/*

** 2007 October 14

**

** The author disclaims copyright to this source code.  In place of

** a legal notice, here is a blessing:

**

**    May you do good and not evil.

**    May you find forgiveness for yourself and forgive others.

**    May you share freely, never taking more than you give.

**

*************************************************************************

** This file contains the C functions that implement a memory

** allocation subsystem for use by SQLite. 

**

** This version of the memory allocation subsystem omits all

** use of malloc(). The SQLite user supplies a block of memory

** before calling sqlite3_initialize() from which allocations

** are made and returned by the xMalloc() and xRealloc() 

** implementations. Once sqlite3_initialize() has been called,

** the amount of memory available to SQLite is fixed and cannot

** be changed.

**

** This version of the memory allocation subsystem is included

** in the build only if SQLITE_ENABLE_MEMSYS5 is defined.

**

** $Id: mem5.c,v 1.14 2008/09/02 17:52:52 danielk1977 Exp $

*/

#include "sqliteInt.h"

/*

** This version of the memory allocator is used only when 

** SQLITE_POW2_MEMORY_SIZE is defined.

*/

#ifdef SQLITE_ENABLE_MEMSYS5

/*

** Log2 of the minimum size of an allocation.  For example, if

** 4 then all allocations will be rounded up to at least 16 bytes.

** If 5 then all allocations will be rounded up to at least 32 bytes.

*/

#ifndef SQLITE_POW2_LOGMIN

# define SQLITE_POW2_LOGMIN 6

#endif

/*

** Log2 of the maximum size of an allocation.

*/

#ifndef SQLITE_POW2_LOGMAX

# define SQLITE_POW2_LOGMAX 20

#endif

#define POW2_MAX (((unsigned int)1)<<SQLITE_POW2_LOGMAX)

/*

** Number of distinct allocation sizes.

*/

#define NSIZE (SQLITE_POW2_LOGMAX - SQLITE_POW2_LOGMIN + 1)

/*

** A minimum allocation is an instance of the following structure.

** Larger allocations are an array of these structures where the

** size of the array is a power of 2.

*/

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.nAtom). Since

** mem5.nAtom is always at least 8, this is not really a practical

** limitation.

*/

#define LOGMAX 30

/*

** Masks used for mem5.aCtrl[] elements.

*/

#define CTRL_LOGSIZE  0x1f    /* Log2 Size of this block relative to POW2_MIN */

#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 nAtom;       /* Smallest possible allocation in bytes */

  int nBlock;      /* Number of nAtom sized blocks in zPool */

  u8 *zPool;

  /*

  ** 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 of various sizes.

  */

  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 = { 19804167 };

#define mem5 GLOBAL(struct Mem5Global, mem5)

#define MEM5LINK(idx) ((Mem5Link *)(&mem5.zPool[(idx)*mem5.nAtom]))

/*

** 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;

  assert( i>=0 && i<mem5.nBlock );

  assert( iLogsize>=0 && iLogsize<=LOGMAX );

  assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );

  next = MEM5LINK(i)->next;

  prev = MEM5LINK(i)->prev;

  if( prev<0 ){

    mem5.aiFreelist[iLogsize] = next;

  }else{

    MEM5LINK(prev)->next = next;

  }

  if( next>=0 ){

    MEM5LINK(next)->prev = prev;

  }

}

/*

** Link the chunk at mem5.aPool[i] so that is on the iLogsize

** free list.

*/

static void memsys5Link(int i, int iLogsize){

  int x;

  assert( sqlite3_mutex_held(mem5.mutex) );

  assert( i>=0 && i<mem5.nBlock );

  assert( iLogsize>=0 && iLogsize<=LOGMAX );

  assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );

  x = MEM5LINK(i)->next = mem5.aiFreelist[iLogsize];

  MEM5LINK(i)->prev = -1;

  if( x>=0 ){

    assert( x<mem5.nBlock );

    MEM5LINK(x)->prev = i;

  }

  mem5.aiFreelist[iLogsize] = i;

}

/*

** If the STATIC_MEM mutex is not already held, obtain it now. The mutex

** will already be held (obtained by code in malloc.c) if

** sqlite3GlobalConfig.bMemStat is true.

*/

static void memsys5Enter(void){

  if( sqlite3GlobalConfig.bMemstat==0 && mem5.mutex==0 ){

    mem5.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);

  }

  sqlite3_mutex_enter(mem5.mutex);

}

static void memsys5Leave(void){

  sqlite3_mutex_leave(mem5.mutex);

}

/*

** 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.nAtom;

    assert( i>=0 && i<mem5.nBlock );

    iSize = mem5.nAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));

  }

  return iSize;

}

/*

** Find the first entry on the freelist iLogsize.  Unlink that

** entry and return its index. 

*/

static int memsys5UnlinkFirst(int iLogsize){

  int i;

  int iFirst;

  assert( iLogsize>=0 && iLogsize<=LOGMAX );

  i = iFirst = mem5.aiFreelist[iLogsize];

  assert( iFirst>=0 );

  while( i>0 ){

    if( i<iFirst ) iFirst = i;

    i = MEM5LINK(i)->next;

  }

  memsys5Unlink(iFirst, iLogsize);

  return iFirst;

