SQLite

** Boston, MA  02111-1307, USA.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** $Id: btree.c,v 1.3 2001/04/29 23:32:56 drh Exp $
*/
#include "sqliteInt.h"
#include "pager.h"
#include "btree.h"
#include <assert.h>

typedef unsigned int u32;


/*
** The first page contains the following additional information:
**
**      MAGIC-1
**      MAGIC-2
**      First free block
*/
#define EXTRA_PAGE_1_CELLS  3
#define MAGIC_1  0x7264dc61
#define MAGIC_2  0x54e55d9e

/*
** Each database page has a header as follows:
**
**      page1_header          Extra numbers found on page 1 only.
**      leftmost_pgno         Page number of the leftmost child
**      first_cell            Index into MemPage.aPage of first cell
**      first_free            Index of first free block
**
** MemPage.pStart always points to the leftmost_pgno.  First_free is
** 0 if there is no free space on this page.  Otherwise it points to
** an area like this:
**
**      nByte                 Number of free bytes in this block
**      next_free             Next free block or 0 if this is the end
*/

/*
** The maximum number of database entries that can be held in a single
** page of the database.  Each entry has a 16-byte header consisting of
** 4 unsigned 32-bit numbers, as follows:
**
**       nKey       Number of byte in the key
**       nData      Number of byte in the data
**       pgno       Page number of the right child block 
**       next       index in MemPage.aPage[] of the next entry in sorted order
**
** The key and data follow this header.  The key and data are packed together
** and the total rounded up to the next multiple of 4 bytes.  There must
** be at least 4 bytes in the key/data packet, so each entry consumes at
** least 20 bytes of space on the page.
*/
#define MX_CELL ((SQLITE_PAGE_SIZE-12)/20)







/*
** The maximum amount of data (in bytes) that can be stored locally for a
** database entry.  If the entry contains more data than this, the
** extra goes onto overflow pages.
*/
#define MX_LOCAL_PAYLOAD ((SQLITE_PAGE_SIZE-20-4*24)/4)

  unsigned char validUp;                    /* True if MemPage.up is valid */
  unsigned char validLeft;                  /* True if MemPage.left is valid */
  unsigned char validRight;                 /* True if MemPage.right is valid */
  Pgno up;                     /* The parent page.  0 means this is the root */
  Pgno left;                   /* Left sibling page.  0==none */
  Pgno right;                  /* Right sibling page.  0==none */
  int idxStart;                /* Index in aPage[] of real data */
  int nFree;                   /* Number of free elements of aPage[] */
  int nCell;                   /* Number of entries on this page */
  u32 *aCell[MX_CELL];         /* All entires in sorted order */



}
typedef struct MemPage;

/*
** The in-memory image of a disk page has the auxiliary information appended
** to the end.  EXTRA_SIZE is the number of bytes of space needed to hold
** that extra information.

  BtCursor *pPrev, *pNext;      /* Linked list of all cursors */
  int valid;                    /* True if the cursor points to something */
  int nLevel;                   /* Number of levels of indexing used */
  BtIdxpt *pLevel;              /* Pointer to aLevel[nLevel] */
  BtIdxpt aLevel[MX_LEVEL];     /* The index levels */
};






















/*
** Mark a section of the memory block as in-use.
*/
static void useSpace(MemPage *pPage, int start, int size){
  int i;
  FreeBlk *p;

      *p = pPage->aFree[pPage->nFree-1];
      pPage->nFree--;
    }
  }else if( p->idx+p->size==start+size ){
    /* Space at the end of the block */
    p->size -= size;
  }else{
    /* Space in the middle of the freeblock. */
    FreeBlk *pNew;
    assert( p->nFreeSlot < MX_FREE );
    pNew->idx = start+size;
    pNew->size = p->idx+p->size - pNew->idx;
    p->size = start - p->idx;
  }
  pPage->nFreeSlot -= size;
}

/*
** Return a section of the MemPage.aPage[] to the freelist.
*/
static void freeSpace(MemPage *pPage, int start, int size){
  int end = start+size;
  int i;
  FreeBlk *pMatch = 0;
  FreeBlk *
  for(i=0; i<pPage->nFreeSlot; i++){
    FreeBlk *p = &pPage->aFree[i];
    if( p->idx==end+1 ){
      if( pMatch ){
        
      }else{
        p->idx = start;
        p->size += size;
        pMatch = p;
      }
    }
    if( p->idx+p->size+1==start ){
      p->size += size;
      break;
    }
  }
}

/*
** Defragment the freespace
*/
static void defragmentSpace(MemPage *pPage){
}