annotate contrib/python-zstandard/zstd/compress/zstd_fast.c @ 44413:4cabeea6d214

hgext: start building a library for simple hooks

Many workflows depend on hooks to enforce certain policies, e.g. to
prevent forced pushes. The Mercurial Guide includes some cases and
Google can help finding others, but it can save users a lot of time
if hg itself has a couple of examples for further customization.

Differential Revision: https://phab.mercurial-scm.org/D6825

/*
 * 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"  /* ZSTD_hashPtr, ZSTD_count, ZSTD_storeSeq */
#include "zstd_fast.h"


void ZSTD_fillHashTable(ZSTD_matchState_t* ms,
                        const void* const end,
                        ZSTD_dictTableLoadMethod_e dtlm)
{
    const ZSTD_compressionParameters* const cParams = &ms->cParams;
    U32* const hashTable = ms->hashTable;
    U32  const hBits = cParams->hashLog;
    U32  const mls = cParams->minMatch;
    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 table.
     * Insert the other positions if their hash entry is empty.
     */
    for ( ; ip + fastHashFillStep < iend + 2; ip += fastHashFillStep) {
        U32 const current = (U32)(ip - base);
        size_t const hash0 = ZSTD_hashPtr(ip, hBits, mls);
        hashTable[hash0] = current;
        if (dtlm == ZSTD_dtlm_fast) continue;
        /* Only load extra positions for ZSTD_dtlm_full */
        {   U32 p;
            for (p = 1; p < fastHashFillStep; ++p) {
                size_t const hash = ZSTD_hashPtr(ip + p, hBits, mls);
                if (hashTable[hash] == 0) {  /* not yet filled */
                    hashTable[hash] = current + p;
    }   }   }   }
}


FORCE_INLINE_TEMPLATE size_t
ZSTD_compressBlock_fast_generic(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize,
        U32 const mls)
{
    const ZSTD_compressionParameters* const cParams = &ms->cParams;
    U32* const hashTable = ms->hashTable;
    U32 const hlog = cParams->hashLog;
    /* support stepSize of 0 */
    size_t const stepSize = cParams->targetLength + !(cParams->targetLength) + 1;
    const BYTE* const base = ms->window.base;
    const BYTE* const istart = (const BYTE*)src;
    /* We check ip0 (ip + 0) and ip1 (ip + 1) each loop */
    const BYTE* ip0 = istart;
    const BYTE* ip1;
    const BYTE* anchor = istart;
    const U32   endIndex = (U32)((size_t)(istart - base) + srcSize);
    const U32   maxDistance = 1U << cParams->windowLog;
    const U32   validStartIndex = ms->window.dictLimit;
    const U32   prefixStartIndex = (endIndex - validStartIndex > maxDistance) ? endIndex - maxDistance : validStartIndex;
    const BYTE* const prefixStart = base + prefixStartIndex;
    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;

    /* init */
    DEBUGLOG(5, "ZSTD_compressBlock_fast_generic");
    ip0 += (ip0 == prefixStart);
    ip1 = ip0 + 1;
    {   U32 const maxRep = (U32)(ip0 - prefixStart);
        if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0;
        if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0;
    }

    /* Main Search Loop */
    while (ip1 < ilimit) {   /* < instead of <=, because check at ip0+2 */
        size_t mLength;
        BYTE const* ip2 = ip0 + 2;
        size_t const h0 = ZSTD_hashPtr(ip0, hlog, mls);
        U32 const val0 = MEM_read32(ip0);
        size_t const h1 = ZSTD_hashPtr(ip1, hlog, mls);
        U32 const val1 = MEM_read32(ip1);
        U32 const current0 = (U32)(ip0-base);
        U32 const current1 = (U32)(ip1-base);
        U32 const matchIndex0 = hashTable[h0];
        U32 const matchIndex1 = hashTable[h1];
        BYTE const* repMatch = ip2-offset_1;
        const BYTE* match0 = base + matchIndex0;
        const BYTE* match1 = base + matchIndex1;
        U32 offcode;
        hashTable[h0] = current0;   /* update hash table */
        hashTable[h1] = current1;   /* update hash table */

        assert(ip0 + 1 == ip1);

