cpython/Modules/zlib/trees.c at 3.5 · python/cpython · GitHub

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/* trees.c -- output deflated data using Huffman coding

* detect_data_type() function provided freely by Cosmin Truta, 2006

* For conditions of distribution and use, see copyright notice in zlib.h

* ALGORITHM

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

* common source values are represented by shorter bit sequences.

* Each code tree is stored 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 inflate process, as described

* in the deflate specification.

* REFERENCES

* Deutsch, L.P.,"'Deflate' Compressed Data Format Specification".

* Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc

* 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.

/* @(#) $Id$ */

/* #define GEN_TREES_H */

#include "deflate.h"

#ifdef ZLIB_DEBUG

# include <ctype.h>

#endif

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

* Constants

#define MAX_BL_BITS 7

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

#define END_BLOCK 256

/* end of block literal code */

#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 const int 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 const int 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 const int 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};

local const uch 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 data. These are initialized only once.

#define DIST_CODE_LEN 512 /* see definition of array dist_code below */

#if defined(GEN_TREES_H) || !defined(STDC)

/* non ANSI compilers may not accept trees.h */

local ct_data 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 _tr_init

* below).

local ct_data static_dtree[D_CODES];

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

* 5 bits.)

uch _dist_code[DIST_CODE_LEN];

/* 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.

uch _length_code[MAX_MATCH-MIN_MATCH+1];

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

local int base_length[LENGTH_CODES];

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

local int base_dist[D_CODES];

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

#else

# include "trees.h"

#endif /* GEN_TREES_H */

struct static_tree_desc_s {

const ct_data *static_tree; /* static tree or NULL */

const intf *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 */

};

local const static_tree_desc static_l_desc =

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

local const static_tree_desc static_d_desc =

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

local const static_tree_desc static_bl_desc =

{(const ct_data *)0, extra_blbits, 0, BL_CODES, MAX_BL_BITS};

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

* Local (static) routines in this file.

local void tr_static_init OF((void));

local void init_block OF((deflate_state *s));

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

local void gen_bitlen OF((deflate_state *s, tree_desc *desc));

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

local void build_tree OF((deflate_state *s, tree_desc *desc));

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

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

local int build_bl_tree OF((deflate_state *s));

local void send_all_trees OF((deflate_state *s, int lcodes, int dcodes,

int blcodes));

local void compress_block OF((deflate_state *s, const ct_data *ltree,

const ct_data *dtree));

local int detect_data_type OF((deflate_state *s));

local unsigned bi_reverse OF((unsigned value, int length));

local void bi_windup OF((deflate_state *s));

local void bi_flush OF((deflate_state *s));

#ifdef GEN_TREES_H

local void gen_trees_header OF((void));

#endif

#ifndef ZLIB_DEBUG

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

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

#else /* !ZLIB_DEBUG */

# define send_code(s, c, tree) \

{ if (z_verbose>2) fprintf(stderr,"\ncd %3d ",(c)); \

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

#endif

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

* Output a short LSB first on the stream.

* IN assertion: there is enough room in pendingBuf.

#define put_short(s, w) { \

put_byte(s, (uch)((w) & 0xff)); \

put_byte(s, (uch)((ush)(w) >> 8)); \

}

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

* Send a value on a given number of bits.

* IN assertion: length <= 16 and value fits in length bits.

