# Category : C Source Code

Archive : PGP20SRC.ZIP

Filename : ZTREES.C

Copyright (C) 1990-1992 Mark Adler, Richard B. Wales, Jean-loup Gailly,

Kai Uwe Rommel and Igor Mandrichenko.

Permission is granted to any individual or institution to use, copy, or

redistribute this software so long as all of the original files are included

unmodified, that it is not sold for profit, and that this copyright notice

is retained.

*/

/*

* trees.c by Jean-loup Gailly

*

* This is a new version of im_ctree.c originally written by Richard B. Wales

* for the defunct implosion method.

*

* PURPOSE

*

* Encode various sets of source values using variable-length

* binary code trees.

*

* DISCUSSION

*

* The PKZIP "deflation" process uses several Huffman trees. The more

* common source values are represented by shorter bit sequences.

*

* Each code tree is stored in the ZIP file in a compressed form

* which is itself a Huffman encoding of the lengths of

* all the code strings (in ascending order by source values).

* The actual code strings are reconstructed from the lengths in

* the UNZIP process, as described in the "application note"

* (APPNOTE.TXT) distributed as part of PKWARE's PKZIP program.

*

* REFERENCES

*

* Lynch, Thomas J.

* Data Compression: Techniques and Applications, pp. 53-55.

* Lifetime Learning Publications, 1985. ISBN 0-534-03418-7.

*

* Storer, James A.

* Data Compression: Methods and Theory, pp. 49-50.

* Computer Science Press, 1988. ISBN 0-7167-8156-5.

*

* Sedgewick, R.

* Algorithms, p290.

* Addison-Wesley, 1983. ISBN 0-201-06672-6.

*

* INTERFACE

*

* void ct_init (ush *attr, int *method)

* Allocate the match buffer, initialize the various tables and save

* the location of the internal file attribute (ascii/binary) and

* method (DEFLATE/STORE)

*

* void ct_tally (int dist, int lc);

* Save the match info and tally the frequency counts.

*

* long flush_block (char *buf, ulg stored_len, int eof)

* Determine the best encoding for the current block: dynamic trees,

* static trees or store, and output the encoded block to the zip

* file. Returns the total compressed length for the file so far.

*

*/

#include

#include "zip.h"

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

* Constants

*/

#define MAX_BITS 15

/* All codes must not exceed MAX_BITS bits */

#define MAX_BL_BITS 7

/* Bit length codes must not exceed MAX_BL_BITS bits */

#define LENGTH_CODES 29

/* number of length codes, not counting the special END_BLOCK code */

#define LITERALS 256

/* number of literal bytes 0..255 */

#define END_BLOCK 256

/* end of block literal code */

#define L_CODES (LITERALS+1+LENGTH_CODES)

/* number of Literal or Length codes, including the END_BLOCK code */

#define D_CODES 30

/* number of distance codes */

#define BL_CODES 19

/* number of codes used to transfer the bit lengths */

local int near extra_lbits[LENGTH_CODES] /* extra bits for each length code */

= {0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0};

local int near extra_dbits[D_CODES] /* extra bits for each distance code */

= {0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

local int near extra_blbits[BL_CODES]/* extra bits for each bit length code */

= {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};

#define STORED_BLOCK 0

#define STATIC_TREES 1

#define DYN_TREES 2

/* The three kinds of block type */

#ifndef LIT_BUFSIZE

# ifdef SMALL_MEM

# define LIT_BUFSIZE 0x2000

# else

# ifdef MEDIUM_MEM

# define LIT_BUFSIZE 0x4000

# else

# define LIT_BUFSIZE 0x8000

# endif

# endif

#endif

#define DIST_BUFSIZE LIT_BUFSIZE

/* Sizes of match buffers for literals/lengths and distances. There are

* 4 reasons for limiting LIT_BUFSIZE to 64K:

* - frequencies can be kept in 16 bit counters

* - if compression is not successful for the first block, all input data is

* still in the window so we can still emit a stored block even when input

* comes from standard input. (This can also be done for all blocks if

* LIT_BUFSIZE is not greater than 32K.)

* - if compression is not successful for a file smaller than 64K, we can

* even emit a stored file instead of a stored block (saving 5 bytes).

