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gzip.c
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gzip.c
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/* vi: set sw=4 ts=4: */
/*
* Gzip implementation for busybox
*
* Based on GNU gzip Copyright (C) 1992-1993 Jean-loup Gailly.
*
* Originally adjusted for busybox by Charles P. Wright <cpw@unix.asb.com>
* "this is a stripped down version of gzip I put into busybox, it does
* only standard in to standard out with -9 compression. It also requires
* the zcat module for some important functions."
*
* Adjusted further by Erik Andersen <andersee@debian.org>
* to support files as well as stdin/stdout, and to generally behave itself wrt
* command line handling.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
/* These defines are very important for BusyBox. Without these,
* huge chunks of ram are pre-allocated making the BusyBox bss
* size Freaking Huge(tm), which is a bad thing.*/
#define SMALL_MEM
#define DYN_ALLOC
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <signal.h>
#include <utime.h>
#include <ctype.h>
#include <sys/types.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/fcntl.h>
#include <time.h>
#include "busybox.h"
#define memzero(s, n) memset ((void *)(s), 0, (n))
#ifndef RETSIGTYPE
# define RETSIGTYPE void
#endif
typedef unsigned char uch;
typedef unsigned short ush;
typedef unsigned long ulg;
/* Return codes from gzip */
#define OK 0
#define ERROR 1
#define WARNING 2
/* Compression methods (see algorithm.doc) */
/* Only STORED and DEFLATED are supported by this BusyBox module */
#define STORED 0
/* methods 4 to 7 reserved */
#define DEFLATED 8
static int method; /* compression method */
/* To save memory for 16 bit systems, some arrays are overlaid between
* the various modules:
* deflate: prev+head window d_buf l_buf outbuf
* unlzw: tab_prefix tab_suffix stack inbuf outbuf
* For compression, input is done in window[]. For decompression, output
* is done in window except for unlzw.
*/
#ifndef INBUFSIZ
# ifdef SMALL_MEM
# define INBUFSIZ 0x2000 /* input buffer size */
# else
# define INBUFSIZ 0x8000 /* input buffer size */
# endif
#endif
#define INBUF_EXTRA 64 /* required by unlzw() */
#ifndef OUTBUFSIZ
# ifdef SMALL_MEM
# define OUTBUFSIZ 8192 /* output buffer size */
# else
# define OUTBUFSIZ 16384 /* output buffer size */
# endif
#endif
#define OUTBUF_EXTRA 2048 /* required by unlzw() */
#ifndef DIST_BUFSIZE
# ifdef SMALL_MEM
# define DIST_BUFSIZE 0x2000 /* buffer for distances, see trees.c */
# else
# define DIST_BUFSIZE 0x8000 /* buffer for distances, see trees.c */
# endif
#endif
#ifdef DYN_ALLOC
# define DECLARE(type, array, size) static type * array
# define ALLOC(type, array, size) { \
array = (type*)calloc((size_t)(((size)+1L)/2), 2*sizeof(type)); \
if (array == NULL) error_msg(memory_exhausted); \
}
# define FREE(array) {if (array != NULL) free(array), array=NULL;}
#else
# define DECLARE(type, array, size) static type array[size]
# define ALLOC(type, array, size)
# define FREE(array)
#endif
#define tab_suffix window
#define tab_prefix prev /* hash link (see deflate.c) */
#define head (prev+WSIZE) /* hash head (see deflate.c) */
static long bytes_in; /* number of input bytes */
#define isize bytes_in
/* for compatibility with old zip sources (to be cleaned) */
typedef int file_t; /* Do not use stdio */
#define NO_FILE (-1) /* in memory compression */
#define PACK_MAGIC "\037\036" /* Magic header for packed files */
#define GZIP_MAGIC "\037\213" /* Magic header for gzip files, 1F 8B */
#define OLD_GZIP_MAGIC "\037\236" /* Magic header for gzip 0.5 = freeze 1.x */
#define LZH_MAGIC "\037\240" /* Magic header for SCO LZH Compress files */
#define PKZIP_MAGIC "\120\113\003\004" /* Magic header for pkzip files */
/* gzip flag byte */
#define ASCII_FLAG 0x01 /* bit 0 set: file probably ascii text */
#define CONTINUATION 0x02 /* bit 1 set: continuation of multi-part gzip file */
#define EXTRA_FIELD 0x04 /* bit 2 set: extra field present */
#define ORIG_NAME 0x08 /* bit 3 set: original file name present */
#define COMMENT 0x10 /* bit 4 set: file comment present */
#define RESERVED 0xC0 /* bit 6,7: reserved */
/* internal file attribute */
#define UNKNOWN 0xffff
#define BINARY 0
#define ASCII 1
#ifndef WSIZE
# define WSIZE 0x8000 /* window size--must be a power of two, and */
#endif /* at least 32K for zip's deflate method */
#define MIN_MATCH 3
#define MAX_MATCH 258
/* The minimum and maximum match lengths */
#define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
/* Minimum amount of lookahead, except at the end of the input file.