        if ((offset_1 > 0) & (MEM_read32(repMatch) == MEM_read32(ip2))) {
            mLength = ip2[-1] == repMatch[-1] ? 1 : 0;
            ip0 = ip2 - mLength;
            match0 = repMatch - mLength;
            offcode = 0;
            goto _match;
        }
        if ((matchIndex0 > prefixStartIndex) && MEM_read32(match0) == val0) {
            /* found a regular match */
            goto _offset;
        }
        if ((matchIndex1 > prefixStartIndex) && MEM_read32(match1) == val1) {
            /* found a regular match after one literal */
            ip0 = ip1;
            match0 = match1;
            goto _offset;
        }
        {   size_t const step = ((size_t)(ip0-anchor) >> (kSearchStrength - 1)) + stepSize;
            assert(step >= 2);
            ip0 += step;
            ip1 += step;
            continue;
        }
_offset: /* Requires: ip0, match0 */
        /* Compute the offset code */
        offset_2 = offset_1;
        offset_1 = (U32)(ip0-match0);
        offcode = offset_1 + ZSTD_REP_MOVE;
        mLength = 0;
        /* Count the backwards match length */
        while (((ip0>anchor) & (match0>prefixStart))
             && (ip0[-1] == match0[-1])) { ip0--; match0--; mLength++; } /* catch up */

_match: /* Requires: ip0, match0, offcode */
        /* Count the forward length */
        mLength += ZSTD_count(ip0+mLength+4, match0+mLength+4, iend) + 4;
        ZSTD_storeSeq(seqStore, (size_t)(ip0-anchor), anchor, iend, offcode, mLength-MINMATCH);
        /* match found */
        ip0 += mLength;
        anchor = ip0;
        ip1 = ip0 + 1;

        if (ip0 <= ilimit) {
            /* Fill Table */
            assert(base+current0+2 > istart);  /* check base overflow */
            hashTable[ZSTD_hashPtr(base+current0+2, hlog, mls)] = current0+2;  /* here because current+2 could be > iend-8 */
            hashTable[ZSTD_hashPtr(ip0-2, hlog, mls)] = (U32)(ip0-2-base);

            while ( ((ip0 <= ilimit) & (offset_2>0))  /* offset_2==0 means offset_2 is invalidated */
                 && (MEM_read32(ip0) == MEM_read32(ip0 - offset_2)) ) {
                /* store sequence */
                size_t const rLength = ZSTD_count(ip0+4, ip0+4-offset_2, iend) + 4;
                { U32 const tmpOff = offset_2; offset_2 = offset_1; offset_1 = tmpOff; } /* swap offset_2 <=> offset_1 */
                hashTable[ZSTD_hashPtr(ip0, hlog, mls)] = (U32)(ip0-base);
                ip0 += rLength;
                ip1 = ip0 + 1;
                ZSTD_storeSeq(seqStore, 0 /*litLen*/, anchor, iend, 0 /*offCode*/, rLength-MINMATCH);
                anchor = ip0;
                continue;   /* faster when present (confirmed on gcc-8) ... (?) */
            }
        }
    }

    /* 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 (size_t)(iend - anchor);
}


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

FORCE_INLINE_TEMPLATE
size_t ZSTD_compressBlock_fast_dictMatchState_generic(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize, U32 const mls)
{
    const ZSTD_compressionParameters* const cParams = &ms->cParams;
    U32* const hashTable = ms->hashTable;
    U32 const hlog = cParams->hashLog;
    /* support stepSize of 0 */
    U32 const stepSize = cParams->targetLength + !(cParams->targetLength);
    const BYTE* const base = ms->window.base;
    const BYTE* const istart = (const BYTE*)src;
    const BYTE* ip = istart;
    const BYTE* anchor = istart;
    const U32   prefixStartIndex = ms->window.dictLimit;
    const BYTE* const prefixStart = base + prefixStartIndex;
    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 = &dms->cParams ;
    const U32* const dictHashTable = dms->hashTable;
    const U32 dictStartIndex       = dms->window.dictLimit;
    const BYTE* const dictBase     = dms->window.base;
    const BYTE* const dictStart    = dictBase + dictStartIndex;
    const BYTE* const dictEnd      = dms->window.nextSrc;
    const U32 dictIndexDelta       = prefixStartIndex - (U32)(dictEnd - dictBase);
    const U32 dictAndPrefixLength  = (U32)(ip - prefixStart + dictEnd - dictStart);
    const U32 dictHLog             = dictCParams->hashLog;

    /* if a dictionary is still attached, it necessarily means that
     * it is within window size. So we just check it. */
    const U32 maxDistance = 1U << cParams->windowLog;
    const U32 endIndex = (U32)((size_t)(ip - base) + srcSize);
    assert(endIndex - prefixStartIndex <= maxDistance);
    (void)maxDistance; (void)endIndex;   /* these variables are not used when assert() is disabled */

    /* ensure there will be no no underflow
     * when translating a dict index into a local index */
    assert(prefixStartIndex >= (U32)(dictEnd - dictBase));

