gunzip.c

i386的bootloader源码grub

/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 1999  Free Software Foundation, Inc.
 *
 *  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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * Most of this file was originally the source file "inflate.c", written
 * by Mark Adler.  It has been very heavily modified.  In particular, the
 * original would run through the whole file at once, and this version can
 * be stopped and restarted on any boundary during the decompression process.
 *
 * The license and header comments that file are included here.
 */

/* inflate.c -- Not copyrighted 1992 by Mark Adler
   version c10p1, 10 January 1993 */

/* You can do whatever you like with this source file, though I would
   prefer that if you modify it and redistribute it that you include
   comments to that effect with your name and the date.  Thank you.
 */

/*
   Inflate deflated (PKZIP's method 8 compressed) data.  The compression
   method searches for as much of the current string of bytes (up to a
   length of 258) in the previous 32K bytes.  If it doesn't find any
   matches (of at least length 3), it codes the next byte.  Otherwise, it
   codes the length of the matched string and its distance backwards from
   the current position.  There is a single Huffman code that codes both
   single bytes (called "literals") and match lengths.  A second Huffman
   code codes the distance information, which follows a length code.  Each
   length or distance code actually represents a base value and a number
   of "extra" (sometimes zero) bits to get to add to the base value.  At
   the end of each deflated block is a special end-of-block (EOB) literal/
   length code.  The decoding process is basically: get a literal/length
   code; if EOB then done; if a literal, emit the decoded byte; if a
   length then get the distance and emit the referred-to bytes from the
   sliding window of previously emitted data.

   There are (currently) three kinds of inflate blocks: stored, fixed, and
   dynamic.  The compressor deals with some chunk of data at a time, and
   decides which method to use on a chunk-by-chunk basis.  A chunk might
   typically be 32K or 64K.  If the chunk is uncompressible, then the
   "stored" method is used.  In this case, the bytes are simply stored as
   is, eight bits per byte, with none of the above coding.  The bytes are
   preceded by a count, since there is no longer an EOB code.

   If the data is compressible, then either the fixed or dynamic methods
   are used.  In the dynamic method, the compressed data is preceded by
   an encoding of the literal/length and distance Huffman codes that are
   to be used to decode this block.  The representation is itself Huffman
   coded, and so is preceded by a description of that code.  These code
   descriptions take up a little space, and so for small blocks, there is
   a predefined set of codes, called the fixed codes.  The fixed method is
   used if the block codes up smaller that way (usually for quite small
   chunks), otherwise the dynamic method is used.  In the latter case, the
   codes are customized to the probabilities in the current block, and so
   can code it much better than the pre-determined fixed codes.

   The Huffman codes themselves are decoded using a mutli-level table
   lookup, in order to maximize the speed of decoding plus the speed of
   building the decoding tables.  See the comments below that precede the
   lbits and dbits tuning parameters.
 */


/*
   Notes beyond the 1.93a appnote.txt:

   1. Distance pointers never point before the beginning of the output
      stream.
   2. Distance pointers can point back across blocks, up to 32k away.
   3. There is an implied maximum of 7 bits for the bit length table and
      15 bits for the actual data.
   4. If only one code exists, then it is encoded using one bit.  (Zero
      would be more efficient, but perhaps a little confusing.)  If two
      codes exist, they are coded using one bit each (0 and 1).
   5. There is no way of sending zero distance codes--a dummy must be
      sent if there are none.  (History: a pre 2.0 version of PKZIP would
      store blocks with no distance codes, but this was discovered to be
      too harsh a criterion.)  Valid only for 1.93a.  2.04c does allow
      zero distance codes, which is sent as one code of zero bits in
      length.
   6. There are up to 286 literal/length codes.  Code 256 represents the
      end-of-block.  Note however that the static length tree defines
      288 codes just to fill out the Huffman codes.  Codes 286 and 287
      cannot be used though, since there is no length base or extra bits
      defined for them.  Similarly, there are up to 30 distance codes.
      However, static trees define 32 codes (all 5 bits) to fill out the
      Huffman codes, but the last two had better not show up in the data.
   7. Unzip can check dynamic Huffman blocks for complete code sets.
      The exception is that a single code would not be complete (see #4).
   8. The five bits following the block type is really the number of
      literal codes sent minus 257.
   9. Length codes 8,16,16 are interpreted as 13 length codes of 8 bits
      (1+6+6).  Therefore, to output three times the length, you output
      three codes (1+1+1), whereas to output four times the same length,
      you only need two codes (1+3).  Hmm.
  10. In the tree reconstruction algorithm, Code = Code + Increment
      only if BitLength(i) is not zero.  (Pretty obvious.)
  11. Correction: 4 Bits: # of Bit Length codes - 4     (4 - 19)
  12. Note: length code 284 can represent 227-258, but length code 285
      really is 258.  The last length deserves its own, short code
      since it gets used a lot in very redundant files.  The length
      258 is special since 258 - 3 (the min match length) is 255.
  13. The literal/length and distance code bit lengths are read as a
      single stream of lengths.  It is possible (and advantageous) for
      a repeat code (16, 17, or 18) to go across the boundary between
      the two sets of lengths.
 */

