/* match_tpl.h -- find longest match template for compare256 variants

 *

 * Copyright (C) 1995-2024 Jean-loup Gailly and Mark Adler

 * For conditions of distribution and use, see copyright notice in zlib.h

 *

 * Portions copyright (C) 2014-2021 Konstantin Nosov

 *  Fast-zlib optimized longest_match

 *  https://github.com/gildor2/fast_zlib

 */

#include "insert_string_p.h"

#define EARLY_EXIT_TRIGGER_LEVEL 5

#define GOTO_NEXT_CHAIN \

    if (--chain_length && (cur_match = prev[cur_match & wmask]) > limit) \

        continue; \

    return best_len;

/* Set match_start to the longest match starting at the given string and

 * return its length. Matches shorter or equal to prev_length are discarded,

 * in which case the result is equal to prev_length and match_start is garbage.

 *

 * IN assertions: cur_match is the head of the hash chain for the current

 * string (strstart) and its distance is <= MAX_DIST, and prev_length >=1

 * OUT assertion: the match length is not greater than s->lookahead

 *

 * The LONGEST_MATCH_SLOW variant spends more time to attempt to find longer

 * matches once a match has already been found.

 */

Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, uint32_t cur_match) {

    const unsigned wmask = W_MASK(s);

    unsigned int strstart = s->strstart;

    const unsigned char *window = s->window;

    const Pos *prev = s->prev;

#ifdef LONGEST_MATCH_SLOW

    const Pos *head = s->head;

#endif

    const unsigned char *scan;

    const unsigned char *mbase_start = window;

    const unsigned char *mbase_end;

    uint32_t limit;

#ifdef LONGEST_MATCH_SLOW

    uint32_t limit_base;

#else

    int32_t early_exit;

#endif

    uint32_t chain_length = s->max_chain_length;

    uint32_t nice_match = (uint32_t)s->nice_match;

    uint32_t best_len, offset;

    uint32_t lookahead = s->lookahead;

    uint32_t match_offset = 0;

    uint64_t scan_start;

    uint64_t scan_end;

    /* The code is optimized for STD_MAX_MATCH-2 multiple of 16. */

    Assert(STD_MAX_MATCH == 258, "Code too clever");

    scan = window + strstart;

    best_len = s->prev_length ? s->prev_length : STD_MIN_MATCH-1;

    /* Calculate read offset which should only extend an extra byte

     * to find the next best match length.

     */

    offset = best_len-1;

    if (best_len >= sizeof(uint32_t)) {

        offset -= 2;

        if (best_len >= sizeof(uint64_t))

            offset -= 4;

    }

    scan_start = zng_memread_8(scan);

    scan_end = zng_memread_8(scan+offset);

    mbase_end  = (mbase_start+offset);

    /* Do not waste too much time if we already have a good match */

    if (best_len >= s->good_match)

        chain_length >>= 2;

    /* Stop when cur_match becomes <= limit. To simplify the code,

     * we prevent matches with the string of window index 0

     */

    limit = strstart > MAX_DIST(s) ? (strstart - MAX_DIST(s)) : 0;

#ifdef LONGEST_MATCH_SLOW

    limit_base = limit;

    if (best_len >= STD_MIN_MATCH) {

        /* We're continuing search (lazy evaluation). */

        uint32_t hash;

        uint32_t pos;

        /* Find a most distant chain starting from scan with index=1 (index=0 corresponds

         * to cur_match). We cannot use s->prev[strstart+1,...] immediately, because

         * these strings are not yet inserted into the hash table.

         */

        // use update_hash_roll for deflate_slow

        hash = update_hash_roll(0, scan[1]);

        hash = update_hash_roll(hash, scan[2]);

        for (uint32_t i = 3; i <= best_len; i++) {

            // use update_hash_roll for deflate_slow

            hash = update_hash_roll(hash, scan[i]);

            /* If we're starting with best_len >= 3, we can use offset search. */

            pos = head[hash];

            if (pos < cur_match) {

                match_offset = i - 2;

                cur_match = pos;

            }

        }

        /* Update offset-dependent variables */

        limit = limit_base+match_offset;

        if (cur_match <= limit)

            goto break_matching;

        mbase_start -= match_offset;

        mbase_end -= match_offset;

    }

#else

    early_exit = s->level < EARLY_EXIT_TRIGGER_LEVEL;

#endif

    Assert((unsigned long)strstart <= s->window_size - MIN_LOOKAHEAD, "need lookahead");

    for (;;) {

        if (cur_match >= strstart)

            break;

        /* Skip to next match if the match length cannot increase or if the match length is

         * less than 2. Note that the checks below for insufficient lookahead only occur

         * occasionally for performance reasons.

