zlib/inftrees.c

/* inftrees.c -- generate Huffman trees for efficient decoding
 * Copyright (C) 1995 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h 
 */

#include "zutil.h"
#include "inftrees.h"

struct internal_state  {int dummy;}; /* for buggy compilers */

/* simplify the use of the inflate_huft type with some defines */
#define base more.Base
#define next more.Next
#define exop word.what.Exop
#define bits word.what.Bits


local int huft_build OF((
    uIntf *,            /* code lengths in bits */
    uInt,               /* number of codes */
    uInt,               /* number of "simple" codes */
    uIntf *,            /* list of base values for non-simple codes */
    uIntf *,            /* list of extra bits for non-simple codes */
    inflate_huft * FAR*,/* result: starting table */
    uIntf *,            /* maximum lookup bits (returns actual) */
    z_stream *));       /* for zalloc function */

local voidp falloc OF((
    voidp,              /* opaque pointer (not used) */
    uInt,               /* number of items */
    uInt));             /* size of item */

local void ffree OF((
    voidp q,            /* opaque pointer (not used) */
    voidp p));          /* what to free (not used) */

/* Tables for deflate from PKZIP's appnote.txt. */
local uInt 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};
        /* actually lengths - 2; also see note #13 above about 258 */
local uInt 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, 192, 192}; /* 192==invalid */
local uInt 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};
local uInt 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
   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.
 */


/* If BMAX needs to be larger than 16, then h and x[] should be uLong. */
#define BMAX 15         /* maximum bit length of any code */
#define N_MAX 288       /* maximum number of codes in any set */

#ifdef DEBUG
  uInt inflate_hufts;
#endif

local int huft_build(b, n, s, d, e, t, m, zs)
uIntf *b;               /* code lengths in bits (all assumed <= BMAX) */
uInt n;                 /* number of codes (assumed <= N_MAX) */
uInt s;                 /* number of simple-valued codes (0..s-1) */
uIntf *d;               /* list of base values for non-simple codes */
uIntf *e;               /* list of extra bits for non-simple codes */  
inflate_huft * FAR *t;  /* result: starting table */
uIntf *m;               /* maximum lookup bits, returns actual */
z_stream *zs;           /* for zalloc function */
/* Given a list of code lengths and a maximum table size, make a set of
   tables to decode that set of codes.  Return Z_OK on success, Z_BUF_ERROR
   if the given code set is incomplete (the tables are still built in this
   case), Z_DATA_ERROR if the input is invalid (all zero length codes or an
   over-subscribed set of lengths), or Z_MEM_ERROR if not enough memory. */
{

  uInt a;                       /* counter for codes of length k */
  uInt c[BMAX+1];               /* bit length count table */
  uInt f;                       /* i repeats in table every f entries */
  int g;                        /* maximum code length */
  int h;                        /* table level */
  register uInt i;              /* counter, current code */
  register uInt j;              /* counter */
  register int k;               /* number of bits in current code */
  int l;                        /* bits per table (returned in m) */
  register uIntf *p;            /* pointer into c[], b[], or v[] */
  inflate_huft *q;              /* points to current table */
  struct inflate_huft_s r;      /* table entry for structure assignment */
  inflate_huft *u[BMAX];        /* table stack */
  uInt v[N_MAX];                /* values in order of bit length */
  register int w;               /* bits before this table == (l * h) */
  uInt x[BMAX+1];               /* bit offsets, then code stack */
  uIntf *xp;                    /* pointer into x */
  int y;                        /* number of dummy codes added */
  uInt z;                       /* number of entries in current table */


  /* Generate counts for each bit length */
  p = c;
#define C0 *p++ = 0;
#define C2 C0 C0 C0 C0
#define C4 C2 C2 C2 C2
  C4                            /* clear c[]--assume BMAX+1 is 16 */
  p = b;  i = n;
  do {
    c[*p++]++;                  /* assume all entries <= BMAX */
  } while (--i);
  if (c[0] == n)                /* null input--all zero length codes */
  {
    *t = (inflate_huft *)Z_NULL;
    *m = 0;
    return Z_OK;
  }


  /* 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 ((uInt)l < j)
    l = j;
  for (i = BMAX; i; i--)
    if (c[i])
      break;
  g = i;                        /* maximum code length */
  if ((uInt)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 Z_DATA_ERROR;
  if ((y -= c[i]) < 0)
    return Z_DATA_ERROR;
  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] = (inflate_huft *)Z_NULL;        /* just to keep compilers happy */
  q = (inflate_huft *)Z_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) > (uInt)l ? l : z;      /* table size upper limit */
        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;
          if (j < z)
            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 */
        if ((q = (inflate_huft *)ZALLOC
             (zs,z + 1,sizeof(inflate_huft))) == Z_NULL)
        {
          if (h)
            inflate_trees_free(u[0], zs);
          return Z_MEM_ERROR;   /* not enough memory */
        }
#ifdef DEBUG
        inflate_hufts += z + 1;
#endif
        *t = q + 1;             /* link to list for huft_free() */
        *(t = &(q->next)) = Z_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.bits = (Byte)l;     /* bits to dump before this table */
          r.exop = (Byte)j;     /* bits in this table */
          r.next = 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.bits = (Byte)(k - w);
      if (p >= v + n)
        r.exop = 128 + 64;      /* out of values--invalid code */
      else if (*p < s)
      {
        r.exop = (Byte)(*p < 256 ? 0 : 32 + 64);     /* 256 is end-of-block */
        r.base = *p++;          /* simple code is just the value */
      }
      else
      {
        r.exop = (Byte)e[*p - s] + 16 + 64; /* non-simple--look up in lists */
        r.base = 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 Z_BUF_ERROR if we were given an incomplete table */
  return y != 0 && g != 1 ? Z_BUF_ERROR : Z_OK;
}


