gunzip.c

i386的bootloader源码grub

   the distance codes.  Subsequent tables are also less than or equal to
   those sizes.  These values may be adjusted either when all of the
   codes are shorter than that, in which case the longest code length in
   bits is used, or when the shortest code is *longer* than the requested
   table size, in which case the length of the shortest code in bits is
   used.

   There are two different values for the two tables, since they code a
   different number of possibilities each.  The literal/length table
   codes 286 possible values, or in a flat code, a little over eight
   bits.  The distance table codes 30 possible values, or a little less
   than five bits, flat.  The optimum values for speed end up being
   about one bit more than those, so lbits is 8+1 and dbits is 5+1.
   The optimum values may differ though from machine to machine, and
   possibly even between compilers.  Your mileage may vary.
 */


static int lbits = 9;		/* bits in base literal/length lookup table */
static int dbits = 6;		/* bits in base distance lookup table */


/* If BMAX needs to be larger than 16, then h and x[] should be ulg. */
#define BMAX 16			/* maximum bit length of any code (16 for explode) */
#define N_MAX 288		/* maximum number of codes in any set */


static unsigned hufts;		/* track memory usage */


/* Macros for inflate() bit peeking and grabbing.
   The usage is:

        NEEDBITS(j)
        x = b & mask_bits[j];
        DUMPBITS(j)

   where NEEDBITS makes sure that b has at least j bits in it, and
   DUMPBITS removes the bits from b.  The macros use the variable k
   for the number of bits in b.  Normally, b and k are register
   variables for speed, and are initialized at the beginning of a
   routine that uses these macros from a global bit buffer and count.

   If we assume that EOB will be the longest code, then we will never
   ask for bits with NEEDBITS that are beyond the end of the stream.
   So, NEEDBITS should not read any more bytes than are needed to
   meet the request.  Then no bytes need to be "returned" to the buffer
   at the end of the last block.

   However, this assumption is not true for fixed blocks--the EOB code
   is 7 bits, but the other literal/length codes can be 8 or 9 bits.
   (The EOB code is shorter than other codes because fixed blocks are
   generally short.  So, while a block always has an EOB, many other
   literal/length codes have a significantly lower probability of
   showing up at all.)  However, by making the first table have a
   lookup of seven bits, the EOB code will be found in that first
   lookup, and so will not require that too many bits be pulled from
   the stream.
 */

static ulg bb;			/* bit buffer */
static unsigned bk;		/* bits in bit buffer */

static ush mask_bits[] =
{
  0x0000,
  0x0001, 0x0003, 0x0007, 0x000f, 0x001f, 0x003f, 0x007f, 0x00ff,
  0x01ff, 0x03ff, 0x07ff, 0x0fff, 0x1fff, 0x3fff, 0x7fff, 0xffff
};

#define NEEDBITS(n) do {while(k<(n)){b|=((ulg)get_byte())<<k;k+=8;}} while (0)
#define DUMPBITS(n) do {b>>=(n);k-=(n);} while (0)

#define INBUFSIZ  0x2000

static uch inbuf[INBUFSIZ];
static int bufloc;

static int
get_byte (void)
{
  if (filepos == gzip_data_offset || bufloc == INBUFSIZ)
    {
      bufloc = 0;
      grub_read (inbuf, INBUFSIZ);
    }

  return inbuf[bufloc++];
}

/* decompression global pointers */
static struct huft *tl;		/* literal/length code table */
static struct huft *td;		/* distance code table */
static int bl;			/* lookup bits for tl */
static int bd;			/* lookup bits for td */


/* more function prototypes */
static int huft_build (unsigned *, unsigned, unsigned, ush *, ush *,
		       struct huft **, int *);
static int inflate_codes_in_window (void);


/* Given a list of code lengths and a maximum table size, make a set of
   tables to decode that set of codes.  Return zero on success, one if
   the given code set is incomplete (the tables are still built in this
   case), two if the input is invalid (all zero length codes or an
   oversubscribed set of lengths), and three if not enough memory. */

