~drizzle-trunk/drizzle/development

/* Copyright (C) 2000-2006 MySQL AB

   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; version 2 of the License.

   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 */

	/* Functions to compressed records */

#include "myisamdef.h"

#define IS_CHAR ((uint) 32768)		/* Bit if char (not offset) in tree */

/* Some definitions to keep in sync with myisampack.c */

#define HEAD_LENGTH	32              /* Length of fixed header */

#if INT_MAX > 32767

#define BITS_SAVED 32

#define MAX_QUICK_TABLE_BITS 9		/* Because we may shift in 24 bits */

#else

#define BITS_SAVED 16

#define MAX_QUICK_TABLE_BITS 6

#endif

#define get_bit(BU) ((BU)->bits ? \

		     (BU)->current_byte & ((mi_bit_type) 1 << --(BU)->bits) :\

		     (fill_buffer(BU), (BU)->bits= BITS_SAVED-1,\

		      (BU)->current_byte & ((mi_bit_type) 1 << (BITS_SAVED-1))))

#define skip_to_next_byte(BU) ((BU)->bits&=~7)

#define get_bits(BU,count) (((BU)->bits >= count) ? (((BU)->current_byte >> ((BU)->bits-=count)) & mask[count]) : fill_and_get_bits(BU,count))

#define decode_bytes_test_bit(bit) \

  if (low_byte & (1 << (7-bit))) \

    pos++; \

  if (*pos & IS_CHAR) \

  { bits-=(bit+1); break; } \

  pos+= *pos

/* Size in uint16 of a Huffman tree for byte compression of 256 byte values. */

#define OFFSET_TABLE_SIZE 512

static uint read_huff_table(MI_BIT_BUFF *bit_buff,MI_DECODE_TREE *decode_tree,

			    uint16 **decode_table,uchar **intervall_buff,

			    uint16 *tmp_buff);

static void make_quick_table(uint16 *to_table,uint16 *decode_table,

			     uint *next_free,uint value,uint bits,

			     uint max_bits);

static void fill_quick_table(uint16 *table,uint bits, uint max_bits,

			     uint value);

static uint copy_decode_table(uint16 *to_pos,uint offset,

			      uint16 *decode_table);

static uint find_longest_bitstream(uint16 *table, uint16 *end);

static void (*get_unpack_function(MI_COLUMNDEF *rec))(MI_COLUMNDEF *field,

						    MI_BIT_BUFF *buff,

						    uchar *to,

						    uchar *end);

static void uf_zerofill_skip_zero(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

				   uchar *to,uchar *end);

static void uf_skip_zero(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			  uchar *to,uchar *end);

static void uf_space_normal(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			    uchar *to,uchar *end);

static void uf_space_endspace_selected(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

				       uchar *to, uchar *end);

static void uf_endspace_selected(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

				 uchar *to,uchar *end);

static void uf_space_endspace(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			      uchar *to,uchar *end);

static void uf_endspace(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			uchar *to,uchar *end);

static void uf_space_prespace_selected(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

				       uchar *to, uchar *end);

static void uf_prespace_selected(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

				 uchar *to,uchar *end);

static void uf_space_prespace(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			      uchar *to,uchar *end);

static void uf_prespace(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			uchar *to,uchar *end);

static void uf_zerofill_normal(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			       uchar *to,uchar *end);

static void uf_constant(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			uchar *to,uchar *end);

static void uf_intervall(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			 uchar *to,uchar *end);

static void uf_zero(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

		    uchar *to,uchar *end);

static void uf_blob(MI_COLUMNDEF *rec, MI_BIT_BUFF *bit_buff,

		    uchar *to, uchar *end);

static void uf_varchar1(MI_COLUMNDEF *rec, MI_BIT_BUFF *bit_buff,

                        uchar *to, uchar *end);

static void uf_varchar2(MI_COLUMNDEF *rec, MI_BIT_BUFF *bit_buff,

                        uchar *to, uchar *end);

static void decode_bytes(MI_COLUMNDEF *rec,MI_BIT_BUFF *bit_buff,

			 uchar *to,uchar *end);

static uint decode_pos(MI_BIT_BUFF *bit_buff,MI_DECODE_TREE *decode_tree);

static void init_bit_buffer(MI_BIT_BUFF *bit_buff,uchar *buffer,uint length);

static uint fill_and_get_bits(MI_BIT_BUFF *bit_buff,uint count);

static void fill_buffer(MI_BIT_BUFF *bit_buff);

static uint max_bit(uint value);

