在有限窗口中查找重复串，并比较相邻匹配

159#else160#define INSERT_STRING(s, str, match_head) \161   (UPDATE_HASH(s, s->ins_h, s->window[(str) + (MIN_MATCH-1)]), \162    match_head = s->prev[(str) & s->w_mask] = s->head[s->ins_h], \163    s->head[s->ins_h] = (Pos)(str))164#endif

1390local uInt longest_match(deflate_state *s, IPos cur_match) {1391    unsigned chain_length = s->max_chain_length;/* max hash chain length */1392    Bytef *scan = s->window + s->strstart;      /* current string */1393    Bytef *match;                               /* matched string */1394    int len;                                    /* length of current match */1395    int best_len = (int)s->prev_length;         /* best match length so far */1396    int nice_match = s->nice_match;             /* stop if match long enough */1397    IPos limit = s->strstart > (IPos)MAX_DIST(s) ?1398        s->strstart - (IPos)MAX_DIST(s) : NIL;1399    /* Stop when cur_match becomes <= limit. To simplify the code,1400     * we prevent matches with the string of window index 0.1401     */1402    Posf *prev = s->prev;1403    uInt wmask = s->w_mask;

1515        if (len > best_len) {1516            s->match_start = cur_match;1517            best_len = len;1518            if (len >= nice_match) break;1519#ifdef UNALIGNED_OK1520            scan_end = *(ushf*)(scan + best_len - 1);1521#else1522            scan_end1  = scan[best_len - 1];1523            scan_end   = scan[best_len];1524#endif1525        }1526    } while ((cur_match = prev[cur_match & wmask]) > limit1527             && --chain_length != 0);15281529    if ((uInt)best_len <= s->lookahead) return (uInt)best_len;1530    return s->lookahead;

1976        /* Insert the string window[strstart .. strstart + 2] in the1977         * dictionary, and set hash_head to the head of the hash chain:1978         */1979        hash_head = NIL;1980        if (s->lookahead >= MIN_MATCH) {1981            INSERT_STRING(s, s->strstart, hash_head);1982        }19831984        /* Find the longest match, discarding those <= prev_length.1985         */1986        s->prev_length = s->match_length, s->prev_match = s->match_start;1987        s->match_length = MIN_MATCH-1;19881989        if (hash_head != NIL && s->prev_length < s->max_lazy_match &&1990            s->strstart - hash_head <= MAX_DIST(s)) {1991            /* To simplify the code, we prevent matches with the string1992             * of window index 0 (in particular we have to avoid a match1993             * of the string with itself at the start of the input file).1994             */1995            s->match_length = longest_match (s, hash_head);

2011        /* If there was a match at the previous step and the current2012         * match is not better, output the previous match:2013         */2014        if (s->prev_length >= MIN_MATCH && s->match_length <= s->prev_length) {2015            uInt max_insert = s->strstart + s->lookahead - MIN_MATCH;2016            /* Do not insert strings in hash table beyond this. */20172018            check_match(s, s->strstart - 1, s->prev_match, (int)s->prev_length);20192020            _tr_tally_dist(s, s->strstart - 1 - s->prev_match,2021                           s->prev_length - MIN_MATCH, bflush);