         * Therefore uninitialized memory will be accessed and conditional jumps will be made

         * that depend on those values. However the length of the match is limited to the

         * lookahead, so the output of deflate is not affected by the uninitialized values.

         */

        if (best_len < sizeof(uint32_t)) {

            for (;;) {

                if (zng_memcmp_2(mbase_end+cur_match, &scan_end) == 0 &&

                    zng_memcmp_2(mbase_start+cur_match, &scan_start) == 0)

                    break;

                GOTO_NEXT_CHAIN;

            }

        } else if (best_len >= sizeof(uint64_t)) {

            for (;;) {

                if (zng_memcmp_8(mbase_end+cur_match, &scan_end) == 0 &&

                    zng_memcmp_8(mbase_start+cur_match, &scan_start) == 0)

                    break;

                GOTO_NEXT_CHAIN;

            }

        } else {

            for (;;) {

                if (zng_memcmp_4(mbase_end+cur_match, &scan_end) == 0 &&

                    zng_memcmp_4(mbase_start+cur_match, &scan_start) == 0)

                    break;

                GOTO_NEXT_CHAIN;

            }

        }

        uint32_t len = COMPARE256(scan+2, mbase_start+cur_match+2) + 2;

        Assert(scan+len <= window+(unsigned)(s->window_size-1), "wild scan");

        if (len > best_len) {

            uint32_t match_start = cur_match - match_offset;

            s->match_start = match_start;

            /* Do not look for matches beyond the end of the input. */

            if (len > lookahead)

                return lookahead;

            if (len >= nice_match)

                return len;

            best_len = len;

            offset = best_len-1;

            if (best_len >= sizeof(uint32_t)) {

                offset -= 2;

                if (best_len >= sizeof(uint64_t))

                    offset -= 4;

            }

            scan_end = zng_memread_8(scan+offset);

#ifdef LONGEST_MATCH_SLOW

            /* Look for a better string offset */

            if (UNLIKELY(len > STD_MIN_MATCH && match_start + len < strstart)) {

                const unsigned char *scan_endstr;

                uint32_t hash;

                uint32_t pos, next_pos;

                /* Go back to offset 0 */

                cur_match -= match_offset;

                match_offset = 0;

                next_pos = cur_match;

                for (uint32_t i = 0; i <= len - STD_MIN_MATCH; i++) {

                    pos = prev[(cur_match + i) & wmask];

                    if (pos < next_pos) {

                        /* Hash chain is more distant, use it */

                        if (pos <= limit_base + i)

                            goto break_matching;

                        next_pos = pos;

                        match_offset = i;

                    }

                }

                /* Switch cur_match to next_pos chain */

                cur_match = next_pos;

                /* Try hash head at len-(STD_MIN_MATCH-1) position to see if we could get

                 * a better cur_match at the end of string. Using (STD_MIN_MATCH-1) lets

                 * us include one more byte into hash - the byte which will be checked

                 * in main loop now, and which allows to grow match by 1.

                 */

                scan_endstr = scan + len - (STD_MIN_MATCH+1);

                // use update_hash_roll for deflate_slow

                hash = update_hash_roll(0, scan_endstr[0]);

                hash = update_hash_roll(hash, scan_endstr[1]);

                hash = update_hash_roll(hash, scan_endstr[2]);

                pos = head[hash];

                if (pos < cur_match) {

                    match_offset = len - (STD_MIN_MATCH+1);

                    if (pos <= limit_base + match_offset)

                        goto break_matching;

                    cur_match = pos;

                }

                /* Update offset-dependent variables */

                limit = limit_base+match_offset;

                mbase_start = window-match_offset;

                mbase_end = (mbase_start+offset);

                continue;

            }

#endif

            mbase_end = (mbase_start+offset);

        }

#ifndef LONGEST_MATCH_SLOW

        else if (UNLIKELY(early_exit)) {

            /* The probability of finding a match later if we here is pretty low, so for

             * performance it's best to outright stop here for the lower compression levels

             */

            break;

        }

#endif

        GOTO_NEXT_CHAIN;

    }

    return best_len;

#ifdef LONGEST_MATCH_SLOW

break_matching:

    if (best_len < lookahead)

        return best_len;

    return lookahead;

#endif

}

Unexecuted instantiation: longest_match_sse2

Unexecuted instantiation: longest_match_slow_sse2

Unexecuted instantiation: longest_match_avx2

Unexecuted instantiation: longest_match_slow_avx2

Unexecuted instantiation: longest_match_avx512

Unexecuted instantiation: longest_match_slow_avx512

#undef LONGEST_MATCH_SLOW

#undef LONGEST_MATCH