view contrib/python-zstandard/zstd/compress/zstd_double_fast.c @ 40121:73fef626dae3

zstandard: vendor python-zstandard 0.10.1

This was just released.

The upstream source distribution from PyPI was extracted. Unwanted
files were removed.

The clang-format ignore list was updated to reflect the new source
of files.

setup.py was updated to pass a new argument to python-zstandard's
function for returning an Extension instance. Upstream had to change
to use relative paths because Python 3.7's packaging doesn't
seem to like absolute paths when defining sources, includes, etc.
The default relative path calculation is relative to setup_zstd.py
which is different from the directory of Mercurial's setup.py.

The project contains a vendored copy of zstandard 1.3.6. The old
version was 1.3.4.

The API should be backwards compatible and nothing in core should
need adjusted. However, there is a new "chunker" API that we
may find useful in places where we want to emit compressed chunks
of a fixed size.

There are a pair of bug fixes in 0.10.0 with regards to
compressobj() and decompressobj() when block flushing is used. I
actually found these bugs when introducing these APIs in Mercurial!
But existing Mercurial code is not affected because we don't
perform block flushing.

# no-check-commit because 3rd party code has different style guidelines

Differential Revision: https://phab.mercurial-scm.org/D4911

/*
 * Copyright (c) 2016-present, 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_compress_internal.h"
#include "zstd_double_fast.h"


void ZSTD_fillDoubleHashTable(ZSTD_matchState_t* ms,
                              void const* end, ZSTD_dictTableLoadMethod_e dtlm)
{
    const ZSTD_compressionParameters* const cParams = &ms->cParams;
    U32* const hashLarge = ms->hashTable;
    U32  const hBitsL = cParams->hashLog;
    U32  const mls = cParams->searchLength;
    U32* const hashSmall = ms->chainTable;
    U32  const hBitsS = cParams->chainLog;
    const BYTE* const base = ms->window.base;
    const BYTE* ip = base + ms->nextToUpdate;
    const BYTE* const iend = ((const BYTE*)end) - HASH_READ_SIZE;
    const U32 fastHashFillStep = 3;

    /* Always insert every fastHashFillStep position into the hash tables.
     * Insert the other positions into the large hash table if their entry
     * is empty.
     */
    for (; ip + fastHashFillStep - 1 <= iend; ip += fastHashFillStep) {
        U32 const current = (U32)(ip - base);
        U32 i;
        for (i = 0; i < fastHashFillStep; ++i) {
            size_t const smHash = ZSTD_hashPtr(ip + i, hBitsS, mls);
            size_t const lgHash = ZSTD_hashPtr(ip + i, hBitsL, 8);
            if (i == 0)
                hashSmall[smHash] = current + i;
            if (i == 0 || hashLarge[lgHash] == 0)
                hashLarge[lgHash] = current + i;
            /* Only load extra positions for ZSTD_dtlm_full */
            if (dtlm == ZSTD_dtlm_fast)
                break;
        }
    }
}


FORCE_INLINE_TEMPLATE
size_t ZSTD_compressBlock_doubleFast_generic(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize,
        U32 const mls /* template */, ZSTD_dictMode_e const dictMode)
{
    ZSTD_compressionParameters const* cParams = &ms->cParams;
    U32* const hashLong = ms->hashTable;
    const U32 hBitsL = cParams->hashLog;
    U32* const hashSmall = ms->chainTable;
    const U32 hBitsS = cParams->chainLog;
    const BYTE* const base = ms->window.base;
    const BYTE* const istart = (const BYTE*)src;
    const BYTE* ip = istart;
    const BYTE* anchor = istart;
    const U32 prefixLowestIndex = ms->window.dictLimit;
    const BYTE* const prefixLowest = base + prefixLowestIndex;
    const BYTE* const iend = istart + srcSize;
    const BYTE* const ilimit = iend - HASH_READ_SIZE;
    U32 offset_1=rep[0], offset_2=rep[1];
    U32 offsetSaved = 0;

