deflate.c

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 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree. Updates opt_len to take into account the repeat
 * counts. (The contribution of the bit length codes will be added later
 * during the construction of bl_tree.)
 */
local void scan_tree(
    DeflateHandler encoder,
    ct_data near *tree,	/* the tree to be scanned */
    int max_code)	/* and its largest code of non zero frequency */
{
    int n;			/* iterates over all tree elements */
    int prevlen = -1;		/* last emitted length */
    int curlen;			/* length of current code */
    int nextlen = tree[0].Len;	/* length of next code */
    int count = 0;		/* repeat count of the current code */
    int max_count = 7;		/* max repeat count */
    int min_count = 4;		/* min repeat count */

    if(nextlen == 0)
	max_count = 138, min_count = 3;
    tree[max_code+1].Len = (ush)0xffff; /* guard */

    for(n = 0; n <= max_code; n++) {
	curlen = nextlen; nextlen = tree[n+1].Len;
	if(++count < max_count && curlen == nextlen) {
	    continue;
	} else if(count < min_count) {
	    encoder->bl_tree[curlen].Freq += count;
	} else if(curlen != 0) {
	    if(curlen != prevlen)
		encoder->bl_tree[curlen].Freq++;
	    encoder->bl_tree[REP_3_6].Freq++;
	} else if(count <= 10) {
	    encoder->bl_tree[REPZ_3_10].Freq++;
	} else {
	    encoder->bl_tree[REPZ_11_138].Freq++;
	}
	count = 0; prevlen = curlen;
	if(nextlen == 0) {
	    max_count = 138, min_count = 3;
	} else if(curlen == nextlen) {
	    max_count = 6, min_count = 3;
	} else {
	    max_count = 7, min_count = 4;
	}
    }
}

/* ===========================================================================
 * Send a literal or distance tree in compressed form, using the codes in
 * bl_tree.
 */
local void send_tree(
    DeflateHandler encoder,
    ct_data near *tree,	/* the tree to be scanned */
    int max_code)	/* and its largest code of non zero frequency */
{
    int n;			/* iterates over all tree elements */
    int prevlen = -1;		/* last emitted length */
    int curlen;			/* length of current code */
    int nextlen = tree[0].Len;	/* length of next code */
    int count = 0;		/* repeat count of the current code */
    int max_count = 7;		/* max repeat count */
    int min_count = 4;		/* min repeat count */

    /* tree[max_code+1].Len = -1; */  /* guard already set */
    if(nextlen == 0) max_count = 138, min_count = 3;

    for(n = 0; n <= max_code; n++) {
	curlen = nextlen; nextlen = tree[n+1].Len;
	if(++count < max_count && curlen == nextlen) {
	    continue;
	} else if(count < min_count) {
	    do { SEND_CODE(curlen, encoder->bl_tree); } while(--count != 0);

	} else if(curlen != 0) {
	    if(curlen != prevlen) {
		SEND_CODE(curlen, encoder->bl_tree);
		count--;
	    }
	    Assert(count >= 3 && count <= 6, " 3_6?");
	    SEND_CODE(REP_3_6, encoder->bl_tree);
	    send_bits(encoder, count-3, 2);

	} else if(count <= 10) {
	    SEND_CODE(REPZ_3_10, encoder->bl_tree);
	    send_bits(encoder, count-3, 3);

	} else {
	    SEND_CODE(REPZ_11_138, encoder->bl_tree);
	    send_bits(encoder, count-11, 7);
	}
	count = 0; prevlen = curlen;
	if(nextlen == 0) {
	    max_count = 138, min_count = 3;
	} else if(curlen == nextlen) {
	    max_count = 6, min_count = 3;
	} else {
	    max_count = 7, min_count = 4;
	}
    }
}

/* ===========================================================================
 * Construct the Huffman tree for the bit lengths and return the index in
 * bl_order of the last bit length code to send.
 */
local int build_bl_tree(DeflateHandler encoder)
{
    int max_blindex;  /* index of last bit length code of non zero freq */

    /* Determine the bit length frequencies for literal and distance trees */
    scan_tree(encoder,
	      (ct_data near *)encoder->dyn_ltree, encoder->l_desc.max_code);
    scan_tree(encoder,
	      (ct_data near *)encoder->dyn_dtree, encoder->d_desc.max_code);

    /* Build the bit length tree: */
    build_tree(encoder, (tree_desc near *)(&encoder->bl_desc));
    /* opt_len now includes the length of the tree representations, except
     * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
     */