* See deflate.c for comments about the MIN_MATCH+1.
*/
#define MAX_DIST (WSIZE-MIN_LOOKAHEAD)
/* In order to simplify the code, particularly on 16 bit machines, match
* distances are limited to MAX_DIST instead of WSIZE.
*/
/* put_byte is used for the compressed output */
#define put_byte(c) {outbuf[outcnt++]=(uch)(c); if (outcnt==OUTBUFSIZ)\
flush_outbuf();}
/* Output a 16 bit value, lsb first */
#define put_short(w) \
{ if (outcnt < OUTBUFSIZ-2) { \
outbuf[outcnt++] = (uch) ((w) & 0xff); \
outbuf[outcnt++] = (uch) ((ush)(w) >> 8); \
} else { \
put_byte((uch)((w) & 0xff)); \
put_byte((uch)((ush)(w) >> 8)); \
} \
}
/* Output a 32 bit value to the bit stream, lsb first */
#define put_long(n) { \
put_short((n) & 0xffff); \
put_short(((ulg)(n)) >> 16); \
}
#define seekable() 0 /* force sequential output */
#define translate_eol 0 /* no option -a yet */
/* Diagnostic functions */
#ifdef DEBUG
# define Assert(cond,msg) {if(!(cond)) error_msg(msg);}
# define Trace(x) fprintf x
# define Tracev(x) {if (verbose) fprintf x ;}
# define Tracevv(x) {if (verbose>1) fprintf x ;}
# define Tracec(c,x) {if (verbose && (c)) fprintf x ;}
# define Tracecv(c,x) {if (verbose>1 && (c)) fprintf x ;}
#else
# define Assert(cond,msg)
# define Trace(x)
# define Tracev(x)
# define Tracevv(x)
# define Tracec(c,x)
# define Tracecv(c,x)
#endif
#define WARN(msg) {if (!quiet) fprintf msg ; \
if (exit_code == OK) exit_code = WARNING;}
#ifndef MAX_PATH_LEN
# define MAX_PATH_LEN 1024 /* max pathname length */
#endif
/* from zip.c: */
static int zip (int in, int out);
static int file_read (char *buf, unsigned size);
/* from gzip.c */
static RETSIGTYPE CDECL abort_gzip (void);
/* from deflate.c */
static void lm_init (ush * flags);
static ulg deflate (void);
/* from trees.c */
static void ct_init (ush * attr, int *methodp);
static int ct_tally (int dist, int lc);
static ulg flush_block (char *buf, ulg stored_len, int eof);
/* from bits.c */
static void bi_init (file_t zipfile);
static void send_bits (int value, int length);
static unsigned bi_reverse (unsigned value, int length);
static void bi_windup (void);
static void copy_block (char *buf, unsigned len, int header);
static int (*read_buf) (char *buf, unsigned size);
/* from util.c: */
static void flush_outbuf (void);
/* lzw.h -- define the lzw functions.
* Copyright (C) 1992-1993 Jean-loup Gailly.
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License, see the file COPYING.
*/
#if !defined(OF) && defined(lint)
# include "gzip.h"
#endif
#ifndef BITS
# define BITS 16
#endif
#define INIT_BITS 9 /* Initial number of bits per code */
#define BIT_MASK 0x1f /* Mask for 'number of compression bits' */
/* Mask 0x20 is reserved to mean a fourth header byte, and 0x40 is free.
* It's a pity that old uncompress does not check bit 0x20. That makes
* extension of the format actually undesirable because old compress
* would just crash on the new format instead of giving a meaningful
* error message. It does check the number of bits, but it's more
* helpful to say "unsupported format, get a new version" than
* "can only handle 16 bits".