    const ZSTD_matchState_t* const dms = ms->dictMatchState;
    const ZSTD_compressionParameters* const dictCParams =
                                     dictMode == ZSTD_dictMatchState ?
                                     &dms->cParams : NULL;
    const U32* const dictHashLong  = dictMode == ZSTD_dictMatchState ?
                                     dms->hashTable : NULL;
    const U32* const dictHashSmall = dictMode == ZSTD_dictMatchState ?
                                     dms->chainTable : NULL;
    const U32 dictStartIndex       = dictMode == ZSTD_dictMatchState ?
                                     dms->window.dictLimit : 0;
    const BYTE* const dictBase     = dictMode == ZSTD_dictMatchState ?
                                     dms->window.base : NULL;
    const BYTE* const dictStart    = dictMode == ZSTD_dictMatchState ?
                                     dictBase + dictStartIndex : NULL;
    const BYTE* const dictEnd      = dictMode == ZSTD_dictMatchState ?
                                     dms->window.nextSrc : NULL;
    const U32 dictIndexDelta       = dictMode == ZSTD_dictMatchState ?
                                     prefixLowestIndex - (U32)(dictEnd - dictBase) :
                                     0;
    const U32 dictHBitsL           = dictMode == ZSTD_dictMatchState ?
                                     dictCParams->hashLog : hBitsL;
    const U32 dictHBitsS           = dictMode == ZSTD_dictMatchState ?
                                     dictCParams->chainLog : hBitsS;
    const U32 dictAndPrefixLength  = (U32)(ip - prefixLowest + dictEnd - dictStart);

    assert(dictMode == ZSTD_noDict || dictMode == ZSTD_dictMatchState);

    /* init */
    ip += (dictAndPrefixLength == 0);
    if (dictMode == ZSTD_noDict) {
        U32 const maxRep = (U32)(ip - prefixLowest);
        if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0;
        if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0;
    }
    if (dictMode == ZSTD_dictMatchState) {
        /* dictMatchState repCode checks don't currently handle repCode == 0
         * disabling. */
        assert(offset_1 <= dictAndPrefixLength);
        assert(offset_2 <= dictAndPrefixLength);
    }

    /* Main Search Loop */
    while (ip < ilimit) {   /* < instead of <=, because repcode check at (ip+1) */
        size_t mLength;
        U32 offset;
        size_t const h2 = ZSTD_hashPtr(ip, hBitsL, 8);
        size_t const h = ZSTD_hashPtr(ip, hBitsS, mls);
        size_t const dictHL = ZSTD_hashPtr(ip, dictHBitsL, 8);
        size_t const dictHS = ZSTD_hashPtr(ip, dictHBitsS, mls);
        U32 const current = (U32)(ip-base);
        U32 const matchIndexL = hashLong[h2];
        U32 matchIndexS = hashSmall[h];
        const BYTE* matchLong = base + matchIndexL;
        const BYTE* match = base + matchIndexS;
        const U32 repIndex = current + 1 - offset_1;
        const BYTE* repMatch = (dictMode == ZSTD_dictMatchState
                            && repIndex < prefixLowestIndex) ?
                               dictBase + (repIndex - dictIndexDelta) :
                               base + repIndex;
        hashLong[h2] = hashSmall[h] = current;   /* update hash tables */

        /* check dictMatchState repcode */
        if (dictMode == ZSTD_dictMatchState
            && ((U32)((prefixLowestIndex-1) - repIndex) >= 3 /* intentional underflow */)
            && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
            const BYTE* repMatchEnd = repIndex < prefixLowestIndex ? dictEnd : iend;
            mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixLowest) + 4;
            ip++;
            ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
            goto _match_stored;
        }