    /* init */
    DEBUGLOG(5, "ZSTD_compressBlock_fast_dictMatchState_generic");
    ip += (dictAndPrefixLength == 0);
    /* 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;
        size_t const h = ZSTD_hashPtr(ip, hlog, mls);
        U32 const current = (U32)(ip-base);
        U32 const matchIndex = hashTable[h];
        const BYTE* match = base + matchIndex;
        const U32 repIndex = current + 1 - offset_1;
        const BYTE* repMatch = (repIndex < prefixStartIndex) ?
                               dictBase + (repIndex - dictIndexDelta) :
                               base + repIndex;
        hashTable[h] = current;   /* update hash table */

        if ( ((U32)((prefixStartIndex-1) - repIndex) >= 3) /* intentional underflow : ensure repIndex isn't overlapping dict + prefix */
          && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
            const BYTE* const repMatchEnd = repIndex < prefixStartIndex ? dictEnd : iend;
            mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixStart) + 4;
            ip++;
            ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, 0, mLength-MINMATCH);
        } else if ( (matchIndex <= prefixStartIndex) ) {
            size_t const dictHash = ZSTD_hashPtr(ip, dictHLog, mls);
            U32 const dictMatchIndex = dictHashTable[dictHash];
            const BYTE* dictMatch = dictBase + dictMatchIndex;
            if (dictMatchIndex <= dictStartIndex ||
                MEM_read32(dictMatch) != MEM_read32(ip)) {
                assert(stepSize >= 1);
                ip += ((ip-anchor) >> kSearchStrength) + stepSize;
                continue;
            } else {
                /* found a dict match */
                U32 const offset = (U32)(current-dictMatchIndex-dictIndexDelta);
                mLength = ZSTD_count_2segments(ip+4, dictMatch+4, iend, dictEnd, prefixStart) + 4;
                while (((ip>anchor) & (dictMatch>dictStart))
                     && (ip[-1] == dictMatch[-1])) {
                    ip--; dictMatch--; mLength++;
                } /* catch up */
                offset_2 = offset_1;
                offset_1 = offset;
                ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
            }
        } else if (MEM_read32(match) != MEM_read32(ip)) {
            /* it's not a match, and we're not going to check the dictionary */
            assert(stepSize >= 1);
            ip += ((ip-anchor) >> kSearchStrength) + stepSize;
            continue;
        } else {
            /* found a regular match */
            U32 const offset = (U32)(ip-match);
            mLength = ZSTD_count(ip+4, match+4, iend) + 4;
            while (((ip>anchor) & (match>prefixStart))
                 && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
            offset_2 = offset_1;
            offset_1 = offset;
            ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
        }

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

        if (ip <= ilimit) {
            /* Fill Table */
            assert(base+current+2 > istart);  /* check base overflow */
            hashTable[ZSTD_hashPtr(base+current+2, hlog, mls)] = current+2;  /* here because current+2 could be > iend-8 */
            hashTable[ZSTD_hashPtr(ip-2, hlog, mls)] = (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 - dictIndexDelta + repIndex2 :
                        base + repIndex2;
                if ( ((U32)((prefixStartIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
                   && (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 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset;   /* swap offset_2 <=> offset_1 */
                    ZSTD_storeSeq(seqStore, 0, anchor, iend, 0, repLength2-MINMATCH);
                    hashTable[ZSTD_hashPtr(ip, hlog, mls)] = current2;
                    ip += repLength2;
                    anchor = ip;
                    continue;
                }
                break;
            }
        }
    }

    /* 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 (size_t)(iend - anchor);
}

size_t ZSTD_compressBlock_fast_dictMatchState(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize)
{
    U32 const mls = ms->cParams.minMatch;
    assert(ms->dictMatchState != NULL);
    switch(mls)
    {
    default: /* includes case 3 */
    case 4 :
        return ZSTD_compressBlock_fast_dictMatchState_generic(ms, seqStore, rep, src, srcSize, 4);
    case 5 :
        return ZSTD_compressBlock_fast_dictMatchState_generic(ms, seqStore, rep, src, srcSize, 5);
    case 6 :
        return ZSTD_compressBlock_fast_dictMatchState_generic(ms, seqStore, rep, src, srcSize, 6);
    case 7 :
        return ZSTD_compressBlock_fast_dictMatchState_generic(ms, seqStore, rep, src, srcSize, 7);
    }
}


