zlib.c

经典的ppp程序

    if (strm->next_in == Z_NULL && strm->avail_in != 0) {
        ERR_RETURN(strm, Z_STREAM_ERROR);
    }
    if (strm->avail_out == 0) ERR_RETURN(strm, Z_BUF_ERROR);

    state->strm = strm; /* just in case */

    /* Write the zlib header */
    if (state->status == INIT_STATE) {

        uInt header = (DEFLATED + ((state->w_bits-8)<<4)) << 8;
        uInt level_flags = (state->level-1) >> 1;

        if (level_flags > 3) level_flags = 3;
        header |= (level_flags << 6);
        header += 31 - (header % 31);

        state->status = BUSY_STATE;
        putShortMSB(state, header);
    }

    /* Flush as much pending output as possible */
    if (state->pending != 0) {
        flush_pending(strm);
        if (strm->avail_out == 0) return Z_OK;
    }

    /* If we came back in here to get the last output from
     * a previous flush, we're done for now.
     */
    if (state->status == FLUSH_STATE) {
	state->status = BUSY_STATE;
	if (flush != Z_NO_FLUSH && flush != Z_FINISH)
	    return Z_OK;
    }

    /* User must not provide more input after the first FINISH: */
    if (state->status == FINISH_STATE && strm->avail_in != 0) {
        ERR_RETURN(strm, Z_BUF_ERROR);
    }

    /* Start a new block or continue the current one.
     */
    if (strm->avail_in != 0 || state->lookahead != 0 ||
        (flush == Z_FINISH && state->status != FINISH_STATE)) {
        int quit;

        if (flush == Z_FINISH) {
            state->status = FINISH_STATE;
        }
        if (state->level <= 3) {
            quit = deflate_fast(state, flush);
        } else {
            quit = deflate_slow(state, flush);
        }
        if (quit || strm->avail_out == 0)
	    return Z_OK;
        /* If flush != Z_NO_FLUSH && avail_out == 0, the next call
         * of deflate should use the same flush parameter to make sure
         * that the flush is complete. So we don't have to output an
         * empty block here, this will be done at next call. This also
         * ensures that for a very small output buffer, we emit at most
         * one empty block.
         */
    }

    /* If a flush was requested, we have a little more to output now. */
    if (flush != Z_NO_FLUSH && flush != Z_FINISH
	&& state->status != FINISH_STATE) {
	switch (flush) {
	case Z_PARTIAL_FLUSH:
	    ct_align(state);
	    break;
	case Z_PACKET_FLUSH:
	    /* Output just the 3-bit `stored' block type value,
	       but not a zero length. */
	    ct_stored_type_only(state);
	    break;
	default:
	    ct_stored_block(state, (char*)0, 0L, 0);
	    /* For a full flush, this empty block will be recognized
	     * as a special marker by inflate_sync().
	     */
	    if (flush == Z_FULL_FLUSH) {
		CLEAR_HASH(state);             /* forget history */
	    }
	}
	flush_pending(strm);
	if (strm->avail_out == 0) {
	    /* We'll have to come back to get the rest of the output;
	     * this ensures we don't output a second zero-length stored
	     * block (or whatever).
	     */
	    state->status = FLUSH_STATE;
	    return Z_OK;
	}
    }

    Assert(strm->avail_out > 0, "bug2");

    if (flush != Z_FINISH) return Z_OK;
    if (state->noheader) return Z_STREAM_END;

    /* Write the zlib trailer (adler32) */
    putShortMSB(state, (uInt)(state->adler >> 16));
    putShortMSB(state, (uInt)(state->adler & 0xffff));
    flush_pending(strm);
    /* If avail_out is zero, the application will call deflate again
     * to flush the rest.
     */
    state->noheader = -1; /* write the trailer only once! */
    return state->pending != 0 ? Z_OK : Z_STREAM_END;
}

/* ========================================================================= */
int deflateEnd (strm)
    z_stream *strm;
{
    deflate_state *state = (deflate_state *) strm->state;

    if (strm == Z_NULL || state == Z_NULL) return Z_STREAM_ERROR;