        /* check noDict repcode */
        if ( dictMode == ZSTD_noDict
          && ((offset_1 > 0) & (MEM_read32(ip+1-offset_1) == MEM_read32(ip+1)))) {
            mLength = ZSTD_count(ip+1+4, ip+1+4-offset_1, iend) + 4;
            ip++;
            ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
            goto _match_stored;
        }

        if (matchIndexL > prefixLowestIndex) {
            /* check prefix long match */
            if (MEM_read64(matchLong) == MEM_read64(ip)) {
                mLength = ZSTD_count(ip+8, matchLong+8, iend) + 8;
                offset = (U32)(ip-matchLong);
                while (((ip>anchor) & (matchLong>prefixLowest)) && (ip[-1] == matchLong[-1])) { ip--; matchLong--; mLength++; } /* catch up */
                goto _match_found;
            }
        } else if (dictMode == ZSTD_dictMatchState) {
            /* check dictMatchState long match */
            U32 const dictMatchIndexL = dictHashLong[dictHL];
            const BYTE* dictMatchL = dictBase + dictMatchIndexL;
            assert(dictMatchL < dictEnd);

            if (dictMatchL > dictStart && MEM_read64(dictMatchL) == MEM_read64(ip)) {
                mLength = ZSTD_count_2segments(ip+8, dictMatchL+8, iend, dictEnd, prefixLowest) + 8;
                offset = (U32)(current - dictMatchIndexL - dictIndexDelta);
                while (((ip>anchor) & (dictMatchL>dictStart)) && (ip[-1] == dictMatchL[-1])) { ip--; dictMatchL--; mLength++; } /* catch up */
                goto _match_found;
            }
        }

        if (matchIndexS > prefixLowestIndex) {
            /* check prefix short match */
            if (MEM_read32(match) == MEM_read32(ip)) {
                goto _search_next_long;
            }
        } else if (dictMode == ZSTD_dictMatchState) {
            /* check dictMatchState short match */
            U32 const dictMatchIndexS = dictHashSmall[dictHS];
            match = dictBase + dictMatchIndexS;
            matchIndexS = dictMatchIndexS + dictIndexDelta;

            if (match > dictStart && MEM_read32(match) == MEM_read32(ip)) {
                goto _search_next_long;
            }
        }

        ip += ((ip-anchor) >> kSearchStrength) + 1;
        continue;

_search_next_long:

        {
            size_t const hl3 = ZSTD_hashPtr(ip+1, hBitsL, 8);
            size_t const dictHLNext = ZSTD_hashPtr(ip+1, dictHBitsL, 8);
            U32 const matchIndexL3 = hashLong[hl3];
            const BYTE* matchL3 = base + matchIndexL3;
            hashLong[hl3] = current + 1;

            /* check prefix long +1 match */
            if (matchIndexL3 > prefixLowestIndex) {
                if (MEM_read64(matchL3) == MEM_read64(ip+1)) {
                    mLength = ZSTD_count(ip+9, matchL3+8, iend) + 8;
                    ip++;
                    offset = (U32)(ip-matchL3);
                    while (((ip>anchor) & (matchL3>prefixLowest)) && (ip[-1] == matchL3[-1])) { ip--; matchL3--; mLength++; } /* catch up */
                    goto _match_found;
                }
            } else if (dictMode == ZSTD_dictMatchState) {
                /* check dict long +1 match */
                U32 const dictMatchIndexL3 = dictHashLong[dictHLNext];
                const BYTE* dictMatchL3 = dictBase + dictMatchIndexL3;
                assert(dictMatchL3 < dictEnd);
                if (dictMatchL3 > dictStart && MEM_read64(dictMatchL3) == MEM_read64(ip+1)) {
                    mLength = ZSTD_count_2segments(ip+1+8, dictMatchL3+8, iend, dictEnd, prefixLowest) + 8;
                    ip++;
                    offset = (U32)(current + 1 - dictMatchIndexL3 - dictIndexDelta);
                    while (((ip>anchor) & (dictMatchL3>dictStart)) && (ip[-1] == dictMatchL3[-1])) { ip--; dictMatchL3--; mLength++; } /* catch up */
                    goto _match_found;
                }
            }
        }