* - creating new Huffman trees less frequently may not provide fast

* adaptation to changes in the input data statistics. (Take for

* example a binary file with poorly compressible code followed by

* a highly compressible string table.) Smaller buffer sizes give

* fast adaptation but have of course the overhead of transmitting trees

* more frequently.

* - I can't count above 4

* The current code is general and allows DIST_BUFSIZE < LIT_BUFSIZE (to save

* memory at the expense of compression). Some optimizations would be possible

* if we rely on DIST_BUFSIZE == LIT_BUFSIZE.

*/

#define REP_3_6 16

/* repeat previous bit length 3-6 times (2 bits of repeat count) */

#define REPZ_3_10 17

/* repeat a zero length 3-10 times (3 bits of repeat count) */

#define REPZ_11_138 18

/* repeat a zero length 11-138 times (7 bits of repeat count) */

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

* Local data

*/

/* Data structure describing a single value and its code string. */

typedef struct ct_data {

union {

ush freq; /* frequency count */

ush code; /* bit string */

} fc;

union {

ush dad; /* father node in Huffman tree */

ush len; /* length of bit string */

} dl;

} ct_data;

#define Freq fc.freq

#define Code fc.code

#define Dad dl.dad

#define Len dl.len

#define HEAP_SIZE (2*L_CODES+1)

/* maximum heap size */

local ct_data near dyn_ltree[HEAP_SIZE]; /* literal and length tree */

local ct_data near dyn_dtree[2*D_CODES+1]; /* distance tree */

local ct_data near static_ltree[L_CODES+2];

/* The static literal tree. Since the bit lengths are imposed, there is no

* need for the L_CODES extra codes used during heap construction. However

* The codes 286 and 287 are needed to build a canonical tree (see ct_init

* below).

*/

local ct_data near static_dtree[D_CODES];

/* The static distance tree. (Actually a trivial tree since all codes use

* 5 bits.)

*/

local ct_data near bl_tree[2*BL_CODES+1];

/* Huffman tree for the bit lengths */

typedef struct tree_desc {

ct_data near *dyn_tree; /* the dynamic tree */

ct_data near *static_tree; /* corresponding static tree or NULL */

int near *extra_bits; /* extra bits for each code or NULL */

int extra_base; /* base index for extra_bits */

int elems; /* max number of elements in the tree */

int max_length; /* max bit length for the codes */

int max_code; /* largest code with non zero frequency */

} tree_desc;

local tree_desc near l_desc =

{dyn_ltree, static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS, 0};

local tree_desc near d_desc =

{dyn_dtree, static_dtree, extra_dbits, 0, D_CODES, MAX_BITS, 0};

local tree_desc near bl_desc =

{bl_tree, NULL, extra_blbits, 0, BL_CODES, MAX_BL_BITS, 0};

local ush near bl_count[MAX_BITS+1];

/* number of codes at each bit length for an optimal tree */

local uch near bl_order[BL_CODES]

= {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};

/* The lengths of the bit length codes are sent in order of decreasing

* probability, to avoid transmitting the lengths for unused bit length codes.

*/

local int near heap[2*L_CODES+1]; /* heap used to build the Huffman trees */

local int heap_len; /* number of elements in the heap */

local int heap_max; /* element of largest frequency */

/* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.

* The same heap array is used to build all trees.

*/

local uch near depth[2*L_CODES+1];

/* Depth of each subtree used as tie breaker for trees of equal frequency */

local uch length_code[MAX_MATCH-MIN_MATCH+1];

/* length code for each normalized match length (0 == MIN_MATCH) */

local uch dist_code[512];

/* distance codes. The first 256 values correspond to the distances

* 3 .. 258, the last 256 values correspond to the top 8 bits of

* the 15 bit distances.

*/

local int near base_length[LENGTH_CODES];

/* First normalized length for each code (0 = MIN_MATCH) */

local int near base_dist[D_CODES];

/* First normalized distance for each code (0 = distance of 1) */

#ifndef DYN_ALLOC

local uch far l_buf[LIT_BUFSIZE]; /* buffer for literals/lengths */

local ush far d_buf[DIST_BUFSIZE]; /* buffer for distances */

#else

local uch far *l_buf;

local ush far *d_buf;

#endif

local uch near flag_buf[(LIT_BUFSIZE/8)];

/* flag_buf is a bit array distinguishing literals from lengths in

* l_buf, and thus indicating the presence or absence of a distance.