    TRY_FREE(strm, state->window, state->w_size * 2 * sizeof(Byte));
    TRY_FREE(strm, state->prev, state->w_size * sizeof(Pos));
    TRY_FREE(strm, state->head, state->hash_size * sizeof(Pos));
    TRY_FREE(strm, state->pending_buf, state->lit_bufsize * 2 * sizeof(ush));

    ZFREE(strm, state, sizeof(deflate_state));
    strm->state = Z_NULL;

    return Z_OK;
}

/* ===========================================================================
 * Read a new buffer from the current input stream, update the adler32
 * and total number of bytes read.
 */
local int read_buf(strm, buf, size)
    z_stream *strm;
    charf *buf;
    unsigned size;
{
    unsigned len = strm->avail_in;
    deflate_state *state = (deflate_state *) strm->state;

    if (len > size) len = size;
    if (len == 0) return 0;

    strm->avail_in  -= len;

    if (!state->noheader) {
        state->adler = adler32(state->adler, strm->next_in, len);
    }
    zmemcpy(buf, strm->next_in, len);
    strm->next_in  += len;
    strm->total_in += len;

    return (int)len;
}

/* ===========================================================================
 * Initialize the "longest match" routines for a new zlib stream
 */
local void lm_init (s)
    deflate_state *s;
{
    s->window_size = (ulg)2L*s->w_size;

    CLEAR_HASH(s);

    /* Set the default configuration parameters:
     */
    s->max_lazy_match   = configuration_table[s->level].max_lazy;
    s->good_match       = configuration_table[s->level].good_length;
    s->nice_match       = configuration_table[s->level].nice_length;
    s->max_chain_length = configuration_table[s->level].max_chain;

    s->strstart = 0;
    s->block_start = 0L;
    s->lookahead = 0;
    s->match_length = MIN_MATCH-1;
    s->match_available = 0;
    s->ins_h = 0;
#ifdef ASMV
    match_init(); /* initialize the asm code */
#endif
}

/* ===========================================================================
 * 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
 */
#ifndef ASMV
/* For 80x86 and 680x0, an optimized version will be provided in match.asm or
 * match.S. The code will be functionally equivalent.
 */
local int longest_match(s, cur_match)
    deflate_state *s;
    IPos cur_match;                             /* current match */
{
    unsigned chain_length = s->max_chain_length;/* max hash chain length */
    register Bytef *scan = s->window + s->strstart; /* current string */
    register Bytef *match;                       /* matched string */
    register int len;                           /* length of current match */
    int best_len = s->prev_length;              /* best match length so far */
    IPos limit = s->strstart > (IPos)MAX_DIST(s) ?
        s->strstart - (IPos)MAX_DIST(s) : NIL;
    /* Stop when cur_match becomes <= limit. To simplify the code,
     * we prevent matches with the string of window index 0.
     */
    Posf *prev = s->prev;
    uInt wmask = s->w_mask;

#ifdef UNALIGNED_OK
    /* Compare two bytes at a time. Note: this is not always beneficial.
     * Try with and without -DUNALIGNED_OK to check.
     */
    register Bytef *strend = s->window + s->strstart + MAX_MATCH - 1;
    register ush scan_start = *(ushf*)scan;
    register ush scan_end   = *(ushf*)(scan+best_len-1);
#else
    register Bytef *strend = s->window + s->strstart + MAX_MATCH;
    register Byte scan_end1  = scan[best_len-1];
    register Byte scan_end   = scan[best_len];
#endif

    /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
     * It is easy to get rid of this optimization if necessary.
     */
    Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever");

    /* Do not waste too much time if we already have a good match: */
    if (s->prev_length >= s->good_match) {
        chain_length >>= 2;
    }
    Assert((ulg)s->strstart <= s->window_size-MIN_LOOKAHEAD, "need lookahead");

    do {
        Assert(cur_match < s->strstart, "no future");
        match = s->window + cur_match;