#ifdef ZLIB_DEBUG

local void send_bits OF((deflate_state *s, int value, int length));

local void send_bits(s, value, length)

deflate_state *s;

int value; /* value to send */

int length; /* number of bits */

{

Tracevv((stderr," l %2d v %4x ", length, value));

Assert(length > 0 && length <= 15, "invalid length");

s->bits_sent += (ulg)length;

/* If not enough room in bi_buf, use (valid) bits from bi_buf and

* (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))

* unused bits in value.

if (s->bi_valid > (int)Buf_size - length) {

s->bi_buf |= (ush)value << s->bi_valid;

put_short(s, s->bi_buf);

s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);

s->bi_valid += length - Buf_size;

} else {

s->bi_buf |= (ush)value << s->bi_valid;

s->bi_valid += length;

}

#else /* !ZLIB_DEBUG */

#define send_bits(s, value, length) \

{ int len = length;\

if (s->bi_valid > (int)Buf_size - len) {\

int val = (int)value;\

s->bi_buf |= (ush)val << s->bi_valid;\

put_short(s, s->bi_buf);\

s->bi_buf = (ush)val >> (Buf_size - s->bi_valid);\

s->bi_valid += len - Buf_size;\

} else {\

s->bi_buf |= (ush)(value) << s->bi_valid;\

s->bi_valid += len;\

}

#endif /* ZLIB_DEBUG */

/* the arguments must not have side effects */

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

* Initialize the various 'constant' tables.

local void tr_static_init()

{

#if defined(GEN_TREES_H) || !defined(STDC)

static int static_init_done = 0;

int n; /* iterates over tree elements */

int bits; /* bit counter */

int length; /* length value */

int code; /* code value */

int dist; /* distance index */

ush bl_count[MAX_BITS+1];

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

if (static_init_done) return;

/* For some embedded targets, global variables are not initialized: */

#ifdef NO_INIT_GLOBAL_POINTERS

static_l_desc.static_tree = static_ltree;

static_l_desc.extra_bits = extra_lbits;

static_d_desc.static_tree = static_dtree;

static_d_desc.extra_bits = extra_dbits;

static_bl_desc.extra_bits = extra_blbits;

#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<<extra_lbits[code]); n++) {

_length_code[length++] = (uch)code;

}

Assert (length == 256, "tr_static_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<<extra_dbits[code]); n++) {

_dist_code[dist++] = (uch)code;

}

Assert (dist == 256, "tr_static_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, "tr_static_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((ct_data *)static_ltree, L_CODES+1, bl_count);

/* The static distance tree is trivial: */

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

static_dtree[n].Len = 5;

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

}

static_init_done = 1;

# ifdef GEN_TREES_H

gen_trees_header();

# endif

#endif /* defined(GEN_TREES_H) || !defined(STDC) */

}

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

* Genererate the file trees.h describing the static trees.

#ifdef GEN_TREES_H

# ifndef ZLIB_DEBUG

# include <stdio.h>

# endif

# define SEPARATOR(i, last, width) \

((i) == (last)? "\n};\n\n" : \

((i) % (width) == (width)-1 ? ",\n" : ", "))

void gen_trees_header()

{

FILE *header = fopen("trees.h", "w");

int i;

Assert (header != NULL, "Can't open trees.h");

fprintf(header,

"/* header created automatically with -DGEN_TREES_H */\n\n");

fprintf(header, "local const ct_data static_ltree[L_CODES+2] = {\n");

for (i = 0; i < L_CODES+2; i++) {

fprintf(header, "{{%3u},{%3u}}%s", static_ltree[i].Code,

static_ltree[i].Len, SEPARATOR(i, L_CODES+1, 5));

}

fprintf(header, "local const ct_data static_dtree[D_CODES] = {\n");

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

fprintf(header, "{{%2u},{%2u}}%s", static_dtree[i].Code,

static_dtree[i].Len, SEPARATOR(i, D_CODES-1, 5));

}

fprintf(header, "const uch ZLIB_INTERNAL _dist_code[DIST_CODE_LEN] = {\n");

for (i = 0; i < DIST_CODE_LEN; i++) {

fprintf(header, "%2u%s", _dist_code[i],

SEPARATOR(i, DIST_CODE_LEN-1, 20));

}

fprintf(header,

"const uch ZLIB_INTERNAL _length_code[MAX_MATCH-MIN_MATCH+1]= {\n");

for (i = 0; i < MAX_MATCH-MIN_MATCH+1; i++) {

fprintf(header, "%2u%s", _length_code[i],

SEPARATOR(i, MAX_MATCH-MIN_MATCH, 20));