static int
huft_build (unsigned *b,	/* code lengths in bits (all assumed <= BMAX) */
	    unsigned n,		/* number of codes (assumed <= N_MAX) */
	    unsigned s,		/* number of simple-valued codes (0..s-1) */
	    ush * d,		/* list of base values for non-simple codes */
	    ush * e,		/* list of extra bits for non-simple codes */
	    struct huft **t,	/* result: starting table */
	    int *m)		/* maximum lookup bits, returns actual */
{
  unsigned a;			/* counter for codes of length k */
  unsigned c[BMAX + 1];		/* bit length count table */
  unsigned f;			/* i repeats in table every f entries */
  int g;			/* maximum code length */
  int h;			/* table level */
  register unsigned i;		/* counter, current code */
  register unsigned j;		/* counter */
  register int k;		/* number of bits in current code */
  int l;			/* bits per table (returned in m) */
  register unsigned *p;		/* pointer into c[], b[], or v[] */
  register struct huft *q;	/* points to current table */
  struct huft r;		/* table entry for structure assignment */
  struct huft *u[BMAX];		/* table stack */
  unsigned v[N_MAX];		/* values in order of bit length */
  register int w;		/* bits before this table == (l * h) */
  unsigned x[BMAX + 1];		/* bit offsets, then code stack */
  unsigned *xp;			/* pointer into x */
  int y;			/* number of dummy codes added */
  unsigned z;			/* number of entries in current table */

  /* Generate counts for each bit length */
  memset ((char *) c, 0, sizeof (c));
  p = b;
  i = n;
  do
    {
      c[*p]++;			/* assume all entries <= BMAX */
      p++;			/* Can't combine with above line (Solaris bug) */
    }
  while (--i);
  if (c[0] == n)		/* null input--all zero length codes */
    {
      *t = (struct huft *) NULL;
      *m = 0;
      return 0;
    }

  /* Find minimum and maximum length, bound *m by those */
  l = *m;
  for (j = 1; j <= BMAX; j++)
    if (c[j])
      break;
  k = j;			/* minimum code length */
  if ((unsigned) l < j)
    l = j;
  for (i = BMAX; i; i--)
    if (c[i])
      break;
  g = i;			/* maximum code length */
  if ((unsigned) l > i)
    l = i;
  *m = l;

  /* Adjust last length count to fill out codes, if needed */
  for (y = 1 << j; j < i; j++, y <<= 1)
    if ((y -= c[j]) < 0)
      return 2;			/* bad input: more codes than bits */
  if ((y -= c[i]) < 0)
    return 2;
  c[i] += y;

  /* Generate starting offsets into the value table for each length */
  x[1] = j = 0;
  p = c + 1;
  xp = x + 2;
  while (--i)
    {				/* note that i == g from above */
      *xp++ = (j += *p++);
    }

  /* Make a table of values in order of bit lengths */
  p = b;
  i = 0;
  do
    {
      if ((j = *p++) != 0)
	v[x[j]++] = i;
    }
  while (++i < n);

  /* Generate the Huffman codes and for each, make the table entries */
  x[0] = i = 0;			/* first Huffman code is zero */
  p = v;			/* grab values in bit order */
  h = -1;			/* no tables yet--level -1 */
  w = -l;			/* bits decoded == (l * h) */
  u[0] = (struct huft *) NULL;	/* just to keep compilers happy */
  q = (struct huft *) NULL;	/* ditto */
  z = 0;			/* ditto */

  /* go through the bit lengths (k already is bits in shortest code) */
  for (; k <= g; k++)
    {
      a = c[k];
      while (a--)
	{
	  /* here i is the Huffman code of length k bits for value *p */
	  /* make tables up to required level */
	  while (k > w + l)
	    {
	      h++;
	      w += l;		/* previous table always l bits */

	      /* compute minimum size table less than or equal to l bits */
	      z = (z = g - w) > (unsigned) l ? l : z;	/* upper limit on table size */
	      if ((f = 1 << (j = k - w)) > a + 1)	/* try a k-w bit table */
		{		/* too few codes for k-w bit table */
		  f -= a + 1;	/* deduct codes from patterns left */
		  xp = c + k;
		  while (++j < z)	/* try smaller tables up to z bits */
		    {
		      if ((f <<= 1) <= *++xp)
			break;	/* enough codes to use up j bits */
		      f -= *xp;	/* else deduct codes from patterns */
		    }
		}
	      z = 1 << j;	/* table entries for j-bit table */

	      /* allocate and link in new table */
	      q = (struct huft *) linalloc ((z + 1) * sizeof (struct huft));

	      hufts += z + 1;	/* track memory usage */
	      *t = q + 1;	/* link to list for huft_free() */
	      *(t = &(q->v.t)) = (struct huft *) NULL;
	      u[h] = ++q;	/* table starts after link */

	      /* connect to last table, if there is one */
	      if (h)
		{
		  x[h] = i;	/* save pattern for backing up */
		  r.b = (uch) l;	/* bits to dump before this table */
		  r.e = (uch) (16 + j);		/* bits in this table */
		  r.v.t = q;	/* pointer to this table */
		  j = i >> (w - l);	/* (get around Turbo C bug) */
		  u[h - 1][j] = r;	/* connect to last table */
		}
	    }