*/

local unsigned last_lit; /* running index in l_buf */

local unsigned last_dist; /* running index in d_buf */

local unsigned last_flags; /* running index in flag_buf */

local uch flags; /* current flags not yet saved in flag_buf */

local uch flag_bit; /* current bit used in flags */

/* bits are filled in flags starting at bit 0 (least significant).

* Note: these flags are overkill in the current code since we don't

* take advantage of DIST_BUFSIZE == LIT_BUFSIZE.

*/

local ulg opt_len; /* bit length of current block with optimal trees */

local ulg static_len; /* bit length of current block with static trees */

local ulg compressed_len; /* total bit length of compressed file */

local ulg input_len; /* total byte length of input file */

/* input_len is for debugging only since we can get it by other means. */

ush *file_type; /* pointer to UNKNOWN, BINARY or ASCII */

int *file_method; /* pointer to DEFLATE or STORE */

#ifdef DEBUG

extern ulg bits_sent; /* bit length of the compressed data */

extern ulg isize; /* byte length of input file */

#endif

extern long block_start; /* window offset of current block */

extern unsigned near strstart; /* window offset of current string */

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

* Local (static) routines in this file.

*/

local void init_block OF((void));

local void pqdownheap OF((ct_data near *tree, int k));

local void gen_bitlen OF((tree_desc near *desc));

local void gen_codes OF((ct_data near *tree, int max_code));

local void build_tree OF((tree_desc near *desc));

local void scan_tree OF((ct_data near *tree, int max_code));

local void send_tree OF((ct_data near *tree, int max_code));

local int build_bl_tree OF((void));

local void send_all_trees OF((int lcodes, int dcodes, int blcodes));

local void compress_block OF((ct_data near *ltree, ct_data near *dtree));

local void set_file_type OF((void));

#ifndef DEBUG

# define send_code(c, tree) send_bits(tree[c].Code, tree[c].Len)

/* Send a code of the given tree. c and tree must not have side effects */

#else /* DEBUG */

# define send_code(c, tree) \

{ if (verbose>1) fprintf(stderr,"\ncd %3d ",(c)); \

send_bits(tree[c].Code, tree[c].Len); }

#endif

#define d_code(dist) \

((dist) < 256 ? dist_code[dist] : dist_code[256+((dist)>>7)])

/* Mapping from a distance to a distance code. dist is the distance - 1 and

* must not have side effects. dist_code[256] and dist_code[257] are never

* used.

*/

#define MAX(a,b) (a >= b ? a : b)

/* the arguments must not have side effects */

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

* Allocate the match buffer, initialize the various tables and save the

* location of the internal file attribute (ascii/binary) and method

* (DEFLATE/STORE).

*/

void ct_init(attr, method)

ush *attr; /* pointer to internal file attribute */

int *method; /* pointer to compression method */

{

int n; /* iterates over tree elements */

int bits; /* bit counter */

int length; /* length value */

int code; /* code value */

int dist; /* distance index */

file_type = attr;

file_method = method;

compressed_len = input_len = 0L;

if (static_dtree[0].Len != 0) return; /* ct_init already called */

#ifdef DYN_ALLOC

d_buf = (ush far*) fcalloc(DIST_BUFSIZE, sizeof(ush));

l_buf = (uch far*) fcalloc(LIT_BUFSIZE/2, 2);

/* Avoid using the value 64K on 16 bit machines */

if (l_buf == NULL || d_buf == NULL) error("ct_init: out of memory");

#endif

/* Initialize the mapping length (0..255) -> length code (0..28) */

length = 0;

for (code = 0; code < LENGTH_CODES-1; code++) {

base_length[code] = length;

for (n = 0; n < (1<

}

}

Assert (length == 256, "ct_init: length != 256");

/* Note that the length 255 (match length 258) can be represented

* in two different ways: code 284 + 5 bits or code 285, so we

* overwrite length_code[255] to use the best encoding:

*/

length_code[length-1] = (uch)code;

/* Initialize the mapping dist (0..32K) -> dist code (0..29) */

dist = 0;

for (code = 0 ; code < 16; code++) {

base_dist[code] = dist;

for (n = 0; n < (1<

}

}

Assert (dist == 256, "ct_init: dist != 256");

dist >>= 7; /* from now on, all distances are divided by 128 */

for ( ; code < D_CODES; code++) {

base_dist[code] = dist << 7;

for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {

dist_code[256 + dist++] = (uch)code;

