/* deflate_fast.c -- compress data using the fast 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 "zmemory.h"

#include "deflate.h"

#include "deflate_p.h"

#include "functable.h"

#include "insert_string_p.h"

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

 * Compress as much as possible from the input stream, return the current

 * block state.

 * This function does not perform lazy evaluation of matches and inserts

 * new strings in the dictionary only for unmatched strings or for short

 * matches. It is used only for the fast compression options.

 */

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

    int bflush = 0;       /* set if current block must be flushed */

    uint32_t match_len = 0;

    for (;;) {

        uint8_t lc;

        /* 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:

         */

        if (s->lookahead >= WANT_MIN_MATCH) {

#if BYTE_ORDER == LITTLE_ENDIAN

            uint32_t str_val = zng_memread_4(&s->window[s->strstart]);

#else

            uint32_t str_val = ZSWAP32(zng_memread_4(&s->window[s->strstart]));

#endif

            Pos hash_head = quick_insert_value(s, s->strstart, str_val);

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

            lc = (uint8_t)str_val;

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

             * At this point we have always match length < WANT_MIN_MATCH

             */

            if (dist <= MAX_DIST(s) && dist > 0 && 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 = FUNCTABLE_CALL(longest_match)(s, hash_head);

                /* longest_match() sets match_start */

            }

        } else {

            lc = s->window[s->strstart];

        }

        if (match_len >= WANT_MIN_MATCH) {

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

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

            check_match(s, (Pos)s->strstart, (Pos)s->match_start, match_len);

            bflush = zng_tr_tally_dist(s, s->strstart - s->match_start, match_len - STD_MIN_MATCH);

            s->lookahead -= match_len;

            /* Insert new strings in the hash table only if the match length

             * is not too large. This saves time but degrades compression.

             */

            if (match_len <= s->max_insert_length && s->lookahead >= WANT_MIN_MATCH) {

                match_len--; /* string at strstart already in table */

                s->strstart++;

                insert_string_static(s, s->strstart, match_len);

                s->strstart += match_len;

            } else {

                s->strstart += match_len;

                quick_insert_string(s, s->strstart + 2 - STD_MIN_MATCH);

                /* If lookahead < STD_MIN_MATCH, ins_h is garbage, but it does not

                 * matter since it will be recomputed at next deflate call.

                 */

            }

            match_len = 0;

        } else {

            /* No match, output a literal byte */

            bflush = zng_tr_tally_lit(s, lc);

            s->lookahead--;

            s->strstart++;

        }

        if (UNLIKELY(bflush))

            FLUSH_BLOCK(s, 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;

}