int inflate_trees_bits(c, bb, tb, z)
uIntf *c;               /* 19 code lengths */
uIntf *bb;              /* bits tree desired/actual depth */
inflate_huft * FAR *tb; /* bits tree result */
z_stream *z;            /* for zfree function */
{
  int r;

  r = huft_build(c, 19, 19, (uIntf*)Z_NULL, (uIntf*)Z_NULL, tb, bb, z);
  if (r == Z_DATA_ERROR)
    z->msg = "oversubscribed dynamic bit lengths tree";
  else if (r == Z_BUF_ERROR)
  {
    inflate_trees_free(*tb, z);
    z->msg = "incomplete dynamic bit lengths tree";
    r = Z_DATA_ERROR;
  }
  return r;
}


int inflate_trees_dynamic(nl, nd, c, bl, bd, tl, td, z)
uInt nl;                /* number of literal/length codes */
uInt nd;                /* number of distance codes */
uIntf *c;               /* that many (total) code lengths */
uIntf *bl;              /* literal desired/actual bit depth */
uIntf *bd;              /* distance desired/actual bit depth */
inflate_huft * FAR *tl; /* literal/length tree result */
inflate_huft * FAR *td; /* distance tree result */
z_stream *z;            /* for zfree function */
{
  int r;

  /* build literal/length tree */
  if ((r = huft_build(c, nl, 257, cplens, cplext, tl, bl, z)) != Z_OK)
  {
    if (r == Z_DATA_ERROR)
      z->msg = "oversubscribed literal/length tree";
    else if (r == Z_BUF_ERROR)
    {
      inflate_trees_free(*tl, z);
      z->msg = "incomplete literal/length tree";
      r = Z_DATA_ERROR;
    }
    return r;
  }

  /* build distance tree */
  if ((r = huft_build(c + nl, nd, 0, cpdist, cpdext, td, bd, z)) != Z_OK)
  {
    if (r == Z_DATA_ERROR)
      z->msg = "oversubscribed literal/length tree";
    else if (r == Z_BUF_ERROR) {
#ifdef PKZIP_BUG_WORKAROUND
      r = Z_OK;
    }
#else
      inflate_trees_free(*td, z);
      z->msg = "incomplete literal/length tree";
      r = Z_DATA_ERROR;
    }
    inflate_trees_free(*tl, z);
    return r;
#endif
  }

  /* done */
  return Z_OK;
}


/* build fixed tables only once--keep them here */
local int fixed_lock = 0;
local int fixed_built = 0;
#define FIXEDH 530      /* number of hufts used by fixed tables */
local uInt fixed_left = FIXEDH;
local inflate_huft fixed_mem[FIXEDH];
local uInt fixed_bl;
local uInt fixed_bd;
local inflate_huft *fixed_tl;
local inflate_huft *fixed_td;


local voidp falloc(q, n, s)
voidp q;        /* opaque pointer (not used) */
uInt n;         /* number of items */
uInt s;         /* size of item */
{
  Assert(s == sizeof(inflate_huft) && n <= fixed_left,
         "inflate_trees falloc overflow");
  if (q) s++; /* to make some compilers happy */
  fixed_left -= n;
  return (voidp)(fixed_mem + fixed_left);
}


local void ffree(q, p)
voidp q;
voidp p;
{
  Assert(0, "inflate_trees ffree called!");
  if (q) q = p; /* to make some compilers happy */
}


int inflate_trees_fixed(bl, bd, tl, td)
uIntf *bl;               /* literal desired/actual bit depth */
uIntf *bd;               /* distance desired/actual bit depth */
inflate_huft * FAR *tl;  /* literal/length tree result */
inflate_huft * FAR *td;  /* distance tree result */
{
  /* build fixed tables if not built already--lock out other instances */
  while (++fixed_lock > 1)
    fixed_lock--;
  if (!fixed_built)
  {
    int k;              /* temporary variable */
    unsigned c[288];    /* length list for huft_build */
    z_stream z;         /* for falloc function */

    /* set up fake z_stream for memory routines */
    z.zalloc = falloc;
    z.zfree = ffree;
    z.opaque = Z_NULL;

    /* literal table */
    for (k = 0; k < 144; k++)
      c[k] = 8;
    for (; k < 256; k++)
      c[k] = 9;
    for (; k < 280; k++)
      c[k] = 7;
    for (; k < 288; k++)
      c[k] = 8;
    fixed_bl = 7;
    huft_build(c, 288, 257, cplens, cplext, &fixed_tl, &fixed_bl, &z);

    /* distance table */
    for (k = 0; k < 30; k++)
      c[k] = 5;
    fixed_bd = 5;
    huft_build(c, 30, 0, cpdist, cpdext, &fixed_td, &fixed_bd, &z);

    /* done */
    fixed_built = 1;
  }
  fixed_lock--;
  *bl = fixed_bl;
  *bd = fixed_bd;
  *tl = fixed_tl;
  *td = fixed_td;
  return Z_OK;
}


int inflate_trees_free(t, z)
inflate_huft *t;        /* table to free */
z_stream *z;            /* for zfree function */
/* Free the malloc'ed tables built by huft_build(), which makes a linked
   list of the tables it made, with the links in a dummy first entry of
   each table. */
{
  register inflate_huft *p, *q;

  /* Go through linked list, freeing from the malloced (t[-1]) address. */
  p = t;
  while (p != Z_NULL)
  {
    q = (--p)->next;
    ZFREE(z,p);
    p = q;
  } 
  return Z_OK;
}