_MAX >= kMaxChunkSize);
       /* Check that ZSTD_window_update() has been called for this chunk prior
        * to passing it to this function.
        */
       assert(ldmState->window.nextSrc >= (BYTE const*)src + srcSize);
       /* The input could be very large (in zstdmt), so it must be broken up into
        * chunks to enforce the maximum distance and handle overflow correction.
        */
       assert(sequences->pos <= sequences->size);
       assert(sequences->size <= sequences->capacity);
       for (chunk = 0; chunk < nbChunks && sequences->size < sequences->capacity; ++chunk) {
           BYTE const* const chunkStart = istart + chunk * kMaxChunkSize;
           size_t const remaining = (size_t)(iend - chunkStart);
           BYTE const *const chunkEnd =
               (remaining < kMaxChunkSize) ? iend : chunkStart + kMaxChunkSize;
           size_t const chunkSize = chunkEnd - chunkStart;
           size_t newLeftoverSize;
           size_t const prevSize = sequences->size;
   
           assert(chunkStart < iend);
           /* 1. Perform overflow correction if necessary. */
           if (ZSTD_window_needOverflowCorrection(ldmState->window, 0, maxDist, ldmState->loadedDictEnd, chunkStart, chunkEnd)) {
               U32 const ldmHSize = 1U << params->hashLog;
               U32 const correction = ZSTD_window_correctOverflow(
                   &ldmState->window, /* cycleLog */ 0, maxDist, chunkStart);
               ZSTD_ldm_reduceTable(ldmState->hashTable, ldmHSize, correction);
               /* invalidate dictionaries on overflow correction */
               ldmState->loadedDictEnd = 0;
           }
           /* 2. We enforce the maximum offset allowed.
            *
            * kMaxChunkSize should be small enough that we don't lose too much of
            * the window through early invalidation.
            * TODO: * Test the chunk size.
            *       * Try invalidation after the sequence generation and test the
            *         the offset against maxDist directly.
            *
            * NOTE: Because of dictionaries + sequence splitting we MUST make sure
            * that any offset used is valid at the END of the sequence, since it may
            * be split into two sequences. This condition holds when using
            * ZSTD_window_enforceMaxDist(), but if we move to checking offsets
            * against maxDist directly, we'll have to carefully handle that case.
            */
           ZSTD_window_enforceMaxDist(&ldmState->window, chunkEnd, maxDist, &ldmState->loadedDictEnd, NULL);
           /* 3. Generate the sequences for the chunk, and get newLeftoverSize. */
           newLeftoverSize = ZSTD_ldm_generateSequences_internal(
               ldmState, sequences, params, chunkStart, chunkSize);
           if (ZSTD_isError(newLeftoverSize))
               return newLeftoverSize;
           /* 4. We add the leftover literals from previous iterations to the first
            *    newly generated sequence, or add the `newLeftoverSize` if none are
            *    generated.
            */
           /* Prepend the leftover literals from the last call */
           if (prevSize < sequences->size) {
               sequences->seq[prevSize].litLength += (U32)leftoverSize;
               leftoverSize = newLeftoverSize;
           } else {
               assert(newLeftoverSize == chunkSize);
               leftoverSize += chunkSize;
           }
       }
       return 0;
   }
   
   void
   ZSTD_ldm_skipSequences(rawSeqStore_t* rawSeqStore, size_t srcSize, U32 const minMatch)
   {
       while (srcSize > 0 && rawSeqStore->pos < rawSeqStore->size) {
           rawSeq* seq = rawSeqStore->seq + rawSeqStore->pos;
           if (srcSize <= seq->litLength) {
               /* Skip past srcSize literals */
               seq->litLength -= (U32)srcSize;
               return;
           }
           srcSize -= seq->litLength;
           seq->litLength = 0;
           if (srcSize < seq->matchLength) {
               /* Skip past the first srcSize of the match */
               seq->matchLength -= (U32)srcSize;
               if (seq->matchLength < minMatch) {
                   /* The match is too short, omit it */
                   if (rawSeqStore->pos + 1 < rawSeqStore->size) {
                       seq[1].litLength += seq[0].matchLength;
                   }
                   rawSeqStore->pos++;
               }
               return;
           }
           srcSize -= seq->matchLength;
           seq->matchLength = 0;
           rawSeqStore->pos++;
       }
   }
   