        /* if no long +1 match, explore the short match we found */
        if (dictMode == ZSTD_dictMatchState && matchIndexS < prefixLowestIndex) {
            mLength = ZSTD_count_2segments(ip+4, match+4, iend, dictEnd, prefixLowest) + 4;
            offset = (U32)(current - matchIndexS);
            while (((ip>anchor) & (match>dictStart)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
        } else {
            mLength = ZSTD_count(ip+4, match+4, iend) + 4;
            offset = (U32)(ip - match);
            while (((ip>anchor) & (match>prefixLowest)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
        }

        /* fall-through */

_match_found:
        offset_2 = offset_1;
        offset_1 = offset;

        ZSTD_storeSeq(seqStore, ip-anchor, anchor, offset + ZSTD_REP_MOVE, mLength-MINMATCH);

_match_stored:
        /* match found */
        ip += mLength;
        anchor = ip;

        if (ip <= ilimit) {
            /* Fill Table */
            hashLong[ZSTD_hashPtr(base+current+2, hBitsL, 8)] =
                hashSmall[ZSTD_hashPtr(base+current+2, hBitsS, mls)] = current+2;  /* here because current+2 could be > iend-8 */
            hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] =
                hashSmall[ZSTD_hashPtr(ip-2, hBitsS, mls)] = (U32)(ip-2-base);

            /* check immediate repcode */
            if (dictMode == ZSTD_dictMatchState) {
                while (ip <= ilimit) {
                    U32 const current2 = (U32)(ip-base);
                    U32 const repIndex2 = current2 - offset_2;
                    const BYTE* repMatch2 = dictMode == ZSTD_dictMatchState
                        && repIndex2 < prefixLowestIndex ?
                            dictBase - dictIndexDelta + repIndex2 :
                            base + repIndex2;
                    if ( ((U32)((prefixLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
                       && (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
                        const BYTE* const repEnd2 = repIndex2 < prefixLowestIndex ? dictEnd : iend;
                        size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixLowest) + 4;
                        U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset;   /* swap offset_2 <=> offset_1 */
                        ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH);
                        hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = current2;
                        hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = current2;
                        ip += repLength2;
                        anchor = ip;
                        continue;
                    }
                    break;
                }
            }

            if (dictMode == ZSTD_noDict) {
                while ( (ip <= ilimit)
                     && ( (offset_2>0)
                        & (MEM_read32(ip) == MEM_read32(ip - offset_2)) )) {
                    /* store sequence */
                    size_t const rLength = ZSTD_count(ip+4, ip+4-offset_2, iend) + 4;
                    U32 const tmpOff = offset_2; offset_2 = offset_1; offset_1 = tmpOff;  /* swap offset_2 <=> offset_1 */
                    hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = (U32)(ip-base);
                    hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = (U32)(ip-base);
                    ZSTD_storeSeq(seqStore, 0, anchor, 0, rLength-MINMATCH);
                    ip += rLength;
                    anchor = ip;
                    continue;   /* faster when present ... (?) */
    }   }   }   }

    /* save reps for next block */
    rep[0] = offset_1 ? offset_1 : offsetSaved;
    rep[1] = offset_2 ? offset_2 : offsetSaved;

    /* Return the last literals size */
    return iend - anchor;
}


size_t ZSTD_compressBlock_doubleFast(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize)
{
    const U32 mls = ms->cParams.searchLength;
    switch(mls)
    {
    default: /* includes case 3 */
    case 4 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 4, ZSTD_noDict);
    case 5 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 5, ZSTD_noDict);
    case 6 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 6, ZSTD_noDict);
    case 7 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 7, ZSTD_noDict);
    }
}


size_t ZSTD_compressBlock_doubleFast_dictMatchState(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize)
{
    const U32 mls = ms->cParams.searchLength;
    switch(mls)
    {
    default: /* includes case 3 */
    case 4 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 4, ZSTD_dictMatchState);
    case 5 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 5, ZSTD_dictMatchState);
    case 6 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 6, ZSTD_dictMatchState);
    case 7 :
        return ZSTD_compressBlock_doubleFast_generic(ms, seqStore, rep, src, srcSize, 7, ZSTD_dictMatchState);
    }
}