    /* Determine the number of bit length codes to send. The pkzip format
     * requires that at least 4 bit length codes be sent. (appnote.txt says
     * 3 but the actual value used is 4.)
     */
    for(max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
	if(encoder->bl_tree[bl_order[max_blindex]].Len != 0) break;
    }
    /* Update opt_len to include the bit length tree and counts */
    encoder->opt_len += 3*(max_blindex+1) + 5+5+4;
    Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",
	    encoder->opt_len, encoder->static_len));

    return max_blindex;
}

/* ===========================================================================
 * Send the header for a block using dynamic Huffman trees: the counts, the
 * lengths of the bit length codes, the literal tree and the distance tree.
 * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
 */
local void send_all_trees(
    DeflateHandler encoder,
    int lcodes, int dcodes, int blcodes) /* number of codes for each tree */
{
    int rank; /* index in bl_order */

    Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
    Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
	    "too many codes");
    Tracev((stderr, "\nbl counts: "));
    send_bits(encoder, lcodes-257, 5); /* not +255 as stated in appnote.txt */
    send_bits(encoder, dcodes-1,   5);
    send_bits(encoder, blcodes-4,  4); /* not -3 as stated in appnote.txt */
    for(rank = 0; rank < blcodes; rank++) {
	Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
	send_bits(encoder, encoder->bl_tree[bl_order[rank]].Len, 3);
    }

    /* send the literal tree */
    send_tree(encoder, (ct_data near *)encoder->dyn_ltree,lcodes-1);

    /* send the distance tree */
    send_tree(encoder, (ct_data near *)encoder->dyn_dtree,dcodes-1);
}

/* ===========================================================================
 * Determine the best encoding for the current block: dynamic trees, static
 * trees or store, and output the encoded block to the zip file.
 */
local void flush_block(
    DeflateHandler encoder,
    int eof) /* true if this is the last block for a file */
{
    ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
    int max_blindex;	/* index of last bit length code of non zero freq */
    ulg stored_len;	/* length of input block */

    stored_len = (ulg)(encoder->strstart - encoder->block_start);
    encoder->flag_buf[encoder->last_flags] = encoder->flags; /* Save the flags for the last 8 items */

    /* Construct the literal and distance trees */
    build_tree(encoder, (tree_desc near *)(&encoder->l_desc));
    Tracev((stderr, "\nlit data: dyn %ld, stat %ld",
	    encoder->opt_len, encoder->static_len));

    build_tree(encoder, (tree_desc near *)(&encoder->d_desc));
    Tracev((stderr, "\ndist data: dyn %ld, stat %ld",
	    encoder->opt_len, encoder->static_len));
    /* At this point, opt_len and static_len are the total bit lengths of
     * the compressed block data, excluding the tree representations.
     */

    /* Build the bit length tree for the above two trees, and get the index
     * in bl_order of the last bit length code to send.
     */
    max_blindex = build_bl_tree(encoder);

    /* Determine the best encoding. Compute first the block length in bytes */
    opt_lenb	= (encoder->opt_len   +3+7)>>3;
    static_lenb = (encoder->static_len+3+7)>>3;

    Trace((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u dist %u ",
	   opt_lenb, encoder->opt_len,
	   static_lenb, encoder->static_len, stored_len,
	   encoder->last_lit, encoder->last_dist));

    if(static_lenb <= opt_lenb)
	opt_lenb = static_lenb;
    if(stored_len + 4 <= opt_lenb /* 4: two words for the lengths */
       && encoder->block_start >= 0L) {
	unsigned int i;
	uch *p;

	/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
	 * Otherwise we can't have processed more than WSIZE input bytes since
	 * the last block flush, because compression would have been
	 * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
	 * transform a block into a stored block.
	 */
	send_bits(encoder, (STORED_BLOCK<<1)+eof, 3);  /* send block type */
	bi_windup(encoder);		 /* align on byte boundary */
	put_short((ush)stored_len);
	put_short((ush)~stored_len);

	/* copy block */
	p = &encoder->window[(unsigned)encoder->block_start];
	for(i = 0; i < stored_len; i++)
	    put_byte(p[i]);
    } else if(static_lenb == opt_lenb) {
	send_bits(encoder, (STATIC_TREES<<1)+eof, 3);
	compress_block(encoder,
		       (ct_data near *)encoder->static_ltree,
		       (ct_data near *)encoder->static_dtree);
    } else {
	send_bits(encoder, (DYN_TREES<<1)+eof, 3);
	send_all_trees(encoder,
		       encoder->l_desc.max_code+1,
		       encoder->d_desc.max_code+1,
		       max_blindex+1);
	compress_block(encoder,
		       (ct_data near *)encoder->dyn_ltree,
		       (ct_data near *)encoder->dyn_dtree);
    }

    init_block(encoder);