#ifdef HAVE_MMAP

static uchar *_mi_mempack_get_block_info(MI_INFO *myisam, MI_BIT_BUFF *bit_buff,

                                         MI_BLOCK_INFO *info, uchar **rec_buff_p,

					 uchar *header);

#endif

static mi_bit_type mask[]=

{

   0x00000000,

   0x00000001, 0x00000003, 0x00000007, 0x0000000f,

   0x0000001f, 0x0000003f, 0x0000007f, 0x000000ff,

   0x000001ff, 0x000003ff, 0x000007ff, 0x00000fff,

   0x00001fff, 0x00003fff, 0x00007fff, 0x0000ffff,

#if BITS_SAVED > 16

   0x0001ffff, 0x0003ffff, 0x0007ffff, 0x000fffff,

   0x001fffff, 0x003fffff, 0x007fffff, 0x00ffffff,

   0x01ffffff, 0x03ffffff, 0x07ffffff, 0x0fffffff,

   0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff,

#endif

 };

	/* Read all packed info, allocate memory and fix field structs */

my_bool _mi_read_pack_info(MI_INFO *info, pbool fix_keys)

{

  File file;

  int diff_length;

  uint i,trees,huff_tree_bits,rec_reflength,length;

  uint16 *decode_table,*tmp_buff;

  ulong elements,intervall_length;

  uchar *disk_cache;

  uchar *intervall_buff;

  uchar header[HEAD_LENGTH];

  MYISAM_SHARE *share=info->s;

  MI_BIT_BUFF bit_buff;

  DBUG_ENTER("_mi_read_pack_info");

  if (myisam_quick_table_bits < 4)

    myisam_quick_table_bits=4;

  else if (myisam_quick_table_bits > MAX_QUICK_TABLE_BITS)

    myisam_quick_table_bits=MAX_QUICK_TABLE_BITS;

  file=info->dfile;

  my_errno=0;

  if (my_read(file,(uchar*) header,sizeof(header),MYF(MY_NABP)))

  {

    if (!my_errno)

      my_errno=HA_ERR_END_OF_FILE;

    goto err0;

  }

  /* Only the first three bytes of magic number are independent of version. */

  if (memcmp((uchar*) header, (uchar*) myisam_pack_file_magic, 3))

  {

    my_errno=HA_ERR_WRONG_IN_RECORD;

    goto err0;

  }

  share->pack.version= header[3]; /* fourth byte of magic number */

  share->pack.header_length=	uint4korr(header+4);

  share->min_pack_length=(uint) uint4korr(header+8);

  share->max_pack_length=(uint) uint4korr(header+12);

  elements=uint4korr(header+16);

  intervall_length=uint4korr(header+20);

  trees=uint2korr(header+24);

  share->pack.ref_length=header[26];

  rec_reflength=header[27];

  diff_length=(int) rec_reflength - (int) share->base.rec_reflength;

  if (fix_keys)

    share->rec_reflength=rec_reflength;

  share->base.min_block_length=share->min_pack_length+1;

  if (share->min_pack_length > 254)

    share->base.min_block_length+=2;

  DBUG_PRINT("info", ("fixed header length:   %u", HEAD_LENGTH));

  DBUG_PRINT("info", ("total header length:   %lu", share->pack.header_length));

  DBUG_PRINT("info", ("pack file version:     %u", share->pack.version));

  DBUG_PRINT("info", ("min pack length:       %lu", share->min_pack_length));

  DBUG_PRINT("info", ("max pack length:       %lu", share->max_pack_length));

  DBUG_PRINT("info", ("elements of all trees: %lu", elements));

