/* deflate_slow.c -- compress data using the slow strategy of deflation algorithm

 *

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

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

 */

#include "zbuild.h"

#include "deflate.h"

#include "deflate_p.h"

#include "functable.h"

/* ===========================================================================

 * Same as deflate_medium, but achieves better compression. We use a lazy

 * evaluation for matches: a match is finally adopted only if there is

 * no better match at the next window position.

 */

Z_INTERNAL block_state deflate_slow(deflate_state *s, int flush) {

    Pos hash_head;           /* head of hash chain */

    int bflush;              /* set if current block must be flushed */

    int64_t dist;

    uint32_t match_len;

    match_func longest_match;

    if (s->max_chain_length <= 1024)

        longest_match = FUNCTABLE_FPTR(longest_match);

    else

        longest_match = FUNCTABLE_FPTR(longest_match_slow);

    /* Process the input block. */

    for (;;) {

        /* Make sure that we always have enough lookahead, except

         * at the end of the input file. We need STD_MAX_MATCH bytes

         * for the next match, plus WANT_MIN_MATCH bytes to insert the

         * string following the next match.

         */

        if (s->lookahead < MIN_LOOKAHEAD) {

            PREFIX(fill_window)(s);

            if (UNLIKELY(s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH)) {

                return need_more;

            }

            if (UNLIKELY(s->lookahead == 0))

                break; /* flush the current block */

        }

        /* Insert the string window[strstart .. strstart+2] in the

         * dictionary, and set hash_head to the head of the hash chain:

         */

        hash_head = 0;

        if (LIKELY(s->lookahead >= WANT_MIN_MATCH)) {

            hash_head = s->quick_insert_string(s, s->strstart);

        }

        /* Find the longest match, discarding those <= prev_length.

         */

        s->prev_match = (Pos)s->match_start;

        match_len = STD_MIN_MATCH - 1;

        dist = (int64_t)s->strstart - hash_head;

        if (dist <= MAX_DIST(s) && dist > 0 && s->prev_length < s->max_lazy_match && hash_head != 0) {

            /* To simplify the code, we prevent matches with the string

             * of window index 0 (in particular we have to avoid a match

             * of the string with itself at the start of the input file).

             */

            match_len = longest_match(s, hash_head);

            /* longest_match() sets match_start */

            if (match_len <= 5 && (s->strategy == Z_FILTERED)) {

                /* If prev_match is also WANT_MIN_MATCH, match_start is garbage

                 * but we will ignore the current match anyway.

                 */

                match_len = STD_MIN_MATCH - 1;

            }

        }

        /* If there was a match at the previous step and the current

         * match is not better, output the previous match:

         */

        if (s->prev_length >= STD_MIN_MATCH && match_len <= s->prev_length) {

            unsigned int max_insert = s->strstart + s->lookahead - STD_MIN_MATCH;

            /* Do not insert strings in hash table beyond this. */

            Assert((s->strstart-1) <= UINT16_MAX, "strstart-1 should fit in uint16_t");

            check_match(s, (Pos)(s->strstart - 1), s->prev_match, s->prev_length);

            bflush = zng_tr_tally_dist(s, s->strstart -1 - s->prev_match, s->prev_length - STD_MIN_MATCH);

            /* Insert in hash table all strings up to the end of the match.

             * strstart-1 and strstart are already inserted. If there is not

             * enough lookahead, the last two strings are not inserted in

             * the hash table.

             */

            s->prev_length -= 1;

            s->lookahead -= s->prev_length;

            unsigned int mov_fwd = s->prev_length - 1;

            if (max_insert > s->strstart) {

                unsigned int insert_cnt = mov_fwd;

                if (UNLIKELY(insert_cnt > max_insert - s->strstart))

                    insert_cnt = max_insert - s->strstart;

                s->insert_string(s, s->strstart + 1, insert_cnt);

            }

            s->prev_length = 0;

            s->match_available = 0;

            s->strstart += mov_fwd + 1;

            if (UNLIKELY(bflush))

                FLUSH_BLOCK(s, 0);

        } else if (s->match_available) {

            /* If there was no match at the previous position, output a

             * single literal. If there was a match but the current match

             * is longer, truncate the previous match to a single literal.

             */

            bflush = zng_tr_tally_lit(s, s->window[s->strstart-1]);

            if (UNLIKELY(bflush))

                FLUSH_BLOCK_ONLY(s, 0);

            s->prev_length = match_len;

            s->strstart++;

            s->lookahead--;

            if (UNLIKELY(s->strm->avail_out == 0))

                return need_more;

        } else {

            /* There is no previous match to compare with, wait for

             * the next step to decide.

             */

            s->prev_length = match_len;

            s->match_available = 1;

            s->strstart++;

            s->lookahead--;

        }

    }

    Assert(flush != Z_NO_FLUSH, "no flush?");

    if (UNLIKELY(s->match_available)) {

        Z_UNUSED(zng_tr_tally_lit(s, s->window[s->strstart-1]));

        s->match_available = 0;

    }

    s->insert = s->strstart < (STD_MIN_MATCH - 1) ? s->strstart : (STD_MIN_MATCH - 1);

    if (UNLIKELY(flush == Z_FINISH)) {

        FLUSH_BLOCK(s, 1);

        return finish_done;

    }

    if (UNLIKELY(s->sym_next))

        FLUSH_BLOCK(s, 0);

    return block_done;

}