#ifndef NO_DECOMPRESSION

#include "shared.h"

#include "filesys.h"

/* so we can disable decompression  */
int no_decompression = 0;

/* used to tell if "read" should be redirected to "gunzip_read" */
int compressed_file;

/* internal variables only */
static int gzip_data_offset;
static int gzip_filepos;
static int gzip_filemax;
static int gzip_fsmax;
static int saved_filepos;
static unsigned long gzip_crc;

/* internal extra variables for use of inflate code */
static int block_type;
static int block_len;
static int last_block;
static int code_state;


/* Function prototypes */
static void initialize_tables (void);

/*
 *  Linear allocator.
 */

static unsigned long linalloc_topaddr;

static void *
linalloc (int size)
{
  linalloc_topaddr = (linalloc_topaddr - size) & ~3;
  return (void *) linalloc_topaddr;
}

static void
reset_linalloc (void)
{
  linalloc_topaddr = RAW_ADDR ((mbi.mem_upper << 10) + 0x100000);
}


/* internal variable swap function */
static void
gunzip_swap_values (void)
{
  register int itmp;

  /* swap filepos */
  itmp = filepos;
  filepos = gzip_filepos;
  gzip_filepos = itmp;

  /* swap filemax */
  itmp = filemax;
  filemax = gzip_filemax;
  gzip_filemax = itmp;

  /* swap fsmax */
  itmp = fsmax;
  fsmax = gzip_fsmax;
  gzip_fsmax = itmp;
}


/* internal function for eating variable-length header fields */
static int
bad_field (int len)
{
  char ch = 1;
  int not_retval = 1;

  do
    {
      if (len >= 0)
	{
	  if (!(len--))
	    break;
	}
      else
	{
	  if (!ch)
	    break;
	}
    }
  while ((not_retval = grub_read (&ch, 1)) == 1);

  return (!not_retval);
}


/* Little-Endian defines for the 2-byte magic number for gzip files */
#define GZIP_HDR_LE      0x8B1F
#define OLD_GZIP_HDR_LE  0x9E1F

/* Compression methods (see algorithm.doc) */
#define STORED      0
#define COMPRESSED  1
#define PACKED      2
#define LZHED       3
/* methods 4 to 7 reserved */
#define DEFLATED    8
#define MAX_METHODS 9

/* 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 ENCRYPTED    0x20	/* bit 5 set: file is encrypted */
#define RESERVED     0xC0	/* bit 6,7:   reserved */

#define UNSUPP_FLAGS (CONTINUATION|ENCRYPTED|RESERVED)

/* inflate block codes */
#define INFLATE_STORED    0
#define INFLATE_FIXED     1
#define INFLATE_DYNAMIC   2

typedef unsigned char uch;
typedef unsigned short ush;
typedef unsigned long ulg;

/*
 *  Window Size
 *
 *  This must be a power of two, and at least 32K for zip's deflate method
 */

#define WSIZE 0x8000


int
gunzip_test_header (void)
{
  unsigned char buf[10];
  