*/
/* tailor.h -- target dependent definitions
* Copyright (C) 1992-1993 Jean-loup Gailly.
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License, see the file COPYING.
*/
/* The target dependent definitions should be defined here only.
* The target dependent functions should be defined in tailor.c.
*/
/* Common defaults */
#ifndef OS_CODE
# define OS_CODE 0x03 /* assume Unix */
#endif
#ifndef PATH_SEP
# define PATH_SEP '/'
#endif
#ifndef OPTIONS_VAR
# define OPTIONS_VAR "GZIP"
#endif
#ifndef Z_SUFFIX
# define Z_SUFFIX ".gz"
#endif
#ifdef MAX_EXT_CHARS
# define MAX_SUFFIX MAX_EXT_CHARS
#else
# define MAX_SUFFIX 30
#endif
/* global buffers */
DECLARE(uch, inbuf, INBUFSIZ + INBUF_EXTRA);
DECLARE(uch, outbuf, OUTBUFSIZ + OUTBUF_EXTRA);
DECLARE(ush, d_buf, DIST_BUFSIZE);
DECLARE(uch, window, 2L * WSIZE);
DECLARE(ush, tab_prefix, 1L << BITS);
static int crc_table_empty = 1;
static int foreground; /* set if program run in foreground */
static int method = DEFLATED; /* compression method */
static int exit_code = OK; /* program exit code */
static int part_nb; /* number of parts in .gz file */
static long time_stamp; /* original time stamp (modification time) */
static long ifile_size; /* input file size, -1 for devices (debug only) */
static char z_suffix[MAX_SUFFIX + 1]; /* default suffix (can be set with --suffix) */
static int z_len; /* strlen(z_suffix) */
static char ifname[MAX_PATH_LEN]; /* input file name */
static char ofname[MAX_PATH_LEN]; /* output file name */
static int ifd; /* input file descriptor */
static int ofd; /* output file descriptor */
static unsigned insize; /* valid bytes in inbuf */
static unsigned outcnt; /* bytes in output buffer */
/* ========================================================================
* Signal and error handler.
*/
static void CDECL abort_gzip()
{
exit(ERROR);
}
/* ===========================================================================
* Clear input and output buffers
*/
static void clear_bufs(void)
{
outcnt = 0;
insize = 0;
bytes_in = 0L;
}
static void write_error_msg()
{
fprintf(stderr, "\n");
perror("");
abort_gzip();
}
/* ===========================================================================
* Does the same as write(), but also handles partial pipe writes and checks
* for error return.
*/
static void write_buf(int fd, void *buf, unsigned cnt)
{
unsigned n;
while ((n = write(fd, buf, cnt)) != cnt) {
if (n == (unsigned) (-1)) {
write_error_msg();
}
cnt -= n;
buf = (void *) ((char *) buf + n);
}
}
/* ===========================================================================
* Run a set of bytes through the crc shift register. If s is a NULL
* pointer, then initialize the crc shift register contents instead.
* Return the current crc in either case.
*/
static ulg updcrc(uch *s, unsigned n)
{
static ulg crc = (ulg) 0xffffffffL; /* shift register contents */
register ulg c; /* temporary variable */
static unsigned long crc_32_tab[256];
if (crc_table_empty) {
unsigned long csr; /* crc shift register */
unsigned long e=0; /* polynomial exclusive-or pattern */
int i; /* counter for all possible eight bit values */
int k; /* byte being shifted into crc apparatus */
/* terms of polynomial defining this crc (except x^32): */
static const int p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
/* Make exclusive-or pattern from polynomial (0xedb88320) */
for (i = 0; i < sizeof(p)/sizeof(int); i++)
e |= 1L << (31 - p[i]);
/* Compute and print table of CRC's, five per line */
crc_32_tab[0] = 0x00000000L;
for (i = 1; i < 256; i++) {
csr = i;
/* The idea to initialize the register with the byte instead of
* zero was stolen from Haruhiko Okumura's ar002
*/
for (k = 8; k; k--)
csr = csr & 1 ? (csr >> 1) ^ e : csr >> 1;
crc_32_tab[i]=csr;
}
}
if (s == NULL) {
c = 0xffffffffL;
} else {
c = crc;
if (n)
do {
c = crc_32_tab[((int) c ^ (*s++)) & 0xff] ^ (c >> 8);
} while (--n);
}
crc = c;
return c ^ 0xffffffffL; /* (instead of ~c for 64-bit machines) */
}
/* bits.c -- output variable-length bit strings
* Copyright (C) 1992-1993 Jean-loup Gailly
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License, see the file COPYING.
