pgpztrees.c

著名的加密软件的应用于电子邮件中

*/
static void
scan_tree(struct ct_data near *tree, int max_code)
{
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 = (word16)-1; /* 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) {
bl_tree[curlen].Freq += count;
} else if (curlen != 0) {
if (curlen != prevlen)
bl_tree[curlen].Freq++;
bl_tree[REP_3_6].Freq++;
} else if (count <= 10) {
bl_tree[REPZ_3_10].Freq++;
} else {
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.
*/
static void
send_tree(struct ct_data near *tree, int max_code)
{
		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, bl_tree);
		} while (--count != 0);
		} else if (curlen != 0) {
			if (curlen != prevlen) {
		send_code(curlen, bl_tree);
		count--;
		}
		ZipAssert(count >= 3 && count <= 6, " 3_6?");
		send_code(REP_3_6, bl_tree);
		send_bits(count-3, 2);
		} else if (count <= 10) {
		send_code(REPZ_3_10, bl_tree);
		send_bits(count-3, 3);
		} else {
		send_code(REPZ_11_138, bl_tree);
		send_bits(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.
*/
static int
build_bl_tree(void)
{
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(dyn_ltree, l_desc.max_code);
scan_tree(dyn_dtree, d_desc.max_code);

/* Build the bit length tree: */
build_tree(&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 (bl_tree[bl_order[max_blindex]].Len != 0)
break;
}
/* Update opt_len to include the bit length tree and counts */
opt_len += 3*(max_blindex+1) + 5+5+4;
Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld", opt_len, 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.
*/
static void
send_all_trees(int lcodes, int dcodes, int blcodes)
{
int rank; /* index in bl_order */

ZipAssert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4,
"not enough codes");
ZipAssert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
"too many codes");
Tracev((stderr, "\nbl counts: "));
send_bits(lcodes-257, 5);
/* not +255 as stated in appnote.txt 1.93a or -256 in 2.04c */
send_bits(dcodes-1, 5);
send_bits(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(bl_tree[bl_order[rank]].Len, 3);
}
Tracev((stderr, "\nbl tree: sent %ld", bits_sent));

/* send the literal tree */
send_tree((struct ct_data near *)dyn_ltree, lcodes-1);
Tracev((stderr, "\nlit tree: sent %ld", bits_sent));

/* send the distance tree */
send_tree((struct ct_data near *)dyn_dtree, dcodes-1);
Tracev((stderr, "\ndist tree: sent %ld", bits_sent));
}

/* ===========================================================================
* Determine the best encoding for the current block: dynamic trees, static
* trees or store, and output the encoded block to the zip file. This function
* returns the total compressed length for the file so far.
*
* buf: the input block, or NULL if too old
* stored_len: the length of the input block
* eof: true if this is the last block for the file
*/
word32
flush_block(char const *buf, word32 stored_len, int eof)
{
word32 opt_lenb, static_lenb; /* opt_len and static_len in bytes */
int max_blindex; /* index of last bit length code of non zero freq */

flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */

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

build_tree((struct tree_desc near *)(&d_desc));
Tracev((stderr, "\ndist data: dyn %ld, stat %ld", opt_len, 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();

/* Determine the best encoding. Compute first the block length in bytes */
opt_lenb = (opt_len+3+7)>>3;
static_lenb = (static_len+3+7)>>3;
input_len += stored_len; /* for debugging only */

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

if (static_lenb <= opt_lenb) opt_lenb = static_lenb;

#ifndef PGP /* PGP can't handle stored files - disable this test */
/*
* If compression failed and this is the first and last block,
* and if the zip file can be seeked (to rewrite the local header),
* the whole file is transformed into a stored file:
*/
#ifdef FORCE_METHOD
if (level == 1 && eof && compressed_len == 0L) { /* force stored file */
#else
if (stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
#endif
/* Since LIT_BUFSIZE <= 2*WSIZE, the input data must be there: */
if (buf == NULL) error ("block vanished");

copy_block(buf, (unsigned)stored_len, 0); /* without header */
compressed_len = stored_len << 3;
} else
#endif /* PGP */