static size_t ZSTD_compressBlock_fast_extDict_generic(
        ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
        void const* src, size_t srcSize, U32 const mls)
{
    const ZSTD_compressionParameters* const cParams = &ms->cParams;
    U32* const hashTable = ms->hashTable;
    U32 const hlog = cParams->hashLog;
    /* support stepSize of 0 */
    U32 const stepSize = cParams->targetLength + !(cParams->targetLength);
    const BYTE* const base = ms->window.base;
    const BYTE* const dictBase = ms->window.dictBase;
    const BYTE* const istart = (const BYTE*)src;
    const BYTE* ip = istart;
    const BYTE* anchor = istart;
    const U32   endIndex = (U32)((size_t)(istart - base) + srcSize);
    const U32   lowLimit = ZSTD_getLowestMatchIndex(ms, endIndex, cParams->windowLog);
    const U32   dictStartIndex = lowLimit;
    const BYTE* const dictStart = dictBase + dictStartIndex;
    const U32   dictLimit = ms->window.dictLimit;
    const U32   prefixStartIndex = dictLimit < lowLimit ? lowLimit : dictLimit;
    const BYTE* const prefixStart = base + prefixStartIndex;
    const BYTE* const dictEnd = dictBase + prefixStartIndex;
    const BYTE* const iend = istart + srcSize;
    const BYTE* const ilimit = iend - 8;
    U32 offset_1=rep[0], offset_2=rep[1];

    DEBUGLOG(5, "ZSTD_compressBlock_fast_extDict_generic");

    /* switch to "regular" variant if extDict is invalidated due to maxDistance */
    if (prefixStartIndex == dictStartIndex)
        return ZSTD_compressBlock_fast_generic(ms, seqStore, rep, src, srcSize, mls);

    /* Search Loop */
    while (ip < ilimit) {  /* < instead of <=, because (ip+1) */
        const size_t h = ZSTD_hashPtr(ip, hlog, mls);
        const U32    matchIndex = hashTable[h];
        const BYTE* const matchBase = matchIndex < prefixStartIndex ? dictBase : base;
        const BYTE*  match = matchBase + matchIndex;
        const U32    current = (U32)(ip-base);
        const U32    repIndex = current + 1 - offset_1;
        const BYTE* const repBase = repIndex < prefixStartIndex ? dictBase : base;
        const BYTE* const repMatch = repBase + repIndex;
        hashTable[h] = current;   /* update hash table */
        assert(offset_1 <= current +1);   /* check repIndex */

        if ( (((U32)((prefixStartIndex-1) - repIndex) >= 3) /* intentional underflow */ & (repIndex > dictStartIndex))
           && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
            const BYTE* const repMatchEnd = repIndex < prefixStartIndex ? dictEnd : iend;
            size_t const rLength = ZSTD_count_2segments(ip+1 +4, repMatch +4, iend, repMatchEnd, prefixStart) + 4;
            ip++;
            ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, 0, rLength-MINMATCH);
            ip += rLength;
            anchor = ip;
        } else {
            if ( (matchIndex < dictStartIndex) ||
                 (MEM_read32(match) != MEM_read32(ip)) ) {
                assert(stepSize >= 1);
                ip += ((ip-anchor) >> kSearchStrength) + stepSize;
                continue;
            }
            {   const BYTE* const matchEnd = matchIndex < prefixStartIndex ? dictEnd : iend;
                const BYTE* const lowMatchPtr = matchIndex < prefixStartIndex ? dictStart : prefixStart;
                U32 const offset = current - matchIndex;
                size_t mLength = ZSTD_count_2segments(ip+4, match+4, iend, matchEnd, prefixStart) + 4;
                while (((ip>anchor) & (match>lowMatchPtr)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; }   /* catch up */
                offset_2 = offset_1; offset_1 = offset;  /* update offset history */
                ZSTD_storeSeq(seqStore, (size_t)(ip-anchor), anchor, iend, offset + ZSTD_REP_MOVE, mLength-MINMATCH);
                ip += mLength;
                anchor = ip;
        }   }

        if (ip <= ilimit) {
            /* Fill Table */
            hashTable[ZSTD_hashPtr(base+current+2, hlog, mls)] = current+2;
            hashTable[ZSTD_hashPtr(ip-2, hlog, mls)] = (U32)(ip-2-base);
            /* check immediate repcode */
            while (ip <= ilimit) {
                U32 const current2 = (U32)(ip-base);
                U32 const repIndex2 = current2 - offset_2;
                const BYTE* const repMatch2 = repIndex2 < prefixStartIndex ? dictBase + repIndex2 : base + repIndex2;
                if ( (((U32)((prefixStartIndex-1) - repIndex2) >= 3) & (repIndex2 > dictStartIndex))  /* intentional overflow */
                   && (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 /*litlen*/, anchor, iend, 0 /*offcode*/, repLength2-MINMATCH);
                    hashTable[ZSTD_hashPtr(ip, hlog, mls)] = 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 (size_t)(iend - anchor);
}


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