godot/thirdparty/zlib/trees.c

/* trees.c -- output deflated data using Huffman coding
 * Copyright (C) 1995-2024 Jean-loup Gailly
 * 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 …
/* Bit length codes must not exceed MAX_BL_BITS bits */

#define END_BLOCK …
/* end of block literal code */

#define REP_3_6 …
/* repeat previous bit length 3-6 times (2 bits of repeat count) */

#define REPZ_3_10 …
/* repeat a zero length 3-10 times  (3 bits of repeat count) */

#define REPZ_11_138 …
/* 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 */
   = …;

local const int extra_dbits[D_CODES] /* extra bits for each distance code */
   = …;

local const int extra_blbits[BL_CODES]/* extra bits for each bit length code */
   = …;

local const uch bl_order[BL_CODES]
   = …;
/* 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 …

#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 { … };

#ifdef NO_INIT_GLOBAL_POINTERS
#define TCONST
#else
#define TCONST …
#endif

local TCONST static_tree_desc static_l_desc = …;

local TCONST static_tree_desc static_d_desc = …;

local TCONST static_tree_desc static_bl_desc = …;

/* ===========================================================================
 * Output a short LSB first on the stream.
 * IN assertion: there is enough room in pendingBuf.
 */
#define put_short(s, w) …

/* ===========================================================================
 * Reverse the first len bits of a code, using straightforward code (a faster
 * method would use a table)
 * IN assertion: 1 <= len <= 15
 */
local unsigned bi_reverse(unsigned code, int len) { … }

/* ===========================================================================
 * Flush the bit buffer, keeping at most 7 bits in it.
 */
local void bi_flush(deflate_state *s) { … }

/* ===========================================================================
 * Flush the bit buffer and align the output on a byte boundary
 */
local void bi_windup(deflate_state *s) { … }

/* ===========================================================================
 * 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(ct_data *tree, int max_code, ushf *bl_count) { … }

#ifdef GEN_TREES_H
local void gen_trees_header(void);
#endif

#ifndef ZLIB_DEBUG
#define send_code(s, c, tree) …
   /* Send a code of the given tree. c and tree must not have side effects */

#else /* !ZLIB_DEBUG */
#define send_code …
#endif

/* ===========================================================================
 * 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(deflate_state *s, int value, int length) {
    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) …
#endif /* ZLIB_DEBUG */


/* the arguments must not have side effects */

/* ===========================================================================
 * Initialize the various 'constant' tables.
 */
local void tr_static_init(void) { … }

/* ===========================================================================
 * Generate the file trees.h describing the static trees.
 */
#ifdef GEN_TREES_H
#  ifndef ZLIB_DEBUG
#    include <stdio.h>
#  endif

#define SEPARATOR …

void gen_trees_header(void) {
    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 a new block.
 */
local void init_block(deflate_state *s) { … }

/* ===========================================================================
 * Initialize the tree data structures for a new zlib stream.
 */
void ZLIB_INTERNAL _tr_init(deflate_state *s) { … }

#define SMALLEST …
/* 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) …

/* ===========================================================================
 * 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) …

/* ===========================================================================
 * 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(deflate_state *s, ct_data *tree, int k) { … }

/* ===========================================================================
 * 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(deflate_state *s, tree_desc *desc) { … }

#ifdef DUMP_BL_TREE
#  include <stdio.h>
#endif

/* ===========================================================================
 * 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(deflate_state *s, tree_desc *desc) { … }

/* ===========================================================================
 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree.
 */
local void scan_tree(deflate_state *s, ct_data *tree, int max_code) { … }

/* ===========================================================================
 * Send a literal or distance tree in compressed form, using the codes in
 * bl_tree.
 */
local void send_tree(deflate_state *s, ct_data *tree, int max_code) { … }

/* ===========================================================================
 * 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(deflate_state *s) { … }

/* ===========================================================================
 * 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(deflate_state *s, int lcodes, int dcodes,
                          int blcodes) { … }

/* ===========================================================================
 * Send a stored block
 */
void ZLIB_INTERNAL _tr_stored_block(deflate_state *s, charf *buf,
                                    ulg stored_len, int last) { … }

/* ===========================================================================
 * Flush the bits in the bit buffer to pending output (leaves at most 7 bits)
 */
void ZLIB_INTERNAL _tr_flush_bits(deflate_state *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(deflate_state *s) { … }

/* ===========================================================================
 * Send the block data compressed using the given Huffman trees
 */
local void compress_block(deflate_state *s, const ct_data *ltree,
                          const ct_data *dtree) { … }

/* ===========================================================================
 * Check if the data type is TEXT or BINARY, using the following algorithm:
 * - TEXT if the two conditions below are satisfied:
 *    a) There are no non-portable control characters belonging to the
 *       "block list" (0..6, 14..25, 28..31).
 *    b) There is at least one printable character belonging to the
 *       "allow list" (9 {TAB}, 10 {LF}, 13 {CR}, 32..255).
 * - BINARY otherwise.
 * - The following partially-portable control characters form a
 *   "gray list" that is ignored in this detection algorithm:
 *   (7 {BEL}, 8 {BS}, 11 {VT}, 12 {FF}, 26 {SUB}, 27 {ESC}).
 * IN assertion: the fields Freq of dyn_ltree are set.
 */
local int detect_data_type(deflate_state *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(deflate_state *s, charf *buf,
                                   ulg stored_len, int last) { … }

/* ===========================================================================
 * Save the match info and tally the frequency counts. Return true if
 * the current block must be flushed.
 */
int ZLIB_INTERNAL _tr_tally(deflate_state *s, unsigned dist, unsigned lc) { … }