  DBUG_PRINT("info", ("distinct values bytes: %lu", intervall_length));

  DBUG_PRINT("info", ("number of code trees:  %u", trees));

  DBUG_PRINT("info", ("bytes for record lgt:  %u", share->pack.ref_length));

  DBUG_PRINT("info", ("record pointer length: %u", rec_reflength));

  /*

    Memory segment #1:

    - Decode tree heads

    - Distinct column values

  */

  if (!(share->decode_trees=(MI_DECODE_TREE*)

	my_malloc((uint) (trees*sizeof(MI_DECODE_TREE)+

			  intervall_length*sizeof(uchar)),

		  MYF(MY_WME))))

    goto err0;

  intervall_buff=(uchar*) (share->decode_trees+trees);

  /*

    Memory segment #2:

    - Decode tables

    - Quick decode tables

    - Temporary decode table

    - Compressed data file header cache

    This segment will be reallocated after construction of the tables.

  */

  length=(uint) (elements*2+trees*(1 << myisam_quick_table_bits));

  if (!(share->decode_tables=(uint16*)

        my_malloc((length + OFFSET_TABLE_SIZE) * sizeof(uint16) +

                  (uint) (share->pack.header_length - sizeof(header)),

                  MYF(MY_WME | MY_ZEROFILL))))

    goto err1;

  tmp_buff=share->decode_tables+length;

  disk_cache= (uchar*) (tmp_buff+OFFSET_TABLE_SIZE);

  if (my_read(file,disk_cache,

	      (uint) (share->pack.header_length-sizeof(header)),

	      MYF(MY_NABP)))

    goto err2;

  huff_tree_bits=max_bit(trees ? trees-1 : 0);

  init_bit_buffer(&bit_buff, disk_cache,

		  (uint) (share->pack.header_length-sizeof(header)));

  /* Read new info for each field */

  for (i=0 ; i < share->base.fields ; i++)

  {

    share->rec[i].base_type=(enum en_fieldtype) get_bits(&bit_buff,5);

    share->rec[i].pack_type=(uint) get_bits(&bit_buff,6);

    share->rec[i].space_length_bits=get_bits(&bit_buff,5);

    share->rec[i].huff_tree=share->decode_trees+(uint) get_bits(&bit_buff,

								huff_tree_bits);

    share->rec[i].unpack=get_unpack_function(share->rec+i);

    DBUG_PRINT("info", ("col: %2u  type: %2u  pack: %u  slbits: %2u",

                        i, share->rec[i].base_type, share->rec[i].pack_type,

                        share->rec[i].space_length_bits));

  }

  skip_to_next_byte(&bit_buff);

  /*

    Construct the decoding tables from the file header. Keep track of

    the used memory.

  */

  decode_table=share->decode_tables;

  for (i=0 ; i < trees ; i++)

    if (read_huff_table(&bit_buff,share->decode_trees+i,&decode_table,

                        &intervall_buff,tmp_buff))

      goto err3;

  /* Reallocate the decoding tables to the used size. */

  decode_table=(uint16*)

    my_realloc((uchar*) share->decode_tables,

	       (uint) ((uchar*) decode_table - (uchar*) share->decode_tables),

	       MYF(MY_HOLD_ON_ERROR));

  /* Fix the table addresses in the tree heads. */

  {

    long diff=PTR_BYTE_DIFF(decode_table,share->decode_tables);

    share->decode_tables=decode_table;

    for (i=0 ; i < trees ; i++)

      share->decode_trees[i].table=ADD_TO_PTR(share->decode_trees[i].table,

                                              diff, uint16*);

  }

  /* Fix record-ref-length for keys */

  if (fix_keys)

  {

    for (i=0 ; i < share->base.keys ; i++)

    {

      MI_KEYDEF *keyinfo= &share->keyinfo[i];

      keyinfo->keylength+= (uint16) diff_length;

      keyinfo->minlength+= (uint16) diff_length;

      keyinfo->maxlength+= (uint16) diff_length;

      keyinfo->seg[keyinfo->keysegs].length= (uint16) rec_reflength;