   /**
    * If the sequence length is longer than remaining then the sequence is split
    * between this block and the next.
    *
    * Returns the current sequence to handle, or if the rest of the block should
    * be literals, it returns a sequence with offset == 0.
    */
   static rawSeq maybeSplitSequence(rawSeqStore_t* rawSeqStore,
                                    U32 const remaining, U32 const minMatch)
   {
       rawSeq sequence = rawSeqStore->seq[rawSeqStore->pos];
       assert(sequence.offset > 0);
       /* Likely: No partial sequence */
       if (remaining >= sequence.litLength + sequence.matchLength) {
           rawSeqStore->pos++;
           return sequence;
       }
       /* Cut the sequence short (offset == 0 ==> rest is literals). */
       if (remaining <= sequence.litLength) {
           sequence.offset = 0;
       } else if (remaining < sequence.litLength + sequence.matchLength) {
           sequence.matchLength = remaining - sequence.litLength;
           if (sequence.matchLength < minMatch) {
               sequence.offset = 0;
           }
       }
       /* Skip past `remaining` bytes for the future sequences. */
       ZSTD_ldm_skipSequences(rawSeqStore, remaining, minMatch);
       return sequence;
   }
   
   void ZSTD_ldm_skipRawSeqStoreBytes(rawSeqStore_t* rawSeqStore, size_t nbBytes) {
       U32 currPos = (U32)(rawSeqStore->posInSequence + nbBytes);
       while (currPos && rawSeqStore->pos < rawSeqStore->size) {
           rawSeq currSeq = rawSeqStore->seq[rawSeqStore->pos];
           if (currPos >= currSeq.litLength + currSeq.matchLength) {
               currPos -= currSeq.litLength + currSeq.matchLength;
               rawSeqStore->pos++;
           } else {
               rawSeqStore->posInSequence = currPos;
               break;
           }
       }
       if (currPos == 0 || rawSeqStore->pos == rawSeqStore->size) {
           rawSeqStore->posInSequence = 0;
       }
   }
   
   size_t ZSTD_ldm_blockCompress(rawSeqStore_t* rawSeqStore,
       ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
       ZSTD_paramSwitch_e useRowMatchFinder,
       void const* src, size_t srcSize)
   {
       const ZSTD_compressionParameters* const cParams = &ms->cParams;
       unsigned const minMatch = cParams->minMatch;
       ZSTD_blockCompressor const blockCompressor =
           ZSTD_selectBlockCompressor(cParams->strategy, useRowMatchFinder, ZSTD_matchState_dictMode(ms));
       /* Input bounds */
       BYTE const* const istart = (BYTE const*)src;
       BYTE const* const iend = istart + srcSize;
       /* Input positions */
       BYTE const* ip = istart;
   
       DEBUGLOG(5, "ZSTD_ldm_blockCompress: srcSize=%zu", srcSize);
       /* If using opt parser, use LDMs only as candidates rather than always accepting them */
       if (cParams->strategy >= ZSTD_btopt) {
           size_t lastLLSize;
           ms->ldmSeqStore = rawSeqStore;
           lastLLSize = blockCompressor(ms, seqStore, rep, src, srcSize);
           ZSTD_ldm_skipRawSeqStoreBytes(rawSeqStore, srcSize);
           return lastLLSize;
       }
   
       assert(rawSeqStore->pos <= rawSeqStore->size);
       assert(rawSeqStore->size <= rawSeqStore->capacity);
       /* Loop through each sequence and apply the block compressor to the literals */
       while (rawSeqStore->pos < rawSeqStore->size && ip < iend) {
           /* maybeSplitSequence updates rawSeqStore->pos */
           rawSeq const sequence = maybeSplitSequence(rawSeqStore,
                                                      (U32)(iend - ip), minMatch);
           int i;
           /* End signal */
           if (sequence.offset == 0)
               break;
   
           assert(ip + sequence.litLength + sequence.matchLength <= iend);
   
           /* Fill tables for block compressor */
           ZSTD_ldm_limitTableUpdate(ms, ip);
           ZSTD_ldm_fillFastTables(ms, ip);
           /* Run the block compressor */
           DEBUGLOG(5, "pos %u : calling block compressor on segment of size %u", (unsigned)(ip-istart), sequence.litLength);
           {
               size_t const newLitLength =
                   blockCompressor(ms, seqStore, rep, ip, sequence.litLength);
               ip += sequence.litLength;
               /* Update the repcodes */
               for (i = ZSTD_REP_NUM - 1; i > 0; i--)
                   rep[i] = rep[i-1];
               rep[0] = sequence.offset;
               /* Store the sequence */
               ZSTD_storeSeq(seqStore, newLitLength, ip - newLitLength, iend,
                             STORE_OFFSET(sequence.offset),
                             sequence.matchLength);
               ip += sequence.matchLength;
           }
       }
       /* Fill the tables for the block compressor */
       ZSTD_ldm_limitTableUpdate(ms, ip);
       ZSTD_ldm_fillFastTables(ms, ip);
       /* Compress the last literals */
       return blockCompressor(ms, seqStore, rep, ip, iend - ip);
   }

Cache object: fdd710b9e332df224be1e794ede95b6d