*/
/*
* PURPOSE
*
* Output variable-length bit strings. Compression can be done
* to a file or to memory. (The latter is not supported in this version.)
*
* DISCUSSION
*
* The PKZIP "deflate" file format interprets compressed file data
* as a sequence of bits. Multi-bit strings in the file may cross
* byte boundaries without restriction.
*
* The first bit of each byte is the low-order bit.
*
* The routines in this file allow a variable-length bit value to
* be output right-to-left (useful for literal values). For
* left-to-right output (useful for code strings from the tree routines),
* the bits must have been reversed first with bi_reverse().
*
* For in-memory compression, the compressed bit stream goes directly
* into the requested output buffer. The input data is read in blocks
* by the mem_read() function. The buffer is limited to 64K on 16 bit
* machines.
*
* INTERFACE
*
* void bi_init (FILE *zipfile)
* Initialize the bit string routines.
*
* void send_bits (int value, int length)
* Write out a bit string, taking the source bits right to
* left.
*
* int bi_reverse (int value, int length)
* Reverse the bits of a bit string, taking the source bits left to
* right and emitting them right to left.
*
* void bi_windup (void)
* Write out any remaining bits in an incomplete byte.
*
* void copy_block(char *buf, unsigned len, int header)
* Copy a stored block to the zip file, storing first the length and
* its one's complement if requested.
*
*/
/* ===========================================================================
* Local data used by the "bit string" routines.
*/
static file_t zfile; /* output gzip file */
static unsigned short bi_buf;
/* Output buffer. bits are inserted starting at the bottom (least significant
* bits).
*/
#define Buf_size (8 * 2*sizeof(char))
/* Number of bits used within bi_buf. (bi_buf might be implemented on
* more than 16 bits on some systems.)
*/
static int bi_valid;
/* Current input function. Set to mem_read for in-memory compression */
#ifdef DEBUG
ulg bits_sent; /* bit length of the compressed data */
#endif
/* ===========================================================================
* Initialize the bit string routines.
*/
static void bi_init(file_t zipfile)
{
zfile = zipfile;
bi_buf = 0;
bi_valid = 0;
#ifdef DEBUG
bits_sent = 0L;
#endif
/* Set the defaults for file compression. They are set by memcompress
* for in-memory compression.
*/
if (zfile != NO_FILE) {
read_buf = file_read;
}
}
/* ===========================================================================
* Send a value on a given number of bits.
* IN assertion: length <= 16 and value fits in length bits.
*/
static void send_bits(int value, int length)
{
#ifdef DEBUG
Tracev((stderr, " l %2d v %4x ", length, value));
Assert(length > 0 && length <= 15, "invalid length");
bits_sent += (ulg) length;
#endif
/* 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 (bi_valid > (int) Buf_size - length) {
bi_buf |= (value << bi_valid);
put_short(bi_buf);
bi_buf = (ush) value >> (Buf_size - bi_valid);
bi_valid += length - Buf_size;
} else {
bi_buf |= value << bi_valid;
bi_valid += length;
}
}
/* ===========================================================================
* Reverse the first len bits of a code, using straightforward code (a faster
* method would use a table)
* IN assertion: 1 <= len <= 15
*/
static unsigned bi_reverse(unsigned code, int len)
{
register unsigned res = 0;
do {
res |= code & 1;
code >>= 1, res <<= 1;
} while (--len > 0);
return res >> 1;
}
/* ===========================================================================
* Write out any remaining bits in an incomplete byte.
*/
static void bi_windup()
{
if (bi_valid > 8) {
put_short(bi_buf);
} else if (bi_valid > 0) {
put_byte(bi_buf);
}
bi_buf = 0;
bi_valid = 0;
#ifdef DEBUG
bits_sent = (bits_sent + 7) & ~7;
#endif
}
/* ===========================================================================
* Copy a stored block to the zip file, storing first the length and its
* one's complement if requested.