#ifdef FORCE_METHOD
if (level == 2 && buf != (char*)NULL) { /* force stored block */
#else
if (stored_len+4 <= opt_lenb && buf != (char*)NULL) {
/* 4: two words for the lengths */
#endif
/* 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((STORED_BLOCK<<1)+eof, 3); /* send block type */
compressed_len = (compressed_len + 3 + 7) & ~7L;
	compressed_len += (stored_len + 4) << 3;

	copy_block(buf, (unsigned)stored_len, 1); /* with header */

#ifdef FORCE_METHOD
} else if (level == 3) { /* force static trees */
#else
} else if (static_lenb == opt_lenb) {
#endif
		send_bits((STATIC_TREES<<1)+eof, 3);
		compress_block((struct ct_data near *)static_ltree,
			(struct ct_data near *)static_dtree);
		compressed_len += 3 + static_len;
} else {
send_bits((DYN_TREES<<1)+eof, 3);
send_all_trees(l_desc.max_code+1, d_desc.max_code+1, max_blindex+1);
compress_block((struct ct_data near *)dyn_ltree,
	(struct ct_data near *)dyn_dtree);
compressed_len += 3 + opt_len;
}
ZipAssert (compressed_len == bits_sent, "bad compressed size");
init_block();

if (eof) {
#if defined(PGP) && !defined(MMAP)
/* Wipe out sensitive data for pgp */
# ifdef DYN_ALLOC
extern byte *window;
# else
extern byte window[];
# endif
memset(window, 0, (unsigned)(2*WSIZE-1)); /* -1 needed if WSIZE=32K */
#else /* !PGP */
ZipAssert (input_len == isize, "bad input size");
#endif
			bi_windup();
	compressed_len += 7; /* align on byte boundary */
}
Tracev((stderr,"\ncomprlen %lu(%lu) ", compressed_len>>3,
compressed_len-7*eof));

return compressed_len >> 3;
}

/* ===========================================================================
* Save the match info and tally the frequency counts. Return true if
* the current block must be flushed.
*
* dist is the distance to the matched string, or 0 if none.
* lc is the length of the match, or the character if dist == 0.
*/
int
ct_tally(unsigned dist, unsigned lc)
{
l_buf[last_lit++] = (byte)lc;
if (dist == 0) {
/* lc is the unmatched char */
dyn_ltree[lc].Freq++;
} else {
/* Here, lc is the match length - MIN_MATCH */
dist--; /* dist = match distance - 1 */
ZipAssert((word16)dist < (word16)MAX_DIST &&
(word16)lc <= (word16)(MAX_MATCH-MIN_MATCH) &&
(word16)d_code(dist) < (word16)D_CODES, "ct_tally: bad match");

dyn_ltree[length_code[lc]+LITERALS+1].Freq++;
dyn_dtree[d_code(dist)].Freq++;

d_buf[last_dist++] = (word16)dist;
flags |= flag_bit;
}
flag_bit <<= 1;

/* Output the flags if they fill a byte: */
if ((last_lit & 7) == 0) {
flag_buf[last_flags++] = flags;
flags = 0, flag_bit = 1;
}
/* Try to guess if it is profitable to stop the current block here */
if (/* level > 2 && */ (last_lit & 0xfff) == 0) {
/* Compute an upper bound for the compressed length */
word32 out_length = (word32)last_lit*8L;
word32 in_length = (word32)strstart-block_start;
int dcode;

for (dcode = 0; dcode < D_CODES; dcode++)
out_length += (word32)
	dyn_dtree[dcode].Freq*(5L+extra_dbits[dcode]);
out_length >>= 3;
Trace((stderr,"\nlast_lit %u, last_dist %u, in %ld, out ~%ld(%ld%%) ",
last_lit, last_dist, in_length, out_length,
100L - out_length*100L/in_length));
if (last_dist < last_lit/2 && out_length < in_length/2) return 1;
}
return (last_lit == LIT_BUFSIZE-1 || 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
*/
static void
compress_block(struct ct_data near *ltree, struct ct_data near *dtree)
{
	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 */
	byte flag = 0;	/* current flags */
	unsigned code;	/* the code to send */
	int extra;	/* number of extra bits to send */

		if (last_lit != 0) do {
		if ((lx & 7) == 0)
			flag = flag_buf[fx++];
		lc = 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 = length_code[lc];
		send_code(code+LITERALS+1, ltree); /* send the length code */
		extra = extra_lbits[code];
		if (extra != 0) {
		lc -= base_length[code];
	send_bits(lc, extra);	/* send the extra length bits */
	}
	dist = d_buf[dx++];
/* Here, dist is the match distance - 1 */
code = d_code(dist);
ZipAssert (code < D_CODES, "bad d_code");

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

		send_code(END_BLOCK, ltree);
	}