    }

    if (share->ft2_keyinfo.seg)

    {

      MI_KEYDEF *ft2_keyinfo= &share->ft2_keyinfo;

      ft2_keyinfo->keylength+= (uint16) diff_length;

      ft2_keyinfo->minlength+= (uint16) diff_length;

      ft2_keyinfo->maxlength+= (uint16) diff_length;

    }

  }

  if (bit_buff.error || bit_buff.pos < bit_buff.end)

    goto err3;

  DBUG_RETURN(0);

err3:

  my_errno=HA_ERR_WRONG_IN_RECORD;

err2:

  my_free((uchar*) share->decode_tables,MYF(0));

err1:

  my_free((uchar*) share->decode_trees,MYF(0));

err0:

  DBUG_RETURN(1);

}

/*

  Read a huff-code-table from datafile.

  SYNOPSIS

    read_huff_table()

      bit_buff                  Bit buffer pointing at start of the

                                decoding table in the file header cache.

      decode_tree               Pointer to the decode tree head.

      decode_table      IN/OUT  Address of a pointer to the next free space.

      intervall_buff    IN/OUT  Address of a pointer to the next unused values.

      tmp_buff                  Buffer for temporary extraction of a full

                                decoding table as read from bit_buff.

  RETURN

    0           OK.

    1           Error.

*/

static uint read_huff_table(MI_BIT_BUFF *bit_buff, MI_DECODE_TREE *decode_tree,

			    uint16 **decode_table, uchar **intervall_buff,

			    uint16 *tmp_buff)

{

  uint min_chr,elements,char_bits,offset_bits,size,intervall_length,table_bits,

  next_free_offset;

  uint16 *ptr,*end;

  DBUG_ENTER("read_huff_table");

  if (!get_bits(bit_buff,1))

  {

    /* Byte value compression. */

    min_chr=get_bits(bit_buff,8);

    elements=get_bits(bit_buff,9);

    char_bits=get_bits(bit_buff,5);

    offset_bits=get_bits(bit_buff,5);

    intervall_length=0;

    ptr=tmp_buff;

    DBUG_PRINT("info", ("byte value compression"));

    DBUG_PRINT("info", ("minimum byte value:    %u", min_chr));

    DBUG_PRINT("info", ("number of tree nodes:  %u", elements));

    DBUG_PRINT("info", ("bits for values:       %u", char_bits));

    DBUG_PRINT("info", ("bits for tree offsets: %u", offset_bits));

    if (elements > 256)

    {

      DBUG_PRINT("error", ("ERROR: illegal number of tree elements: %u",

                           elements));

      DBUG_RETURN(1);

    }

  }

  else

  {

    /* Distinct column value compression. */

    min_chr=0;

    elements=get_bits(bit_buff,15);

    intervall_length=get_bits(bit_buff,16);

    char_bits=get_bits(bit_buff,5);

    offset_bits=get_bits(bit_buff,5);

    decode_tree->quick_table_bits=0;

    ptr= *decode_table;

    DBUG_PRINT("info", ("distinct column value compression"));

    DBUG_PRINT("info", ("number of tree nodes:  %u", elements));

    DBUG_PRINT("info", ("value buffer length:   %u", intervall_length));

    DBUG_PRINT("info", ("bits for value index:  %u", char_bits));

    DBUG_PRINT("info", ("bits for tree offsets: %u", offset_bits));

  }

  size=elements*2-2;

  DBUG_PRINT("info", ("tree size in uint16:   %u", size));

  DBUG_PRINT("info", ("tree size in bytes:    %u",

                      size * (uint) sizeof(uint16)));

  for (end=ptr+size ; ptr < end ; ptr++)

  {

    if (get_bit(bit_buff))

    {

      *ptr= (uint16) get_bits(bit_buff,offset_bits);

      if ((ptr + *ptr >= end) || !*ptr)

      {

        DBUG_PRINT("error", ("ERROR: illegal pointer in decode tree"));

        DBUG_RETURN(1);

      }

    }

    else

      *ptr= (uint16) (IS_CHAR + (get_bits(bit_buff,char_bits) + min_chr));