*/
static void copy_block(char *buf, unsigned len, int header)
{
bi_windup(); /* align on byte boundary */
if (header) {
put_short((ush) len);
put_short((ush) ~ len);
#ifdef DEBUG
bits_sent += 2 * 16;
#endif
}
#ifdef DEBUG
bits_sent += (ulg) len << 3;
#endif
while (len--) {
put_byte(*buf++);
}
}
/* deflate.c -- compress data using the deflation algorithm
* Copyright (C) 1992-1993 Jean-loup Gailly
* This is free software; you can redistribute it and/or modify it under the
* terms of the GNU General Public License, see the file COPYING.
*/
/*
* PURPOSE
*
* Identify new text as repetitions of old text within a fixed-
* length sliding window trailing behind the new text.
*
* DISCUSSION
*
* The "deflation" process depends on being able to identify portions
* of the input text which are identical to earlier input (within a
* sliding window trailing behind the input currently being processed).
*
* The most straightforward technique turns out to be the fastest for
* most input files: try all possible matches and select the longest.
* The key feature of this algorithm is that insertions into the string
* dictionary are very simple and thus fast, and deletions are avoided
* completely. Insertions are performed at each input character, whereas
* string matches are performed only when the previous match ends. So it
* is preferable to spend more time in matches to allow very fast string
* insertions and avoid deletions. The matching algorithm for small
* strings is inspired from that of Rabin & Karp. A brute force approach
* is used to find longer strings when a small match has been found.
* A similar algorithm is used in comic (by Jan-Mark Wams) and freeze
* (by Leonid Broukhis).
* A previous version of this file used a more sophisticated algorithm
* (by Fiala and Greene) which is guaranteed to run in linear amortized
* time, but has a larger average cost, uses more memory and is patented.
* However the F&G algorithm may be faster for some highly redundant
* files if the parameter max_chain_length (described below) is too large.
*
* ACKNOWLEDGEMENTS
*
* The idea of lazy evaluation of matches is due to Jan-Mark Wams, and
* I found it in 'freeze' written by Leonid Broukhis.
* Thanks to many info-zippers for bug reports and testing.
*
* REFERENCES
*
* APPNOTE.TXT documentation file in PKZIP 1.93a distribution.
*
* A description of the Rabin and Karp algorithm is given in the book
* "Algorithms" by R. Sedgewick, Addison-Wesley, p252.
*
* Fiala,E.R., and Greene,D.H.
* Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595
*
* INTERFACE
*
* void lm_init (int pack_level, ush *flags)
* Initialize the "longest match" routines for a new file
*
* ulg deflate (void)
* Processes a new input file and return its compressed length. Sets
* the compressed length, crc, deflate flags and internal file
* attributes.
*/
/* ===========================================================================
* Configuration parameters
*/
/* Compile with MEDIUM_MEM to reduce the memory requirements or
* with SMALL_MEM to use as little memory as possible. Use BIG_MEM if the
* entire input file can be held in memory (not possible on 16 bit systems).
* Warning: defining these symbols affects HASH_BITS (see below) and thus
* affects the compression ratio. The compressed output
* is still correct, and might even be smaller in some cases.
*/
#ifdef SMALL_MEM
# define HASH_BITS 13 /* Number of bits used to hash strings */
#endif
#ifdef MEDIUM_MEM
# define HASH_BITS 14
#endif
#ifndef HASH_BITS
# define HASH_BITS 15
/* For portability to 16 bit machines, do not use values above 15. */
#endif
/* To save space (see unlzw.c), we overlay prev+head with tab_prefix and
* window with tab_suffix. Check that we can do this:
*/
#if (WSIZE<<1) > (1<<BITS)
# error cannot overlay window with tab_suffix and prev with tab_prefix0
#endif
#if HASH_BITS > BITS-1
# error cannot overlay head with tab_prefix1
#endif
#define HASH_SIZE (unsigned)(1<<HASH_BITS)
#define HASH_MASK (HASH_SIZE-1)
#define WMASK (WSIZE-1)
/* HASH_SIZE and WSIZE must be powers of two */
#define NIL 0
/* Tail of hash chains */
#define FAST 4
#define SLOW 2
/* speed options for the general purpose bit flag */
#ifndef TOO_FAR
# define TOO_FAR 4096
#endif
/* Matches of length 3 are discarded if their distance exceeds TOO_FAR */
/* ===========================================================================
* Local data used by the "longest match" routines.
