opencv

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/* deflate_slow.c -- compress data using the slow strategy of deflation algorithm
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 *
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 * Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
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 * For conditions of distribution and use, see copyright notice in zlib.h
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 */
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#include "zbuild.h"
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#include "deflate.h"
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#include "deflate_p.h"
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#include "functable.h"
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/* ===========================================================================
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 * Same as deflate_medium, but achieves better compression. We use a lazy
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 * evaluation for matches: a match is finally adopted only if there is
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 * no better match at the next window position.
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 */
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Z_INTERNAL block_state deflate_slow(deflate_state *s, int flush) {
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    Pos hash_head;           /* head of hash chain */
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    int bflush;              /* set if current block must be flushed */
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    int64_t dist;
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    uint32_t match_len;
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    match_func *longest_match;
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    if (s->max_chain_length <= 1024)
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        longest_match = &functable.longest_match;
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    else
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        longest_match = &functable.longest_match_slow;
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    /* Process the input block. */
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    for (;;) {
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        /* Make sure that we always have enough lookahead, except
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         * at the end of the input file. We need STD_MAX_MATCH bytes
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         * for the next match, plus WANT_MIN_MATCH bytes to insert the
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         * string following the next match.
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         */
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        if (s->lookahead < MIN_LOOKAHEAD) {
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            PREFIX(fill_window)(s);
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            if (UNLIKELY(s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH)) {
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                return need_more;
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            }
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            if (UNLIKELY(s->lookahead == 0))
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                break; /* flush the current block */
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        }
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        /* Insert the string window[strstart .. strstart+2] in the
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         * dictionary, and set hash_head to the head of the hash chain:
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         */
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        hash_head = 0;
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        if (LIKELY(s->lookahead >= WANT_MIN_MATCH)) {
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            hash_head = s->quick_insert_string(s, s->strstart);
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        }
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        /* Find the longest match, discarding those <= prev_length.
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         */
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        s->prev_match = (Pos)s->match_start;
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        match_len = STD_MIN_MATCH - 1;
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        dist = (int64_t)s->strstart - hash_head;
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        if (dist <= MAX_DIST(s) && dist > 0 && s->prev_length < s->max_lazy_match && hash_head != 0) {
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            /* To simplify the code, we prevent matches with the string
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             * of window index 0 (in particular we have to avoid a match
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             * of the string with itself at the start of the input file).
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             */
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            match_len = (*longest_match)(s, hash_head);
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            /* longest_match() sets match_start */
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            if (match_len <= 5 && (s->strategy == Z_FILTERED)) {
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                /* If prev_match is also WANT_MIN_MATCH, match_start is garbage
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                 * but we will ignore the current match anyway.
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                 */
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                match_len = STD_MIN_MATCH - 1;
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            }
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        }
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        /* If there was a match at the previous step and the current
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         * match is not better, output the previous match:
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         */
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        if (s->prev_length >= STD_MIN_MATCH && match_len <= s->prev_length) {
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            unsigned int max_insert = s->strstart + s->lookahead - STD_MIN_MATCH;
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            /* Do not insert strings in hash table beyond this. */
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            check_match(s, s->strstart-1, s->prev_match, s->prev_length);
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            bflush = zng_tr_tally_dist(s, s->strstart -1 - s->prev_match, s->prev_length - STD_MIN_MATCH);
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            /* Insert in hash table all strings up to the end of the match.
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             * strstart-1 and strstart are already inserted. If there is not
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             * enough lookahead, the last two strings are not inserted in
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             * the hash table.
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             */
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            s->prev_length -= 1;
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            s->lookahead -= s->prev_length;
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            unsigned int mov_fwd = s->prev_length - 1;
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            if (max_insert > s->strstart) {
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                unsigned int insert_cnt = mov_fwd;
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                if (UNLIKELY(insert_cnt > max_insert - s->strstart))
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                    insert_cnt = max_insert - s->strstart;
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                s->insert_string(s, s->strstart + 1, insert_cnt);
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            }
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            s->prev_length = 0;
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            s->match_available = 0;
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            s->strstart += mov_fwd + 1;
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            if (UNLIKELY(bflush))
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                FLUSH_BLOCK(s, 0);
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        } else if (s->match_available) {
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            /* If there was no match at the previous position, output a
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             * single literal. If there was a match but the current match
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             * is longer, truncate the previous match to a single literal.
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             */
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            bflush = zng_tr_tally_lit(s, s->window[s->strstart-1]);
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            if (UNLIKELY(bflush))
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                FLUSH_BLOCK_ONLY(s, 0);
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            s->prev_length = match_len;
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            s->strstart++;
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            s->lookahead--;
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            if (UNLIKELY(s->strm->avail_out == 0))
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                return need_more;
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        } else {
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            /* There is no previous match to compare with, wait for
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             * the next step to decide.
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             */
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            s->prev_length = match_len;
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            s->match_available = 1;
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            s->strstart++;
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            s->lookahead--;
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        }
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    }
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    Assert(flush != Z_NO_FLUSH, "no flush?");
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    if (UNLIKELY(s->match_available)) {
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        (void) zng_tr_tally_lit(s, s->window[s->strstart-1]);
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        s->match_available = 0;
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    }
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    s->insert = s->strstart < (STD_MIN_MATCH - 1) ? s->strstart : (STD_MIN_MATCH - 1);
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    if (UNLIKELY(flush == Z_FINISH)) {
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        FLUSH_BLOCK(s, 1);
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        return finish_done;
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    }
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    if (UNLIKELY(s->sym_next))
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        FLUSH_BLOCK(s, 0);
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    return block_done;
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}
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