  }

  skip_to_next_byte(bit_buff);

  decode_tree->table= *decode_table;

  decode_tree->intervalls= *intervall_buff;

  if (! intervall_length)

  {

    /* Byte value compression. ptr started from tmp_buff. */

    /* Find longest Huffman code from begin to end of tree in bits. */

    table_bits= find_longest_bitstream(tmp_buff, ptr);

    if (table_bits >= OFFSET_TABLE_SIZE)

      DBUG_RETURN(1);

    if (table_bits > myisam_quick_table_bits)

      table_bits=myisam_quick_table_bits;

    DBUG_PRINT("info", ("table bits:            %u", table_bits));

    next_free_offset= (1 << table_bits);

    make_quick_table(*decode_table,tmp_buff,&next_free_offset,0,table_bits,

		     table_bits);

    (*decode_table)+= next_free_offset;

    decode_tree->quick_table_bits=table_bits;

  }

  else

  {

    /* Distinct column value compression. ptr started from *decode_table */

    (*decode_table)=end;

    /*

      get_bits() moves some bytes to a cache buffer in advance. May need

      to step back.

    */

    bit_buff->pos-= bit_buff->bits/8;

    /* Copy the distinct column values from the buffer. */

    memcpy(*intervall_buff,bit_buff->pos,(size_t) intervall_length);

    (*intervall_buff)+=intervall_length;

    bit_buff->pos+=intervall_length;

    bit_buff->bits=0;

  }

  DBUG_RETURN(0);

}

/*

  Make a quick_table for faster decoding.

  SYNOPSIS

    make_quick_table()

      to_table                  Target quick_table and remaining decode table.

      decode_table              Source Huffman (sub-)tree within tmp_buff.

      next_free_offset   IN/OUT Next free offset from to_table.

                                Starts behind quick_table on the top-level.

      value                     Huffman bits found so far.

      bits                      Remaining bits to be collected.

      max_bits                  Total number of bits to collect (table_bits).

  DESCRIPTION

    The quick table is an array of 16-bit values. There exists one value

    for each possible code representable by max_bits (table_bits) bits.

    In most cases table_bits is 9. So there are 512 16-bit values.

    If the high-order bit (16) is set (IS_CHAR) then the array slot for

    this value is a valid Huffman code for a resulting byte value.

    The low-order 8 bits (1..8) are the resulting byte value.

    Bits 9..14 are the length of the Huffman code for this byte value.

    This means so many bits from the input stream were needed to

    represent this byte value. The remaining bits belong to later

    Huffman codes. This also means that for every Huffman code shorter

    than table_bits there are multiple entires in the array, which

    differ just in the unused bits.

    If the high-order bit (16) is clear (0) then the remaining bits are

    the position of the remaining Huffman decode tree segment behind the

    quick table.

  RETURN

    void

*/

static void make_quick_table(uint16 *to_table, uint16 *decode_table,

			     uint *next_free_offset, uint value, uint bits,

			     uint max_bits)

{

  DBUG_ENTER("make_quick_table");

  /*

    When down the table to the requested maximum, copy the rest of the

    Huffman table.

  */

  if (!bits--)

  {

    /*

      Remaining left  Huffman tree segment starts behind quick table.

      Remaining right Huffman tree segment starts behind left segment.

    */

    to_table[value]= (uint16) *next_free_offset;

    /*

      Re-construct the remaining Huffman tree segment at

      next_free_offset in to_table.

    */

    *next_free_offset= copy_decode_table(to_table, *next_free_offset,

                                         decode_table);

    DBUG_VOID_RETURN;

  }

  /* Descent on the left side. Left side bits are clear (0). */

  if (!(*decode_table & IS_CHAR))

  {

    /* Not a leaf. Follow the pointer. */

    make_quick_table(to_table, decode_table + *decode_table,

                     next_free_offset, value, bits, max_bits);

  }

  else

  {

    /*

      A leaf. A Huffman code is complete. Fill the quick_table

      array for all possible bit strings starting with this Huffman

      code.

