SQLite

    return 0;
  }
  if( nBytes>=0x7fffff00 ){
    /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
    return 0;
  }
  nOld = sqlite3MallocSize(pOld);



  nNew = sqlite3GlobalConfig.m.xRoundup(nBytes);
  if( nOld==nNew ){
    pNew = pOld;
  }else if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, nBytes);
    if( sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED)+nNew-nOld >= 
          mem0.alarmThreshold ){
      sqlite3MallocAlarm(nNew-nOld);
    }
    pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
    if( pNew==0 && mem0.alarmCallback ){
      sqlite3MallocAlarm(nBytes);
      pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
    }
    if( pNew ){
      nNew = sqlite3MallocSize(pNew);
      sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, nNew-nOld);
    }

    sqlite3_mutex_leave(mem0.mutex);
  }else{
    pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
  }
  return pNew;
}

/*
** The public interface to sqlite3Realloc.  Make sure that the memory
** subsystem is initialized prior to invoking sqliteRealloc.

** This version of the memory allocation subsystem is included
** in the build only if SQLITE_ENABLE_MEMSYS5 is defined.
**
** This memory allocator uses the following algorithm:
**
**   1.  All memory allocations sizes are rounded up to a power of 2.
**
**   2.  If two adjacent free blocks are the halves of a larger block,
**       then the two blocks are coalesed into the single larger block.
**
**   3.  New memory is allocated from the first available free block.
**
** This algorithm is described in: J. M. Robson. "Bounds for Some Functions
** Concerning Dynamic Storage Allocation". Journal of the Association for
** Computing Machinery, Volume 21, Number 8, July 1974, pages 491-499.
** 

typedef struct Mem5Link Mem5Link;
struct Mem5Link {
  int next;       /* Index of next free chunk */
  int prev;       /* Index of previous free chunk */
};

/*
** Maximum size of any allocation is ((1<<LOGMAX)*mem5.szAtom). Since
** mem5.szAtom is always at least 8 and 32-bit integers are used,
** it is not actually possible to reach this limit.
*/
#define LOGMAX 30

/*
** Masks used for mem5.aCtrl[] elements.
*/
#define CTRL_LOGSIZE  0x1f    /* Log2 Size of this block */
#define CTRL_FREE     0x20    /* True if not checked out */

/*
** All of the static variables used by this module are collected
** into a single structure named "mem5".  This is to keep the
** static variables organized and to reduce namespace pollution
** when this module is combined with other in the amalgamation.
*/
static SQLITE_WSD struct Mem5Global {
  /*
  ** Memory available for allocation
  */
  int szAtom;      /* Smallest possible allocation in bytes */
  int nBlock;      /* Number of szAtom sized blocks in zPool */
  u8 *zPool;       /* Memory available to be allocated */
  
  /*
  ** Mutex to control access to the memory allocation subsystem.
  */
  sqlite3_mutex *mutex;

  /*
  ** Performance statistics
  */
  u64 nAlloc;         /* Total number of calls to malloc */
  u64 totalAlloc;     /* Total of all malloc calls - includes internal frag */
  u64 totalExcess;    /* Total internal fragmentation */
  u32 currentOut;     /* Current checkout, including internal fragmentation */
  u32 currentCount;   /* Current number of distinct checkouts */
  u32 maxOut;         /* Maximum instantaneous currentOut */
  u32 maxCount;       /* Maximum instantaneous currentCount */
  u32 maxRequest;     /* Largest allocation (exclusive of internal frag) */
  
  /*
  ** Lists of free blocks.  aiFreelist[0] is a list of free blocks of
  ** size mem5.szAtom.  aiFreelist[1] holds blocks of size szAtom*2.
  ** and so forth.
  */
  int aiFreelist[LOGMAX+1];

  /*
  ** Space for tracking which blocks are checked out and the size
  ** of each block.  One byte per block.
  */
  u8 *aCtrl;

} mem5 = { 0 };

/*
** Access the static variable through a macro for SQLITE_OMIT_WSD
*/
#define mem5 GLOBAL(struct Mem5Global, mem5)

/*
** Assuming mem5.zPool is divided up into an array of Mem5Link
** structures, return a pointer to the idx-th such lik.
*/
#define MEM5LINK(idx) ((Mem5Link *)(&mem5.zPool[(idx)*mem5.szAtom]))

/*
** Unlink the chunk at mem5.aPool[i] from list it is currently
** on.  It should be found on mem5.aiFreelist[iLogsize].
*/
static void memsys5Unlink(int i, int iLogsize){
  int next, prev;

** Return the size of an outstanding allocation, in bytes.  The
** size returned omits the 8-byte header overhead.  This only
** works for chunks that are currently checked out.
*/
static int memsys5Size(void *p){
  int iSize = 0;
  if( p ){
    int i = ((u8 *)p-mem5.zPool)/mem5.szAtom;
    assert( i>=0 && i<mem5.nBlock );
    iSize = mem5.szAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));
  }
  return iSize;
}

/*
** Find the first entry on the freelist iLogsize.  Unlink that
** entry and return its index. 