}

}

Assert (dist == 256, "ct_init: 256+dist != 512");

/* Construct the codes of the static literal tree */

for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;

n = 0;

while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;

while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;

while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;

while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;

/* Codes 286 and 287 do not exist, but we must include them in the

* tree construction to get a canonical Huffman tree (longest code

* all ones)

*/

gen_codes(static_ltree, L_CODES+1);

/* The static distance tree is trivial: */

for (n = 0; n < D_CODES; n++) {

static_dtree[n].Len = 5;

static_dtree[n].Code = bi_reverse(n, 5);

}

/* Initialize the first block of the first file: */

init_block();

}

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

* Initialize a new block.

*/

local void init_block()

{

int n; /* iterates over tree elements */

/* Initialize the trees. */

for (n = 0; n < L_CODES; n++) dyn_ltree[n].Freq = 0;

for (n = 0; n < D_CODES; n++) dyn_dtree[n].Freq = 0;

for (n = 0; n < BL_CODES; n++) bl_tree[n].Freq = 0;

dyn_ltree[END_BLOCK].Freq = 1;

opt_len = static_len = 0L;

last_lit = last_dist = last_flags = 0;

flags = 0; flag_bit = 1;

}

#define SMALLEST 1

/* Index within the heap array of least frequent node in the Huffman tree */

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

* Remove the smallest element from the heap and recreate the heap with

* one less element. Updates heap and heap_len.

*/

#define pqremove(tree, top) \

{\

top = heap[SMALLEST]; \

heap[SMALLEST] = heap[heap_len--]; \

pqdownheap(tree, SMALLEST); \

}

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

* Compares to subtrees, using the tree depth as tie breaker when

* the subtrees have equal frequency. This minimizes the worst case length.

*/

#define smaller(tree, n, m) \

(tree[n].Freq < tree[m].Freq || \

(tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))

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

* Restore the heap property by moving down the tree starting at node k,

* exchanging a node with the smallest of its two sons if necessary, stopping

* when the heap property is re-established (each father smaller than its

* two sons).

*/

local void pqdownheap(tree, k)

ct_data near *tree; /* the tree to restore */

int k; /* node to move down */

{

int v = heap[k];

int j = k << 1; /* left son of k */

while (j <= heap_len) {

/* Set j to the smallest of the two sons: */

if (j < heap_len && smaller(tree, heap[j+1], heap[j])) j++;

/* Exit if v is smaller than both sons */

if (smaller(tree, v, heap[j])) break;

/* Exchange v with the smallest son */

heap[k] = heap[j], k = j;

/* And continue down the tree, setting j to the left son of k */

j <<= 1;

}

heap[k] = v;

}

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

* Compute the optimal bit lengths for a tree and update the total bit length

* for the current block.

* IN assertion: the fields freq and dad are set, heap[heap_max] and

* above are the tree nodes sorted by increasing frequency.

* OUT assertions: the field len is set to the optimal bit length, the

* array bl_count contains the frequencies for each bit length.

* The length opt_len is updated; static_len is also updated if stree is

* not null.

*/

local void gen_bitlen(desc)

tree_desc near *desc; /* the tree descriptor */

{

ct_data near *tree = desc->dyn_tree;

int near *extra = desc->extra_bits;

int base = desc->extra_base;

int max_code = desc->max_code;

int max_length = desc->max_length;

ct_data near *stree = desc->static_tree;

int h; /* heap index */

int n, m; /* iterate over the tree elements */

int bits; /* bit length */

int xbits; /* extra bits */

ush f; /* frequency */

int overflow = 0; /* number of elements with bit length too large */

for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;

/* In a first pass, compute the optimal bit lengths (which may

* overflow in the case of the bit length tree).