    */

    fill_quick_table(to_table + value, bits, max_bits, (uint) *decode_table);

  }

  /* Descent on the right side. Right side bits are set (1). */

  decode_table++;

  value|= (1 << bits);

  if (!(*decode_table & IS_CHAR))

  {

    /* Not a leaf. Follow the pointer. */

    make_quick_table(to_table, decode_table + *decode_table,

                     next_free_offset, value, bits, max_bits);

  }

  else

  {

    /*

      A leaf. A Huffman code is complete. Fill the quick_table

      array for all possible bit strings starting with this Huffman

      code.

    */

    fill_quick_table(to_table + value, bits, max_bits, (uint) *decode_table);

  }

  DBUG_VOID_RETURN;

}

/*

  Fill quick_table for all possible values starting with this Huffman code.

  SYNOPSIS

    fill_quick_table()

      table                     Target quick_table position.

      bits                      Unused bits from max_bits.

      max_bits                  Total number of bits to collect (table_bits).

      value                     The byte encoded by the found Huffman code.

  DESCRIPTION

    Fill the segment (all slots) of the quick_table array with the

    resulting value for the found Huffman code. There are as many slots

    as there are combinations representable by the unused bits.

    In most cases we use 9 table bits. Assume a 3-bit Huffman code. Then

    there are 6 unused bits. Hence we fill 2**6 = 64 slots with the

    value.

  RETURN

    void

*/

static void fill_quick_table(uint16 *table, uint bits, uint max_bits,

			     uint value)

{

  uint16 *end;

  DBUG_ENTER("fill_quick_table");

  /*

    Bits 1..8 of value represent the decoded byte value.

    Bits 9..14 become the length of the Huffman code for this byte value.

    Bit 16 flags a valid code (IS_CHAR).

  */

  value|= (max_bits - bits) << 8 | IS_CHAR;

  for (end= table + ((my_ptrdiff_t) 1 << bits); table < end; table++)

  {

    *table= (uint16) value;

  }

  DBUG_VOID_RETURN;

}

/*

  Reconstruct a decode subtree at the target position.

  SYNOPSIS

    copy_decode_table()

      to_pos                    Target quick_table and remaining decode table.

      offset                    Next free offset from to_pos.

      decode_table              Source Huffman subtree within tmp_buff.

  NOTE

    Pointers in the decode tree are relative to the pointers position.

  RETURN

    next free offset from to_pos.

*/

static uint copy_decode_table(uint16 *to_pos, uint offset,

			      uint16 *decode_table)

{

  uint prev_offset= offset;

  DBUG_ENTER("copy_decode_table");

  /* Descent on the left side. */

  if (!(*decode_table & IS_CHAR))

  {

    /* Set a pointer to the next target node. */

    to_pos[offset]=2;

    /* Copy the left hand subtree there. */

    offset=copy_decode_table(to_pos,offset+2,decode_table+ *decode_table);

  }

  else

  {

    /* Copy the byte value. */

    to_pos[offset]= *decode_table;

    /* Step behind this node. */

    offset+=2;

  }

  /* Descent on the right side. */

  decode_table++;

  if (!(*decode_table & IS_CHAR))

  {

    /* Set a pointer to the next free target node. */

    to_pos[prev_offset+1]=(uint16) (offset-prev_offset-1);

    /* Copy the right hand subtree to the entry of that node. */

    offset=copy_decode_table(to_pos,offset,decode_table+ *decode_table);

  }

  else

  {

    /* Copy the byte value. */

    to_pos[prev_offset+1]= *decode_table;

  }

  DBUG_RETURN(offset);

}

/*

  Find the length of the longest Huffman code in this table in bits.

  SYNOPSIS

    find_longest_bitstream()

      table                     Code (sub-)table start.

      end                       End of code table.

  IMPLEMENTATION

    Recursively follow the branch(es) of the code pair on every level of

    the tree until two byte values (and no branch) are found. Add one to

    each level when returning back from each recursion stage.

    'end' is used for error checking only. A clean tree terminates

    before reaching 'end'. Hence the exact value of 'end' is not too

    important. However having it higher than necessary could lead to

    misbehaviour should 'next' jump into the dirty area.