  /* Keep track of the maximum allocation request.  Even unfulfilled
  ** requests are counted */
  if( (u32)nByte>mem5.maxRequest ){
    mem5.maxRequest = nByte;
  }

  /* Abort if the requested allocation size is larger than the largest
  ** power of two that we can represent using 32-bit signed integers.
  */
  if( nByte > 0x40000000 ){
    return 0;
  }

  /* Round nByte up to the next valid power of two */
  for(iFullSz=mem5.szAtom, iLogsize=0; iFullSz<nByte; iFullSz *= 2, iLogsize++){}

  /* Make sure mem5.aiFreelist[iLogsize] contains at least one free
  ** block.  If not, then split a block of the next larger power of
  ** two in order to create a new free block of size iLogsize.
  */
  for(iBin=iLogsize; mem5.aiFreelist[iBin]<0 && iBin<=LOGMAX; iBin++){}
  if( iBin>LOGMAX ) return 0;

  mem5.totalExcess += iFullSz - nByte;
  mem5.currentCount++;
  mem5.currentOut += iFullSz;
  if( mem5.maxCount<mem5.currentCount ) mem5.maxCount = mem5.currentCount;
  if( mem5.maxOut<mem5.currentOut ) mem5.maxOut = mem5.currentOut;

  /* Return a pointer to the allocated memory. */
  return (void*)&mem5.zPool[i*mem5.szAtom];
}

/*
** Free an outstanding memory allocation.
*/
static void memsys5FreeUnsafe(void *pOld){
  u32 size, iLogsize;
  int iBlock;

  /* Set iBlock to the index of the block pointed to by pOld in 
  ** the array of mem5.szAtom byte blocks pointed to by mem5.zPool.
  */
  iBlock = ((u8 *)pOld-mem5.zPool)/mem5.szAtom;

  /* Check that the pointer pOld points to a valid, non-free block. */
  assert( iBlock>=0 && iBlock<mem5.nBlock );
  assert( ((u8 *)pOld-mem5.zPool)%mem5.szAtom==0 );
  assert( (mem5.aCtrl[iBlock] & CTRL_FREE)==0 );

  iLogsize = mem5.aCtrl[iBlock] & CTRL_LOGSIZE;
  size = 1<<iLogsize;
  assert( iBlock+size-1<(u32)mem5.nBlock );

  mem5.aCtrl[iBlock] |= CTRL_FREE;
  mem5.aCtrl[iBlock+size-1] |= CTRL_FREE;
  assert( mem5.currentCount>0 );
  assert( mem5.currentOut>=(size*mem5.szAtom) );
  mem5.currentCount--;
  mem5.currentOut -= size*mem5.szAtom;
  assert( mem5.currentOut>0 || mem5.currentCount==0 );
  assert( mem5.currentCount>0 || mem5.currentOut==0 );

  mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
  while( ALWAYS(iLogsize<LOGMAX) ){
    int iBuddy;
    if( (iBlock>>iLogsize) & 1 ){
      iBuddy = iBlock - size;
    }else{
      iBuddy = iBlock + size;
    }
    assert( iBuddy>=0 );

  memsys5Leave();  
}

/*
** Change the size of an existing memory allocation.
**
** The outer layer memory allocator prevents this routine from
** being called with pPrior==0.  
**
** nBytes is always a value obtained from a prior call to
** memsys5Round().  Hence nBytes is always a non-negative power
** of two.  If nBytes==0 that means that an oversize allocation
** (an allocation larger than 0x40000000) was requested and this
** routine should return 0 without freeing pPrior.
*/
static void *memsys5Realloc(void *pPrior, int nBytes){
  int nOld;
  void *p;
  assert( pPrior!=0 );
  assert( (nBytes&(nBytes-1))==0 );
  assert( nBytes>=0 );
  if( nBytes==0 ){

    return 0;
  }
  nOld = memsys5Size(pPrior);
  if( nBytes<=nOld ){
    return pPrior;
  }
  memsys5Enter();
  p = memsys5MallocUnsafe(nBytes);
  if( p ){
    memcpy(p, pPrior, nOld);
    memsys5FreeUnsafe(pPrior);
  }
  memsys5Leave();
  return p;
}