  /* "compressed_file" is already reset to zero by this point */

  /*
   *  This checks if the file is gzipped.  If a problem occurs here
   *  (other than a real error with the disk) then we don't think it
   *  is a compressed file, and simply mark it as such.
   */
  if (no_decompression
      || grub_read (buf, 10) != 10
      || ((*((unsigned short *) buf) != GZIP_HDR_LE)
	  && (*((unsigned short *) buf) != OLD_GZIP_HDR_LE)))
    {
      filepos = 0;
      return ! errnum;
    }

  /*
   *  This does consistency checking on the header data.  If a
   *  problem occurs from here on, then we have corrupt or otherwise
   *  bad data, and the error should be reported to the user.
   */
  if (buf[2] != DEFLATED
      || (buf[3] & UNSUPP_FLAGS)
      || ((buf[3] & EXTRA_FIELD)
	  && (grub_read (buf, 2) != 2
	      || bad_field (*((unsigned short *) buf))))
      || ((buf[3] & ORIG_NAME) && bad_field (-1))
      || ((buf[3] & COMMENT) && bad_field (-1)))
    {
      if (! errnum)
	errnum = ERR_BAD_GZIP_HEADER;
      
      return 0;
    }

  gzip_data_offset = filepos;
  
  filepos = filemax - 8;
  
  if (grub_read (buf, 8) != 8)
    {
      if (! errnum)
	errnum = ERR_BAD_GZIP_HEADER;
      
      return 0;
    }

  gzip_crc = *((unsigned long *) buf);
  gzip_fsmax = gzip_filemax = *((unsigned long *) (buf + 4));

  initialize_tables ();

  compressed_file = 1;
  gunzip_swap_values ();
  /*
   *  Now "gzip_*" values refer to the compressed data.
   */

  filepos = 0;

  return 1;
}


/* Huffman code lookup table entry--this entry is four bytes for machines
   that have 16-bit pointers (e.g. PC's in the small or medium model).
   Valid extra bits are 0..13.  e == 15 is EOB (end of block), e == 16
   means that v is a literal, 16 < e < 32 means that v is a pointer to
   the next table, which codes e - 16 bits, and lastly e == 99 indicates
   an unused code.  If a code with e == 99 is looked up, this implies an
   error in the data. */
struct huft
{
  uch e;			/* number of extra bits or operation */
  uch b;			/* number of bits in this code or subcode */
  union
    {
      ush n;			/* literal, length base, or distance base */
      struct huft *t;		/* pointer to next level of table */
    }
  v;
};


/* The inflate algorithm uses a sliding 32K byte window on the uncompressed
   stream to find repeated byte strings.  This is implemented here as a
   circular buffer.  The index is updated simply by incrementing and then
   and'ing with 0x7fff (32K-1). */
/* It is left to other modules to supply the 32K area.  It is assumed
   to be usable as if it were declared "uch slide[32768];" or as just
   "uch *slide;" and then malloc'ed in the latter case.  The definition
   must be in unzip.h, included above. */


/* sliding window in uncompressed data */
static uch slide[WSIZE];

/* current position in slide */
static unsigned wp;


/* Tables for deflate from PKZIP's appnote.txt. */
static unsigned bitorder[] =
{				/* Order of the bit length code lengths */
  16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
static ush cplens[] =
{				/* Copy lengths for literal codes 257..285 */
  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
  35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
	/* note: see note #13 above about the 258 in this list. */
static ush cplext[] =
{				/* Extra bits for literal codes 257..285 */
  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, 99, 99};	/* 99==invalid */
static ush cpdist[] =
{				/* Copy offsets for distance codes 0..29 */
  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
  257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
  8193, 12289, 16385, 24577};
static ush cpdext[] =
{				/* Extra bits for distance codes */
  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};


/*
   Huffman code decoding is performed using a multi-level table lookup.
   The fastest way to decode is to simply build a lookup table whose
   size is determined by the longest code.  However, the time it takes
   to build this table can also be a factor if the data being decoded
   is not very long.  The most common codes are necessarily the
   shortest codes, so those codes dominate the decoding time, and hence
   the speed.  The idea is you can have a shorter table that decodes the
   shorter, more probable codes, and then point to subsidiary tables for
   the longer codes.  The time it costs to decode the longer codes is
   then traded against the time it takes to make longer tables.

   This results of this trade are in the variables lbits and dbits
   below.  lbits is the number of bits the first level table for literal/
   length codes can decode in one step, and dbits is the same thing for