*/

tree[heap[heap_max]].Len = 0; /* root of the heap */

for (h = heap_max+1; h < HEAP_SIZE; h++) {

n = heap[h];

bits = tree[tree[n].Dad].Len + 1;

if (bits > max_length) bits = max_length, overflow++;

tree[n].Len = bits;

/* We overwrite tree[n].Dad which is no longer needed */

if (n > max_code) continue; /* not a leaf node */

bl_count[bits]++;

xbits = 0;

if (n >= base) xbits = extra[n-base];

f = tree[n].Freq;

opt_len += (ulg)f * (bits + xbits);

if (stree) static_len += (ulg)f * (stree[n].Len + xbits);

}

if (overflow == 0) return;

Trace((stderr,"\nbit length overflow\n"));

/* This happens for example on obj2 and pic of the Calgary corpus */

/* Find the first bit length which could increase: */

do {

bits = max_length-1;

while (bl_count[bits] == 0) bits--;

bl_count[bits]--; /* move one leaf down the tree */

bl_count[bits+1] += 2; /* move one overflow item as its brother */

bl_count[max_length]--;

/* The brother of the overflow item also moves one step up,

* but this does not affect bl_count[max_length]

*/

overflow -= 2;

} while (overflow > 0);

/* Now recompute all bit lengths, scanning in increasing frequency.

* h is still equal to HEAP_SIZE. (It is simpler to reconstruct all

* lengths instead of fixing only the wrong ones. This idea is taken

* from 'ar' written by Haruhiko Okumura.)

*/

for (bits = max_length; bits != 0; bits--) {

n = bl_count[bits];

while (n != 0) {

m = heap[--h];

if (m > max_code) continue;

if (tree[m].Len != (unsigned) bits) {

Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));

opt_len += ((long)bits-(long)tree[m].Len)*(long)tree[m].Freq;

tree[m].Len = bits;

}

n--;

}

}

}

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

* Generate the codes for a given tree and bit counts (which need not be

* optimal).

* IN assertion: the array bl_count contains the bit length statistics for

* the given tree and the field len is set for all tree elements.

* OUT assertion: the field code is set for all tree elements of non

* zero code length.

*/

local void gen_codes (tree, max_code)

ct_data near *tree; /* the tree to decorate */

int max_code; /* largest code with non zero frequency */

{

ush next_code[MAX_BITS+1]; /* next code value for each bit length */

ush code = 0; /* running code value */

int bits; /* bit index */

int n; /* code index */

/* The distribution counts are first used to generate the code values

* without bit reversal.

*/

for (bits = 1; bits <= MAX_BITS; bits++) {

next_code[bits] = code = (code + bl_count[bits-1]) << 1;

}

/* Check that the bit counts in bl_count are consistent. The last code

* must be all ones.

*/

Assert (code + bl_count[MAX_BITS]-1 == (1<

Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

for (n = 0; n <= max_code; n++) {

int len = tree[n].Len;

if (len == 0) continue;

/* Now reverse the bits */

tree[n].Code = bi_reverse(next_code[len]++, len);

Tracec(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",

n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));

}

}

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

* Construct one Huffman tree and assigns the code bit strings and lengths.

* Update the total bit length for the current block.

* IN assertion: the field freq is set for all tree elements.

* OUT assertions: the fields len and code are set to the optimal bit length

* and corresponding code. The length opt_len is updated; static_len is

* also updated if stree is not null. The field max_code is set.

*/

local void build_tree(desc)

tree_desc near *desc; /* the tree descriptor */

{

ct_data near *tree = desc->dyn_tree;

ct_data near *stree = desc->static_tree;

int elems = desc->elems;

int n, m; /* iterate over heap elements */

int max_code = -1; /* largest code with non zero frequency */

int node = elems; /* next internal node of the tree */

/* Construct the initial heap, with least frequent element in

* heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].

* heap[0] is not used.

*/

heap_len = 0, heap_max = HEAP_SIZE;

for (n = 0; n < elems; n++) {

if (tree[n].Freq != 0) {

heap[++heap_len] = max_code = n;

depth[n] = 0;

} else {

tree[n].Len = 0;

}

}

/* The pkzip format requires that at least one distance code exists,

* and that at least one bit should be sent even if there is only one

* possible code. So to avoid special checks later on we force at least

* two codes of non zero frequency.

*/

while (heap_len < 2) {

int new = heap[++heap_len] = (max_code < 2 ? ++max_code : 0);

tree[new].Freq = 1;

depth[new] = 0;

opt_len--; if (stree) static_len -= stree[new].Len;

/* new is 0 or 1 so it does not have extra bits */

}

desc->max_code = max_code;

/* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,

* establish sub-heaps of increasing lengths:

*/

for (n = heap_len/2; n >= 1; n--) pqdownheap(tree, n);

/* Construct the Huffman tree by repeatedly combining the least two

* frequent nodes.