/*
** Round up a request size to the next valid allocation size.  If
** the allocation is too large to be handled by this allocation system,
** return 0.
**
** All allocations must be a power of two and must be expressed by a
** 32-bit signed integer.  Hence the largest allocation is 0x40000000
** or 1073741824 bytes.
*/
static int memsys5Roundup(int n){
  int iFullSz;
  if( n > 0x40000000 ) return 0;
  for(iFullSz=mem5.szAtom; iFullSz<n; iFullSz *= 2);
  return iFullSz;
}

/*
** Return the ceiling of the logarithm base 2 of iValue.
**
** Examples:   memsys5Log(1) -> 0
**             memsys5Log(2) -> 1
**             memsys5Log(4) -> 2
**             memsys5Log(5) -> 3
**             memsys5Log(8) -> 3
**             memsys5Log(9) -> 4
*/
static int memsys5Log(int iValue){
  int iLog;
  for(iLog=0; (1<<iLog)<iValue; iLog++);
  return iLog;
}

/*
** Initialize the memory allocator.
*/
static int memsys5Init(void *NotUsed){
  int ii;            /* Loop counter */
  int nByte;         /* Number of bytes of memory available to this allocator */
  u8 *zByte;         /* Memory usable by this allocator */
  int nMinLog;       /* Log base 2 of minimum allocation size in bytes */
  int iOffset;       /* An offset into mem5.aCtrl[] */

  UNUSED_PARAMETER(NotUsed);

  /* The size of a Mem5Link object must be a power of two.  Verify that
  ** this is case.
  */
  assert( (sizeof(Mem5Link)&(sizeof(Mem5Link)-1))==0 );

  nByte = sqlite3GlobalConfig.nHeap;
  zByte = (u8*)sqlite3GlobalConfig.pHeap;
  assert( zByte!=0 );  /* sqlite3_config() does not allow otherwise */

  nMinLog = memsys5Log(sqlite3GlobalConfig.mnReq);
  mem5.szAtom = (1<<nMinLog);
  while( (int)sizeof(Mem5Link)>mem5.szAtom ){
    mem5.szAtom = mem5.szAtom << 1;
  }

  mem5.nBlock = (nByte / (mem5.szAtom+sizeof(u8)));
  mem5.zPool = zByte;
  mem5.aCtrl = (u8 *)&mem5.zPool[mem5.nBlock*mem5.szAtom];

  for(ii=0; ii<=LOGMAX; ii++){
    mem5.aiFreelist[ii] = -1;
  }

  iOffset = 0;
  for(ii=LOGMAX; ii>=0; ii--){

*/
static void memsys5Shutdown(void *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  mem5.mutex = 0;
  return;
}

#ifdef SQLITE_TEST
/*
** Open the file indicated and write a log of all unfreed memory 
** allocations into that log.
*/
void sqlite3Memsys5Dump(const char *zFilename){

  FILE *out;
  int i, j, n;
  int nMinLog;

  if( zFilename==0 || zFilename[0]==0 ){
    out = stdout;
  }else{
    out = fopen(zFilename, "w");
    if( out==0 ){
      fprintf(stderr, "** Unable to output memory debug output log: %s **\n",
                      zFilename);
      return;
    }
  }
  memsys5Enter();
  nMinLog = memsys5Log(mem5.szAtom);
  for(i=0; i<=LOGMAX && i+nMinLog<32; i++){
    for(n=0, j=mem5.aiFreelist[i]; j>=0; j = MEM5LINK(j)->next, n++){}
    fprintf(out, "freelist items of size %d: %d\n", mem5.szAtom << i, n);
  }
  fprintf(out, "mem5.nAlloc       = %llu\n", mem5.nAlloc);
  fprintf(out, "mem5.totalAlloc   = %llu\n", mem5.totalAlloc);
  fprintf(out, "mem5.totalExcess  = %llu\n", mem5.totalExcess);
  fprintf(out, "mem5.currentOut   = %u\n", mem5.currentOut);
  fprintf(out, "mem5.currentCount = %u\n", mem5.currentCount);
  fprintf(out, "mem5.maxOut       = %u\n", mem5.maxOut);
  fprintf(out, "mem5.maxCount     = %u\n", mem5.maxCount);
  fprintf(out, "mem5.maxRequest   = %u\n", mem5.maxRequest);
  memsys5Leave();
  if( out==stdout ){
    fflush(stdout);
  }else{
    fclose(out);
  }



}
#endif

/*
** This routine is the only routine in this file with external 
** linkage. It returns a pointer to a static sqlite3_mem_methods
** struct populated with the memsys5 methods.
*/
const sqlite3_mem_methods *sqlite3MemGetMemsys5(void){