}

fprintf(header, "local const int base_length[LENGTH_CODES] = {\n");

for (i = 0; i < LENGTH_CODES; i++) {

fprintf(header, "%1u%s", base_length[i],

SEPARATOR(i, LENGTH_CODES-1, 20));

}

fprintf(header, "local const int base_dist[D_CODES] = {\n");

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

fprintf(header, "%5u%s", base_dist[i],

SEPARATOR(i, D_CODES-1, 10));

}

fclose(header);

}

#endif /* GEN_TREES_H */

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

* Initialize the tree data structures for a new zlib stream.

void ZLIB_INTERNAL _tr_init(s)

deflate_state *s;

{

tr_static_init();

s->l_desc.dyn_tree = s->dyn_ltree;

s->l_desc.stat_desc = &static_l_desc;

s->d_desc.dyn_tree = s->dyn_dtree;

s->d_desc.stat_desc = &static_d_desc;

s->bl_desc.dyn_tree = s->bl_tree;

s->bl_desc.stat_desc = &static_bl_desc;

s->bi_buf = 0;

s->bi_valid = 0;

#ifdef ZLIB_DEBUG

s->compressed_len = 0L;

s->bits_sent = 0L;

#endif

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

init_block(s);

}

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

* Initialize a new block.

local void init_block(s)

deflate_state *s;

{

int n; /* iterates over tree elements */

/* Initialize the trees. */

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

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

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

s->dyn_ltree[END_BLOCK].Freq = 1;

s->opt_len = s->static_len = 0L;

s->last_lit = s->matches = 0;

}

#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(s, tree, top) \

top = s->heap[SMALLEST]; \

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

pqdownheap(s, 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, depth) \

(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(s, tree, k)

deflate_state *s;

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

int k; /* node to move down */

{

int v = s->heap[k];

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

while (j <= s->heap_len) {

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

if (j < s->heap_len &&

smaller(tree, s->heap[j+1], s->heap[j], s->depth)) {

j++;

}

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

if (smaller(tree, v, s->heap[j], s->depth)) break;

/* Exchange v with the smallest son */

s->heap[k] = s->heap[j]; k = j;

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

j <<= 1;

}

s->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(s, desc)

deflate_state *s;

tree_desc *desc; /* the tree descriptor */

{

ct_data *tree = desc->dyn_tree;

int max_code = desc->max_code;

const ct_data *stree = desc->stat_desc->static_tree;

const intf *extra = desc->stat_desc->extra_bits;

int base = desc->stat_desc->extra_base;

int max_length = desc->stat_desc->max_length;

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++) s->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[s->heap[s->heap_max]].Len = 0; /* root of the heap */

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

n = s->heap[h];

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

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

tree[n].Len = (ush)bits;

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

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

s->bl_count[bits]++;

xbits = 0;

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

f = tree[n].Freq;

s->opt_len += (ulg)f * (unsigned)(bits + xbits);

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

}

if (overflow == 0) return;

Tracev((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 (s->bl_count[bits] == 0) bits--;

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

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

s->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 = s->bl_count[bits];

while (n != 0) {

m = s->heap[--h];

if (m > max_code) continue;

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

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

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

tree[m].Len = (ush)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, bl_count)

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

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

ushf *bl_count; /* number of codes at each bit length */

{

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

unsigned 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++) {

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

next_code[bits] = (ush)code;

}

/* 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<<MAX_BITS)-1,

"inconsistent bit counts");

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 = (ush)bi_reverse(next_code[len]++, len);

Tracecv(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(s, desc)

deflate_state *s;

tree_desc *desc; /* the tree descriptor */

{

ct_data *tree = desc->dyn_tree;

const ct_data *stree = desc->stat_desc->static_tree;

int elems = desc->stat_desc->elems;