    if(eof)
	bi_windup(encoder);
}

/* ===========================================================================
 * Save the match info and tally the frequency counts. Return true if
 * the current block must be flushed.
 */
local int ct_tally(
    DeflateHandler encoder,
    int dist,	/* distance of matched string */
    int lc)	/* match length-MIN_MATCH or unmatched char (if dist==0) */
{
    encoder->l_buf[encoder->last_lit++] = (uch)lc;
    if(dist == 0) {
	/* lc is the unmatched char */
	encoder->dyn_ltree[lc].Freq++;
    } else {
	/* Here, lc is the match length - MIN_MATCH */
	dist--;		    /* dist = match distance - 1 */
	Assert((ush)dist < (ush)MAX_DIST &&
	       (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&
	       (ush)D_CODE(dist) < (ush)D_CODES,  "ct_tally: bad match");

	encoder->dyn_ltree[encoder->length_code[lc]+LITERALS+1].Freq++;
	encoder->dyn_dtree[D_CODE(dist)].Freq++;

	encoder->d_buf[encoder->last_dist++] = (ush)dist;
	encoder->flags |= encoder->flag_bit;
    }
    encoder->flag_bit <<= 1;

    /* Output the flags if they fill a byte: */
    if((encoder->last_lit & 7) == 0) {
	encoder->flag_buf[encoder->last_flags++] = encoder->flags;
	encoder->flags = 0;
	encoder->flag_bit = 1;
    }
    /* Try to guess if it is profitable to stop the current block here */
    if(encoder->compr_level > 2 && (encoder->last_lit & 0xfff) == 0) {
	/* Compute an upper bound for the compressed length */
	ulg out_length = (ulg)encoder->last_lit*8L;
	ulg in_length = (ulg)encoder->strstart - encoder->block_start;
	int dcode;

	for(dcode = 0; dcode < D_CODES; dcode++) {
	    out_length +=
		(ulg)encoder->dyn_dtree[dcode].Freq *
		    (5L + extra_dbits[dcode]);
	}
	out_length >>= 3;
	Trace((stderr,"\nlast_lit %u, last_dist %u, in %ld, out ~%ld(%ld%%) ",
	       encoder->last_lit, encoder->last_dist, in_length, out_length,
	       100L - out_length*100L/in_length));
	if(encoder->last_dist < encoder->last_lit/2 &&
	    out_length < in_length/2)
	    return 1;
    }
    return (encoder->last_lit == LIT_BUFSIZE-1 ||
	    encoder->last_dist == DIST_BUFSIZE);
    /* We avoid equality with LIT_BUFSIZE because of wraparound at 64K
     * on 16 bit machines and because stored blocks are restricted to
     * 64K-1 bytes.
     */
}

/* ===========================================================================
 * Send the block data compressed using the given Huffman trees
 */
local void compress_block(
    DeflateHandler encoder,
    ct_data near *ltree, /* literal tree */
    ct_data near *dtree) /* distance tree */
{
    unsigned dist;	/* distance of matched string */
    int lc;		/* match length or unmatched char (if dist == 0) */
    unsigned lx = 0;	/* running index in l_buf */
    unsigned dx = 0;	/* running index in d_buf */
    unsigned fx = 0;	/* running index in flag_buf */
    uch flag = 0;	/* current flags */
    unsigned code;	/* the code to send */
    int extra;		/* number of extra bits to send */

    if(encoder->last_lit != 0) do {
	if((lx & 7) == 0)
	    flag = encoder->flag_buf[fx++];
	lc = encoder->l_buf[lx++];
	if((flag & 1) == 0) {
	    SEND_CODE(lc, ltree); /* send a literal byte */
	    Tracecv(isgraph(lc), (stderr," '%c' ", lc));
	} else {
	    /* Here, lc is the match length - MIN_MATCH */
	    code = encoder->length_code[lc];
	    SEND_CODE(code+LITERALS+1, ltree); /* send the length code */
	    extra = extra_lbits[code];
	    if(extra != 0) {
		lc -= encoder->base_length[code];
		send_bits(encoder, lc, extra); /* send the extra length bits */
	    }
	    dist = encoder->d_buf[dx++];
	    /* Here, dist is the match distance - 1 */
	    code = D_CODE(dist);
	    Assert (code < D_CODES, "bad d_code");

	    SEND_CODE(code, dtree);	  /* send the distance code */
	    extra = extra_dbits[code];
	    if(extra != 0) {
		dist -= encoder->base_dist[code];
		send_bits(encoder, dist, extra);   /* send the extra distance bits */
	    }
	} /* literal or match pair ? */
	flag >>= 1;
    } while(lx < encoder->last_lit);

    SEND_CODE(END_BLOCK, ltree);
}

/* ===========================================================================
 * Send a value on a given number of bits.
 * IN assertion: length <= 16 and value fits in length bits.
 */
#define Buf_size (8 * sizeof(ush)) /* bit size of bi_buf */
local void send_bits(
    DeflateHandler encoder,
    int value,	/* value to send */
    int le