        /* Skip to next match if the match length cannot increase
         * or if the match length is less than 2:
         */
#if (defined(UNALIGNED_OK) && MAX_MATCH == 258)
        /* This code assumes sizeof(unsigned short) == 2. Do not use
         * UNALIGNED_OK if your compiler uses a different size.
         */
        if (*(ushf*)(match+best_len-1) != scan_end ||
            *(ushf*)match != scan_start) continue;

        /* It is not necessary to compare scan[2] and match[2] since they are
         * always equal when the other bytes match, given that the hash keys
         * are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at
         * strstart+3, +5, ... up to strstart+257. We check for insufficient
         * lookahead only every 4th comparison; the 128th check will be made
         * at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is
         * necessary to put more guard bytes at the end of the window, or
         * to check more often for insufficient lookahead.
         */
        Assert(scan[2] == match[2], "scan[2]?");
        scan++, match++;
        do {
        } while (*(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
                 *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
                 *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
                 *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
                 scan < strend);
        /* The funny "do {}" generates better code on most compilers */

        /* Here, scan <= window+strstart+257 */
        Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
        if (*scan == *match) scan++;

        len = (MAX_MATCH - 1) - (int)(strend-scan);
        scan = strend - (MAX_MATCH-1);

#else /* UNALIGNED_OK */

        if (match[best_len]   != scan_end  ||
            match[best_len-1] != scan_end1 ||
            *match            != *scan     ||
            *++match          != scan[1])      continue;

        /* The check at best_len-1 can be removed because it will be made
         * again later. (This heuristic is not always a win.)
         * It is not necessary to compare scan[2] and match[2] since they
         * are always equal when the other bytes match, given that
         * the hash keys are equal and that HASH_BITS >= 8.
         */
        scan += 2, match++;
        Assert(*scan == *match, "match[2]?");

        /* We check for insufficient lookahead only every 8th comparison;
         * the 256th check will be made at strstart+258.
         */
        do {
        } while (*++scan == *++match && *++scan == *++match &&
                 *++scan == *++match && *++scan == *++match &&
                 *++scan == *++match && *++scan == *++match &&
                 *++scan == *++match && *++scan == *++match &&
                 scan < strend);

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

        len = MAX_MATCH - (int)(strend - scan);
        scan = strend - MAX_MATCH;

#endif /* UNALIGNED_OK */

        if (len > best_len) {
            s->match_start = cur_match;
            best_len = len;
            if (len >= s->nice_match) break;
#ifdef UNALIGNED_OK
            scan_end = *(ushf*)(scan+best_len-1);
#else
            scan_end1  = scan[best_len-1];
            scan_end   = scan[best_len];
#endif
        }
    } while ((cur_match = prev[cur_match & wmask]) > limit
             && --chain_length != 0);

    return best_len;
}
#endif /* ASMV */

#ifdef DEBUG_ZLIB
/* ===========================================================================
 * Check that the match at match_start is indeed a match.
 */
local void check_match(s, start, match, length)
    deflate_state *s;
    IPos start, match;
    int length;
{
    /* check that the match is indeed a match */
    if (memcmp((charf *)s->window + match,
                (charf *)s->window + start, length) != EQUAL) {
        fprintf(stderr,
            " start %u, match %u, length %d\n",
            start, match, length);
        do { fprintf(stderr, "%c%c", s->window[match++],
                     s->window[start++]); } while (--length != 0);
        z_error("invalid match");
    }
    if (verbose > 1) {
        fprintf(stderr,"\\[%d,%d]", start-match, length);
        do { putc(s->window[start++], stderr); } while (--length != 0);
    }
}
#else
#  define check_match(s, start, match, length)
#endif

/* ===========================================================================
 * Fill the window when the lookahead becomes insufficient.
 * Updates strstart and lookahead.
 *
 * IN assertion: lookahead < MIN_LOOKAHEAD
 * OUT assertions: strstart <= window_size-MIN_LOOKAHEAD
 *    At least one byte has been read, or avail_in == 0; reads are
 *    performed for at least two bytes (required for the zip translate_eol
 *    option -- not supported here).