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

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

int node; /* new node being created */

/* 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.

s->heap_len = 0, s->heap_max = HEAP_SIZE;

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

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

s->heap[++(s->heap_len)] = max_code = n;

s->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 (s->heap_len < 2) {

node = s->heap[++(s->heap_len)] = (max_code < 2 ? ++max_code : 0);

tree[node].Freq = 1;

s->depth[node] = 0;

s->opt_len--; if (stree) s->static_len -= stree[node].Len;

/* node 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 = s->heap_len/2; n >= 1; n--) pqdownheap(s, tree, n);

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

* frequent nodes.

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

do {

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

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

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

s->heap[--(s->heap_max)] = m;

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

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

s->depth[node] = (uch)((s->depth[n] >= s->depth[m] ?

s->depth[n] : s->depth[m]) + 1);

tree[n].Dad = tree[m].Dad = (ush)node;

#ifdef DUMP_BL_TREE

if (tree == s->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 */

s->heap[SMALLEST] = node++;

pqdownheap(s, tree, SMALLEST);

} while (s->heap_len >= 2);

s->heap[--(s->heap_max)] = s->heap[SMALLEST];

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

* generate the bit lengths.

gen_bitlen(s, (tree_desc *)desc);

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

gen_codes ((ct_data *)tree, max_code, s->bl_count);

}

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

* Scan a literal or distance tree to determine the frequencies of the codes

* in the bit length tree.

local void scan_tree (s, tree, max_code)

deflate_state *s;

ct_data *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) {

s->bl_tree[curlen].Freq += count;

} else if (curlen != 0) {

if (curlen != prevlen) s->bl_tree[curlen].Freq++;

s->bl_tree[REP_3_6].Freq++;

} else if (count <= 10) {

s->bl_tree[REPZ_3_10].Freq++;

} else {

s->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 (s, tree, max_code)

deflate_state *s;

ct_data *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(s, curlen, s->bl_tree); } while (--count != 0);

} else if (curlen != 0) {

if (curlen != prevlen) {

send_code(s, curlen, s->bl_tree); count--;

}

Assert(count >= 3 && count <= 6, " 3_6?");

send_code(s, REP_3_6, s->bl_tree); send_bits(s, count-3, 2);

} else if (count <= 10) {

send_code(s, REPZ_3_10, s->bl_tree); send_bits(s, count-3, 3);

} else {

send_code(s, REPZ_11_138, s->bl_tree); send_bits(s, 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(s)

deflate_state *s;

{

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(s, (ct_data *)s->dyn_ltree, s->l_desc.max_code);

scan_tree(s, (ct_data *)s->dyn_dtree, s->d_desc.max_code);

/* Build the bit length tree: */

build_tree(s, (tree_desc *)(&(s->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 (s->bl_tree[bl_order[max_blindex]].Len != 0) break;

}

/* Update opt_len to include the bit length tree and counts */

s->opt_len += 3*((ulg)max_blindex+1) + 5+5+4;

Tracev((stderr, "\ndyn trees: dyn %ld, stat %ld",

s->opt_len, s->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(s, lcodes, dcodes, blcodes)

deflate_state *s;

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

send_bits(s, dcodes-1, 5);

send_bits(s, 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(s, s->bl_tree[bl_order[rank]].Len, 3);

}

Tracev((stderr, "\nbl tree: sent %ld", s->bits_sent));

send_tree(s, (ct_data *)s->dyn_ltree, lcodes-1); /* literal tree */

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

send_tree(s, (ct_data *)s->dyn_dtree, dcodes-1); /* distance tree */

Tracev((stderr, "\ndist tree: sent %ld", s->bits_sent));