*/
typedef ush Pos;
typedef unsigned IPos;
/* A Pos is an index in the character window. We use short instead of int to
* save space in the various tables. IPos is used only for parameter passing.
*/
/* DECLARE(uch, window, 2L*WSIZE); */
/* Sliding window. Input bytes are read into the second half of the window,
* and move to the first half later to keep a dictionary of at least WSIZE
* bytes. With this organization, matches are limited to a distance of
* WSIZE-MAX_MATCH bytes, but this ensures that IO is always
* performed with a length multiple of the block size. Also, it limits
* the window size to 64K, which is quite useful on MSDOS.
* To do: limit the window size to WSIZE+BSZ if SMALL_MEM (the code would
* be less efficient).
*/
/* DECLARE(Pos, prev, WSIZE); */
/* Link to older string with same hash index. To limit the size of this
* array to 64K, this link is maintained only for the last 32K strings.
* An index in this array is thus a window index modulo 32K.
*/
/* DECLARE(Pos, head, 1<<HASH_BITS); */
/* Heads of the hash chains or NIL. */
static const ulg window_size = (ulg) 2 * WSIZE;
/* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the
* input file length plus MIN_LOOKAHEAD.
*/
static long block_start;
/* window position at the beginning of the current output block. Gets
* negative when the window is moved backwards.
*/
static unsigned ins_h; /* hash index of string to be inserted */
#define H_SHIFT ((HASH_BITS+MIN_MATCH-1)/MIN_MATCH)
/* Number of bits by which ins_h and del_h must be shifted at each
* input step. It must be such that after MIN_MATCH steps, the oldest
* byte no longer takes part in the hash key, that is:
* H_SHIFT * MIN_MATCH >= HASH_BITS
*/
static unsigned int prev_length;
/* Length of the best match at previous step. Matches not greater than this
* are discarded. This is used in the lazy match evaluation.
*/
static unsigned strstart; /* start of string to insert */
static unsigned match_start; /* start of matching string */
static int eofile; /* flag set at end of input file */
static unsigned lookahead; /* number of valid bytes ahead in window */
static const unsigned max_chain_length=4096;
/* To speed up deflation, hash chains are never searched beyond this length.
* A higher limit improves compression ratio but degrades the speed.
*/
static const unsigned int max_lazy_match=258;
/* Attempt to find a better match only when the current match is strictly
* smaller than this value. This mechanism is used only for compression
* levels >= 4.
*/
#define max_insert_length max_lazy_match
/* Insert new strings in the hash table only if the match length
* is not greater than this length. This saves time but degrades compression.
* max_insert_length is used only for compression levels <= 3.
*/
static const unsigned good_match=32;
/* Use a faster search when the previous match is longer than this */
/* Values for max_lazy_match, good_match and max_chain_length, depending on
* the desired pack level (0..9). The values given below have been tuned to
* exclude worst case performance for pathological files. Better values may be
* found for specific files.
*/
static const int nice_match=258; /* Stop searching when current match exceeds this */
/* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4
* For deflate_fast() (levels <= 3) good is ignored and lazy has a different
* meaning.
*/
#define EQUAL 0
/* result of memcmp for equal strings */
/* ===========================================================================
* Prototypes for local functions.
*/
static void fill_window (void);
static int longest_match (IPos cur_match);
#ifdef DEBUG
static void check_match (IPos start, IPos match, int length);
#endif
/* ===========================================================================
* Update a hash value with the given input byte
* IN assertion: all calls to to UPDATE_HASH are made with consecutive
* input characters, so that a running hash key can be computed from the
* previous key instead of complete recalculation each time.
*/
#define UPDATE_HASH(h,c) (h = (((h)<<H_SHIFT) ^ (c)) & HASH_MASK)
/* ===========================================================================
* Insert string s in the dictionary and set match_head to the previous head
* of the hash chain (the most recent string with same hash key). Return
* the previous length of the hash chain.
* IN assertion: all calls to to INSERT_STRING are made with consecutive
* input characters and the first MIN_MATCH bytes of s are valid
* (except for the last MIN_MATCH-1 bytes of the input file).