  RETURN

    length                  Length of longest Huffman code in bits.

    >= OFFSET_TABLE_SIZE    Error, broken tree. It does not end before 'end'.

*/

static uint find_longest_bitstream(uint16 *table, uint16 *end)

{

  uint length= 1;

  uint length2;

  if (!(*table & IS_CHAR))

  {

    uint16 *next= table + *table;

    if (next > end || next == table)

    {

      DBUG_PRINT("error", ("ERROR: illegal pointer in decode tree"));

      return OFFSET_TABLE_SIZE;

    }

    length= find_longest_bitstream(next, end) + 1;

  }

  table++;

  if (!(*table & IS_CHAR))

  {

    uint16 *next= table + *table;

    if (next > end || next == table)

    {

      DBUG_PRINT("error", ("ERROR: illegal pointer in decode tree"));

      return OFFSET_TABLE_SIZE;

    }

    length2= find_longest_bitstream(next, end) + 1;

    length=max(length,length2);

  }

  return length;

}

/*

  Read record from datafile.

  SYNOPSIS

    _mi_read_pack_record()

    info                        A pointer to MI_INFO.

    filepos                     File offset of the record.

    buf                 RETURN  The buffer to receive the record.

  RETURN

    0                                   on success

    HA_ERR_WRONG_IN_RECORD or -1        on error

*/

int _mi_read_pack_record(MI_INFO *info, my_off_t filepos, uchar *buf)

{

  MI_BLOCK_INFO block_info;

  File file;

  DBUG_ENTER("mi_read_pack_record");

  if (filepos == HA_OFFSET_ERROR)

    DBUG_RETURN(-1);			/* _search() didn't find record */

  file=info->dfile;

  if (_mi_pack_get_block_info(info, &info->bit_buff, &block_info,

                              &info->rec_buff, file, filepos))

    goto err;

  if (my_read(file,(uchar*) info->rec_buff + block_info.offset ,

	      block_info.rec_len - block_info.offset, MYF(MY_NABP)))

    goto panic;

  info->update|= HA_STATE_AKTIV;

  DBUG_RETURN(_mi_pack_rec_unpack(info, &info->bit_buff, buf,

                                  info->rec_buff, block_info.rec_len));

panic:

  my_errno=HA_ERR_WRONG_IN_RECORD;

err:

  DBUG_RETURN(-1);

}

int _mi_pack_rec_unpack(register MI_INFO *info, MI_BIT_BUFF *bit_buff,

                        register uchar *to, uchar *from, ulong reclength)

{

  uchar *end_field;

  register MI_COLUMNDEF *end;

  MI_COLUMNDEF *current_field;

  MYISAM_SHARE *share=info->s;

  DBUG_ENTER("_mi_pack_rec_unpack");

  init_bit_buffer(bit_buff, (uchar*) from, reclength);

  for (current_field=share->rec, end=current_field+share->base.fields ;

       current_field < end ;

       current_field++,to=end_field)

  {

    end_field=to+current_field->length;

    (*current_field->unpack)(current_field, bit_buff, (uchar*) to,

			     (uchar*) end_field);

  }

  if (!bit_buff->error &&

      bit_buff->pos - bit_buff->bits / 8 == bit_buff->end)

    DBUG_RETURN(0);

  info->update&= ~HA_STATE_AKTIV;

  DBUG_RETURN(my_errno=HA_ERR_WRONG_IN_RECORD);

} /* _mi_pack_rec_unpack */

	/* Return function to unpack field */

static void (*get_unpack_function(MI_COLUMNDEF *rec))

(MI_COLUMNDEF *, MI_BIT_BUFF *, uchar *, uchar *)

{

  switch (rec->base_type) {

  case FIELD_SKIP_ZERO:

    if (rec->pack_type & PACK_TYPE_ZERO_FILL)

      return &uf_zerofill_skip_zero;

    return &uf_skip_zero;

  case FIELD_NORMAL:

    if (rec->pack_type & PACK_TYPE_SPACE_FIELDS)