static size_t ZSTD_compressBlock_doubleFast_extDict_generic(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize,
        U32 const mls /* template */)
{
    ZSTD_compressionParameters const* cParams = &ms->cParams;
    U32* const hashLong = ms->hashTable;
    U32  const hBitsL = cParams->hashLog;
    U32* const hashSmall = ms->chainTable;
    U32  const hBitsS = cParams->chainLog;
    const BYTE* const istart = (const BYTE*)src;
    const BYTE* ip = istart;
    const BYTE* anchor = istart;
    const BYTE* const iend = istart + srcSize;
    const BYTE* const ilimit = iend - 8;
    const U32   prefixStartIndex = ms->window.dictLimit;
    const BYTE* const base = ms->window.base;
    const BYTE* const prefixStart = base + prefixStartIndex;
    const U32   dictStartIndex = ms->window.lowLimit;
    const BYTE* const dictBase = ms->window.dictBase;
    const BYTE* const dictStart = dictBase + dictStartIndex;
    const BYTE* const dictEnd = dictBase + prefixStartIndex;
    U32 offset_1=rep[0], offset_2=rep[1];

    DEBUGLOG(5, "ZSTD_compressBlock_doubleFast_extDict_generic (srcSize=%zu)", srcSize);

    /* Search Loop */
    while (ip < ilimit) {  /* < instead of <=, because (ip+1) */
        const size_t hSmall = ZSTD_hashPtr(ip, hBitsS, mls);
        const U32 matchIndex = hashSmall[hSmall];
        const BYTE* const matchBase = matchIndex < prefixStartIndex ? dictBase : base;
        const BYTE* match = matchBase + matchIndex;

        const size_t hLong = ZSTD_hashPtr(ip, hBitsL, 8);
        const U32 matchLongIndex = hashLong[hLong];
        const BYTE* const matchLongBase = matchLongIndex < prefixStartIndex ? dictBase : base;
        const BYTE* matchLong = matchLongBase + matchLongIndex;

        const U32 current = (U32)(ip-base);
        const U32 repIndex = current + 1 - offset_1;   /* offset_1 expected <= current +1 */
        const BYTE* const repBase = repIndex < prefixStartIndex ? dictBase : base;
        const BYTE* const repMatch = repBase + repIndex;
        size_t mLength;
        hashSmall[hSmall] = hashLong[hLong] = current;   /* update hash table */

        if ((((U32)((prefixStartIndex-1) - repIndex) >= 3) /* intentional underflow : ensure repIndex doesn't overlap dict + prefix */
            & (repIndex > dictStartIndex))
          && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
            const BYTE* repMatchEnd = repIndex < prefixStartIndex ? dictEnd : iend;
            mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixStart) + 4;
            ip++;
            ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
        } else {
            if ((matchLongIndex > dictStartIndex) && (MEM_read64(matchLong) == MEM_read64(ip))) {
                const BYTE* const matchEnd = matchLongIndex < prefixStartIndex ? dictEnd : iend;
                const BYTE* const lowMatchPtr = matchLongIndex < prefixStartIndex ? dictStart : prefixStart;
                U32 offset;
                mLength = ZSTD_count_2segments(ip+8, matchLong+8, iend, matchEnd, prefixStart) + 8;
                offset = current - matchLongIndex;
                while (((ip>anchor) & (matchLong>lowMatchPtr)) && (ip[-1] == matchLong[-1])) { ip--; matchLong--; mLength++; }   /* catch up */
                offset_2 = offset_1;
                offset_1 = offset;
                ZSTD_storeSeq(seqStore, ip-anchor, anchor, offset + ZSTD_REP_MOVE, mLength-MINMATCH);