}

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

* Send a stored block

void ZLIB_INTERNAL _tr_stored_block(s, buf, stored_len, last)

deflate_state *s;

charf *buf; /* input block */

ulg stored_len; /* length of input block */

int last; /* one if this is the last block for a file */

{

send_bits(s, (STORED_BLOCK<<1)+last, 3); /* send block type */

bi_windup(s); /* align on byte boundary */

put_short(s, (ush)stored_len);

put_short(s, (ush)~stored_len);

zmemcpy(s->pending_buf + s->pending, (Bytef *)buf, stored_len);

s->pending += stored_len;

#ifdef ZLIB_DEBUG

s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;

s->compressed_len += (stored_len + 4) << 3;

s->bits_sent += 2*16;

s->bits_sent += stored_len<<3;

#endif

}

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

* Flush the bits in the bit buffer to pending output (leaves at most 7 bits)

void ZLIB_INTERNAL _tr_flush_bits(s)

deflate_state *s;

{

bi_flush(s);

}

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

* Send one empty static block to give enough lookahead for inflate.

* This takes 10 bits, of which 7 may remain in the bit buffer.

void ZLIB_INTERNAL _tr_align(s)

deflate_state *s;

{

send_bits(s, STATIC_TREES<<1, 3);

send_code(s, END_BLOCK, static_ltree);

#ifdef ZLIB_DEBUG

s->compressed_len += 10L; /* 3 for block type, 7 for EOB */

#endif

bi_flush(s);

}

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

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

* trees or store, and write out the encoded block.

void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)

deflate_state *s;

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

ulg stored_len; /* length of input block */

int last; /* one if this is the last block for a file */

{

ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */

int max_blindex = 0; /* index of last bit length code of non zero freq */

/* Build the Huffman trees unless a stored block is forced */

if (s->level > 0) {

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

if (s->strm->data_type == Z_UNKNOWN)

s->strm->data_type = detect_data_type(s);

/* Construct the literal and distance trees */

build_tree(s, (tree_desc *)(&(s->l_desc)));

Tracev((stderr, "\nlit data: dyn %ld, stat %ld", s->opt_len,

s->static_len));

build_tree(s, (tree_desc *)(&(s->d_desc)));

Tracev((stderr, "\ndist data: dyn %ld, stat %ld", s->opt_len,

s->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(s);

/* Determine the best encoding. Compute the block lengths in bytes. */

opt_lenb = (s->opt_len+3+7)>>3;

static_lenb = (s->static_len+3+7)>>3;

Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",

opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,

s->last_lit));

if (static_lenb <= opt_lenb) opt_lenb = static_lenb;

} else {

Assert(buf != (char*)0, "lost buf");

opt_lenb = static_lenb = stored_len + 5; /* force a stored block */

}

#ifdef FORCE_STORED

if (buf != (char*)0) { /* force stored block */

#else

if (stored_len+4 <= opt_lenb && buf != (char*)0) {

/* 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.

_tr_stored_block(s, buf, stored_len, last);

#ifdef FORCE_STATIC

} else if (static_lenb >= 0) { /* force static trees */

#else

} else if (s->strategy == Z_FIXED || static_lenb == opt_lenb) {

#endif

send_bits(s, (STATIC_TREES<<1)+last, 3);

compress_block(s, (const ct_data *)static_ltree,

(const ct_data *)static_dtree);

#ifdef ZLIB_DEBUG

s->compressed_len += 3 + s->static_len;

#endif

} else {

send_bits(s, (DYN_TREES<<1)+last, 3);

send_all_trees(s, s->l_desc.max_code+1, s->d_desc.max_code+1,

max_blindex+1);

compress_block(s, (const ct_data *)s->dyn_ltree,

(const ct_data *)s->dyn_dtree);

#ifdef ZLIB_DEBUG

s->compressed_len += 3 + s->opt_len;

#endif

}

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

/* The above check is made mod 2^32, for files larger than 512 MB

* and uLong implemented on 32 bits.

init_block(s);

if (last) {

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cpython/Modules/zlib/trees.c at 3.5 · python/cpython · GitHub

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