*/
#define INSERT_STRING(s, match_head) \
(UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]), \
prev[(s) & WMASK] = match_head = head[ins_h], \
head[ins_h] = (s))
/* ===========================================================================
* Initialize the "longest match" routines for a new file
*/
static void lm_init(ush *flags)
{
register unsigned j;
/* Initialize the hash table. */
memzero((char *) head, HASH_SIZE * sizeof(*head));
/* prev will be initialized on the fly */
*flags |= SLOW;
/* ??? reduce max_chain_length for binary files */
strstart = 0;
block_start = 0L;
lookahead = read_buf((char *) window,
sizeof(int) <= 2 ? (unsigned) WSIZE : 2 * WSIZE);
if (lookahead == 0 || lookahead == (unsigned) EOF) {
eofile = 1, lookahead = 0;
return;
}
eofile = 0;
/* Make sure that we always have enough lookahead. This is important
* if input comes from a device such as a tty.
*/
while (lookahead < MIN_LOOKAHEAD && !eofile)
fill_window();
ins_h = 0;
for (j = 0; j < MIN_MATCH - 1; j++)
UPDATE_HASH(ins_h, window[j]);
/* If lookahead < MIN_MATCH, ins_h is garbage, but this is
* not important since only literal bytes will be emitted.
*/
}
/* ===========================================================================
* Set match_start to the longest match starting at the given string and
* return its length. Matches shorter or equal to prev_length are discarded,
* in which case the result is equal to prev_length and match_start is
* garbage.
* IN assertions: cur_match is the head of the hash chain for the current
* string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1
*/
/* For MSDOS, OS/2 and 386 Unix, an optimized version is in match.asm or
* match.s. The code is functionally equivalent, so you can use the C version
* if desired.
*/
static int longest_match(IPos cur_match)
{
unsigned chain_length = max_chain_length; /* max hash chain length */
register uch *scan = window + strstart; /* current string */
register uch *match; /* matched string */
register int len; /* length of current match */
int best_len = prev_length; /* best match length so far */
IPos limit =
strstart > (IPos) MAX_DIST ? strstart - (IPos) MAX_DIST : NIL;
/* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0.
*/
/* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
* It is easy to get rid of this optimization if necessary.
*/
#if HASH_BITS < 8 || MAX_MATCH != 258
# error Code too clever
#endif
register uch *strend = window + strstart + MAX_MATCH;
register uch scan_end1 = scan[best_len - 1];
register uch scan_end = scan[best_len];
/* Do not waste too much time if we already have a good match: */
if (prev_length >= good_match) {
chain_length >>= 2;
}
Assert(strstart <= window_size - MIN_LOOKAHEAD,
"insufficient lookahead");
do {
Assert(cur_match < strstart, "no future");
match = window + cur_match;
/* Skip to next match if the match length cannot increase
* or if the match length is less than 2:
*/
if (match[best_len] != scan_end ||
match[best_len - 1] != scan_end1 ||
*match != *scan || *++match != scan[1])
continue;
/* The check at best_len-1 can be removed because it will be made
* again later. (This heuristic is not always a win.)
* It is not necessary to compare scan[2] and match[2] since they
* are always equal when the other bytes match, given that
* the hash keys are equal and that HASH_BITS >= 8.
*/
scan += 2, match++;
/* We check for insufficient lookahead only every 8th comparison;
* the 256th check will be made at strstart+258.
*/
do {
} while (*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
scan < strend);
len = MAX_MATCH - (int) (strend - scan);
scan = strend - MAX_MATCH;
if (len > best_len) {
match_start = cur_match;
best_len = len;
if (len >= nice_match)
break;
scan_end1 = scan[best_len - 1];
scan_end = scan[best_len];
}
} while ((cur_match = prev[cur_match & WMASK]) > limit
&& --chain_length != 0);
return best_len;
}
#ifdef DEBUG
/* ===========================================================================
* Check that the match at match_start is indeed a match.
*/
static void check_match(IPos start, IPos match, int length)
{
/* check that the match is indeed a match */
if (memcmp((char *) window + match,
(char *) window + start, length) != EQUAL) {
fprintf(stderr,
" start %d, match %d, length %d\n", start, match, length);
error_msg("invalid match");
}
if (verbose > 1) {
fprintf(stderr, "\\[%d,%d]", start - match, length);
do {
putc(window[start++], stderr);
} while (--length != 0);
}
}
#else