            } else if ((matchIndex > dictStartIndex) && (MEM_read32(match) == MEM_read32(ip))) {
                size_t const h3 = ZSTD_hashPtr(ip+1, hBitsL, 8);
                U32 const matchIndex3 = hashLong[h3];
                const BYTE* const match3Base = matchIndex3 < prefixStartIndex ? dictBase : base;
                const BYTE* match3 = match3Base + matchIndex3;
                U32 offset;
                hashLong[h3] = current + 1;
                if ( (matchIndex3 > dictStartIndex) && (MEM_read64(match3) == MEM_read64(ip+1)) ) {
                    const BYTE* const matchEnd = matchIndex3 < prefixStartIndex ? dictEnd : iend;
                    const BYTE* const lowMatchPtr = matchIndex3 < prefixStartIndex ? dictStart : prefixStart;
                    mLength = ZSTD_count_2segments(ip+9, match3+8, iend, matchEnd, prefixStart) + 8;
                    ip++;
                    offset = current+1 - matchIndex3;
                    while (((ip>anchor) & (match3>lowMatchPtr)) && (ip[-1] == match3[-1])) { ip--; match3--; mLength++; } /* catch up */
                } else {
                    const BYTE* const matchEnd = matchIndex < prefixStartIndex ? dictEnd : iend;
                    const BYTE* const lowMatchPtr = matchIndex < prefixStartIndex ? dictStart : prefixStart;
                    mLength = ZSTD_count_2segments(ip+4, match+4, iend, matchEnd, prefixStart) + 4;
                    offset = current - matchIndex;
                    while (((ip>anchor) & (match>lowMatchPtr)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; }   /* catch up */
                }
                offset_2 = offset_1;
                offset_1 = offset;
                ZSTD_storeSeq(seqStore, ip-anchor, anchor, offset + ZSTD_REP_MOVE, mLength-MINMATCH);

            } else {
                ip += ((ip-anchor) >> kSearchStrength) + 1;
                continue;
        }   }

        /* found a match : store it */
        ip += mLength;
        anchor = ip;

        if (ip <= ilimit) {
            /* Fill Table */
            hashSmall[ZSTD_hashPtr(base+current+2, hBitsS, mls)] = current+2;
            hashLong[ZSTD_hashPtr(base+current+2, hBitsL, 8)] = current+2;
            hashSmall[ZSTD_hashPtr(ip-2, hBitsS, mls)] = (U32)(ip-2-base);
            hashLong[ZSTD_hashPtr(ip-2, hBitsL, 8)] = (U32)(ip-2-base);
            /* check immediate repcode */
            while (ip <= ilimit) {
                U32 const current2 = (U32)(ip-base);
                U32 const repIndex2 = current2 - offset_2;
                const BYTE* repMatch2 = repIndex2 < prefixStartIndex ? dictBase + repIndex2 : base + repIndex2;
                if ( (((U32)((prefixStartIndex-1) - repIndex2) >= 3)   /* intentional overflow : ensure repIndex2 doesn't overlap dict + prefix */
                    & (repIndex2 > dictStartIndex))
                  && (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
                    const BYTE* const repEnd2 = repIndex2 < prefixStartIndex ? dictEnd : iend;
                    size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixStart) + 4;
                    U32 const tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset;   /* swap offset_2 <=> offset_1 */
                    ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH);
                    hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = current2;
                    hashLong[ZSTD_hashPtr(ip, hBitsL, 8)] = current2;
                    ip += repLength2;
                    anchor = ip;
                    continue;
                }
                break;
    }   }   }

    /* save reps for next block */
    rep[0] = offset_1;
    rep[1] = offset_2;

    /* Return the last literals size */
    return iend - anchor;
}


size_t ZSTD_compressBlock_doubleFast_extDict(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize)
{
    U32 const mls = ms->cParams.searchLength;
    switch(mls)
    {
    default: /* includes case 3 */
    case 4 :
        return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 4);
    case 5 :
        return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 5);
    case 6 :
        return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 6);
    case 7 :
        return ZSTD_compressBlock_doubleFast_extDict_generic(ms, seqStore, rep, src, srcSize, 7);
    }
}