	  /* set up table entry in r */
	  r.b = (uch) (k - w);
	  if (p >= v + n)
	    r.e = 99;		/* out of values--invalid code */
	  else if (*p < s)
	    {
	      r.e = (uch) (*p < 256 ? 16 : 15);		/* 256 is end-of-block code */
	      r.v.n = (ush) (*p);	/* simple code is just the value */
	      p++;		/* one compiler does not like *p++ */
	    }
	  else
	    {
	      r.e = (uch) e[*p - s];	/* non-simple--look up in lists */
	      r.v.n = d[*p++ - s];
	    }

	  /* fill code-like entries with r */
	  f = 1 << (k - w);
	  for (j = i >> w; j < z; j += f)
	    q[j] = r;

	  /* backwards increment the k-bit code i */
	  for (j = 1 << (k - 1); i & j; j >>= 1)
	    i ^= j;
	  i ^= j;

	  /* backup over finished tables */
	  while ((i & ((1 << w) - 1)) != x[h])
	    {
	      h--;		/* don't need to update q */
	      w -= l;
	    }
	}
    }

  /* Return true (1) if we were given an incomplete table */
  return y != 0 && g != 1;
}


/*
 *  inflate (decompress) the codes in a deflated (compressed) block.
 *  Return an error code or zero if it all goes ok.
 */

static unsigned inflate_n, inflate_d;

static int
inflate_codes_in_window (void)
{
  register unsigned e;		/* table entry flag/number of extra bits */
  unsigned n, d;		/* length and index for copy */
  unsigned w;			/* current window position */
  struct huft *t;		/* pointer to table entry */
  unsigned ml, md;		/* masks for bl and bd bits */
  register ulg b;		/* bit buffer */
  register unsigned k;		/* number of bits in bit buffer */

  /* make local copies of globals */
  d = inflate_d;
  n = inflate_n;
  b = bb;			/* initialize bit buffer */
  k = bk;
  w = wp;			/* initialize window position */

  /* inflate the coded data */
  ml = mask_bits[bl];		/* precompute masks for speed */
  md = mask_bits[bd];
  for (;;)			/* do until end of block */
    {
      if (!code_state)
	{
	  NEEDBITS ((unsigned) bl);
	  if ((e = (t = tl + ((unsigned) b & ml))->e) > 16)
	    do
	      {
		if (e == 99)
		  {
		    errnum = ERR_BAD_GZIP_DATA;
		    return 0;
		  }
		DUMPBITS (t->b);
		e -= 16;
		NEEDBITS (e);
	      }
	    while ((e = (t = t->v.t + ((unsigned) b & mask_bits[e]))->e) > 16);
	  DUMPBITS (t->b);

	  if (e == 16)		/* then it's a literal */
	    {
	      slide[w++] = (uch) t->v.n;
	      if (w == WSIZE)
		break;
	    }
	  else
	    /* it's an EOB or a length */
	    {
	      /* exit if end of block */
	      if (e == 15)
		{
		  block_len = 0;
		  break;
		}

	      /* get length of block to copy */
	      NEEDBITS (e);
	      n = t->v.n + ((unsigned) b & mask_bits[e]);
	      DUMPBITS (e);

	      /* decode distance of block to copy */
	      NEEDBITS ((unsigned) bd);
	      if ((e = (t = td + ((unsigned) b & md))->e) > 16)
		do
		  {
		    if (e == 99)
		      {
			errnum = ERR_BAD_GZIP_DATA;
			return 0;
		      }
		    DUMPBITS (t->b);
		    e -= 16;
		    NEEDBITS (e);
		  }
		while ((e = (t = t->v.t + ((unsigned) b & mask_bits[e]))->e)
		       > 16);
	      DUMPBITS (t->b);
	      NEEDBITS (e);
	      d = w - t->v.n - ((unsigned) b & mask_bits[e]);
	      DUMPBITS (e);
	      code_state++;
	    }
	}

      if (code_state)
	{
	  /* do the copy */
	  do
	    {
	      n -= (e = (e = WSIZE - ((d &= WSIZE - 1) > w ? d : w)) > n ? n
		    : e);
	      if (w - d >= e)
		{
		  memmove (slide + w, slide + d, e);
		  w += e;
		  d += e;
		}
	      else
		/* purposefully use the overlap for extra copies here!! */
		{
		  while (e--)
		    slide[w++] = slide[d++];
		}
	      if (w == WSIZE)
		break;
	    }
	  while (n);