*/

do {

pqremove(tree, n); /* n = node of least frequency */

m = heap[SMALLEST]; /* m = node of next least frequency */

heap[--heap_max] = n; /* keep the nodes sorted by frequency */

heap[--heap_max] = m;

/* Create a new node father of n and m */

tree[node].Freq = tree[n].Freq + tree[m].Freq;

depth[node] = (uch) (MAX(depth[n], depth[m]) + 1);

tree[n].Dad = tree[m].Dad = node;

#ifdef DUMP_BL_TREE

if (tree == bl_tree) {

fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",

node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);

}

#endif

/* and insert the new node in the heap */

heap[SMALLEST] = node++;

pqdownheap(tree, SMALLEST);

} while (heap_len >= 2);

heap[--heap_max] = heap[SMALLEST];

/* At this point, the fields freq and dad are set. We can now

* generate the bit lengths.

*/

gen_bitlen(desc);

/* The field len is now set, we can generate the bit codes */

gen_codes (tree, max_code);

}

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

* 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 (tree, max_code)

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)-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.

*/

local void send_tree (tree, max_code)

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, bl_tree); } while (--count != 0);

} else if (curlen != 0) {

if (curlen != prevlen) {

send_code(curlen, bl_tree); count--;

}

Assert(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.

*/

local int build_bl_tree()

{

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.

*/

local void send_all_trees(lcodes, dcodes, blcodes)

int lcodes, dcodes, 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(lcodes-257, 5); /* not -255 as stated in appnote.txt */

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_tree(dyn_ltree, lcodes-1); /* send the literal tree */

Tracev((stderr, "\nlit tree: sent %ld", bits_sent));

send_tree(dyn_dtree, dcodes-1); /* send the distance tree */

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.

*/

ulg flush_block(buf, stored_len, eof)

char *buf; /* input block, or NULL if too old */

ulg stored_len; /* length of input block */

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 */

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

/* Check if the file is ascii or binary */

if (*file_type == (ush)UNKNOWN) set_file_type();

/* Construct the literal and distance trees */

build_tree(&l_desc);

Tracev((stderr, "\nlit data: dyn %ld, stat %ld", opt_len, static_len));

build_tree(&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;

#ifdef ZIP /* not ok for PGP */

/* 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;

*file_method = STORE;

} else

#endif /* ZIP */

#ifdef FORCE_METHOD

if (level == 2 && buf != NULL) { /* force stored block */

#else

if (stored_len+4 <= opt_lenb && buf != 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(static_ltree, 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(dyn_ltree, dyn_dtree);

compressed_len += 3 + opt_len;

}

Assert (compressed_len == bits_sent, "bad compressed size");

init_block();

if (eof) {

Assert (input_len == isize, "bad input size");

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.

*/

int ct_tally (dist, lc)

int dist; /* distance of matched string */

int lc; /* match length-MIN_MATCH or unmatched char (if dist==0) */

{

l_buf[last_lit++] = (uch)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 */

Assert((ush)dist < (ush)MAX_DIST &&

(ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&

(ush)d_code(dist) < (ush)D_CODES, "ct_tally: bad match");

dyn_ltree[length_code[lc]+LITERALS+1].Freq++;

dyn_dtree[d_code(dist)].Freq++;

d_buf[last_dist++] = 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 */

ulg out_length = (ulg)last_lit*8L;

ulg in_length = (ulg)strstart-block_start;

int dcode;

for (dcode = 0; dcode < D_CODES; dcode++) {

out_length += (ulg)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

*/

local void compress_block(ltree, dtree)

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 (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);

Assert (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);

}

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

* Set the file type to ASCII or BINARY, using a crude approximation:

* binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.

* IN assertion: the fields freq of dyn_ltree are set and the total of all

* frequencies does not exceed 64K (to fit in an int on 16 bit machines).

*/

local void set_file_type()

{

int n = 0;

unsigned ascii_freq = 0;

unsigned bin_freq = 0;

while (n < 7) bin_freq += dyn_ltree[n++].Freq;

while (n < 128) ascii_freq += dyn_ltree[n++].Freq;

while (n < LITERALS) bin_freq += dyn_ltree[n++].Freq;

*file_type = bin_freq > (ascii_freq >> 2) ? BINARY : ASCII;

#ifdef ZIP

if (*file_type == BINARY && translate_eol) {

warn("-l used on binary file", "");

}

#endif

}

Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/