}

/*

** Return a block of memory of at least nBytes in size.

** Return NULL if unable.

*/

static void *memsys5MallocUnsafe(int nByte){

  int i;           /* Index of a mem5.aPool[] slot */

  int iBin;        /* Index into mem5.aiFreelist[] */

  int iFullSz;     /* Size of allocation rounded up to power of 2 */

  int iLogsize;    /* Log2 of iFullSz/POW2_MIN */

  /* Keep track of the maximum allocation request.  Even unfulfilled

  ** requests are counted */

  if( nByte>mem5.maxRequest ){

    mem5.maxRequest = nByte;

  }

  /* Round nByte up to the next valid power of two */

  if( nByte>POW2_MAX ) return 0;

  for(iFullSz=mem5.nAtom, 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;

  i = memsys5UnlinkFirst(iBin);

  while( iBin>iLogsize ){

    int newSize;

    iBin--;

    newSize = 1 << iBin;

    mem5.aCtrl[i+newSize] = CTRL_FREE | iBin;

    memsys5Link(i+newSize, iBin);

  }

  mem5.aCtrl[i] = iLogsize;

  /* Update allocator performance statistics. */

  mem5.nAlloc++;

  mem5.totalAlloc += iFullSz;

  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.nAtom];

}

/*

** 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.nAtom byte blocks pointed to by mem5.zPool.

  */

  iBlock = ((u8 *)pOld-mem5.zPool)/mem5.nAtom;

  /* Check that the pointer pOld points to a valid, non-free block. */

  assert( iBlock>=0 && iBlock<mem5.nBlock );

  assert( ((u8 *)pOld-mem5.zPool)%mem5.nAtom==0 );

  assert( (mem5.aCtrl[iBlock] & CTRL_FREE)==0 );

  iLogsize = mem5.aCtrl[iBlock] & CTRL_LOGSIZE;

  size = 1<<iLogsize;

  assert( iBlock+size-1<mem5.nBlock );

  mem5.aCtrl[iBlock] |= CTRL_FREE;

  mem5.aCtrl[iBlock+size-1] |= CTRL_FREE;

  assert( mem5.currentCount>0 );

  assert( mem5.currentOut>=0 );

  mem5.currentCount--;

  mem5.currentOut -= size*mem5.nAtom;

  assert( mem5.currentOut>0 || mem5.currentCount==0 );

  assert( mem5.currentCount>0 || mem5.currentOut==0 );

  mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;

  while( iLogsize<LOGMAX ){

    int iBuddy;

    if( (iBlock>>iLogsize) & 1 ){

      iBuddy = iBlock - size;

    }else{

      iBuddy = iBlock + size;

    }

    assert( iBuddy>=0 );

    if( (iBuddy+(1<<iLogsize))>mem5.nBlock ) break;

    if( mem5.aCtrl[iBuddy]!=(CTRL_FREE | iLogsize) ) break;

    memsys5Unlink(iBuddy, iLogsize);

    iLogsize++;

    if( iBuddy<iBlock ){

      mem5.aCtrl[iBuddy] = CTRL_FREE | iLogsize;

      mem5.aCtrl[iBlock] = 0;

      iBlock = iBuddy;

    }else{

      mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;

      mem5.aCtrl[iBuddy] = 0;

    }

    size *= 2;

  }

  memsys5Link(iBlock, iLogsize);

}

/*

** Allocate nBytes of memory

*/

static void *memsys5Malloc(int nBytes){

  sqlite3_int64 *p = 0;

  if( nBytes>0 ){

    memsys5Enter();

    p = memsys5MallocUnsafe(nBytes);

    memsys5Leave();

  }

  return (void*)p; 

}

/*

** Free memory.

*/

static void memsys5Free(void *pPrior){

  if( pPrior==0 ){

assert(0);

    return;

  }

  memsys5Enter();

  memsys5FreeUnsafe(pPrior);

  memsys5Leave();  

}

/*

** Change the size of an existing memory allocation

*/

static void *memsys5Realloc(void *pPrior, int nBytes){

  int nOld;

  void *p;

  if( pPrior==0 ){

    return memsys5Malloc(nBytes);

  }

  if( nBytes<=0 ){

    memsys5Free(pPrior);

    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.

*/

static int memsys5Roundup(int n){

  int iFullSz;

  for(iFullSz=mem5.nAtom; iFullSz<n; iFullSz *= 2);

  return iFullSz;

}

static int memsys5Log(int iValue){

  int iLog;

  for(iLog=0; (1<<iLog)<iValue; iLog++);

  return iLog;

}

/*

** Initialize this module.

*/

static int memsys5Init(void *NotUsed){

  int ii;

  int nByte = sqlite3GlobalConfig.nHeap;

  u8 *zByte = (u8 *)sqlite3GlobalConfig.pHeap;

  int nMinLog;                 /* Log of minimum allocation size in bytes*/

  int iOffset;

  if( !zByte ){

    return SQLITE_ERROR;

  }

  nMinLog = memsys5Log(sqlite3GlobalConfig.mnReq);

  mem5.nAtom = (1<<nMinLog);

  while( sizeof(Mem5Link)>mem5.nAtom ){

    mem5.nAtom = mem5.nAtom << 1;

  }

  mem5.nBlock = (nByte / (mem5.nAtom+sizeof(u8)));

  mem5.zPool = zByte;

  mem5.aCtrl = (u8 *)&mem5.zPool[mem5.nBlock*mem5.nAtom];

  for(ii=0; ii<=LOGMAX; ii++){

    mem5.aiFreelist[ii] = -1;

  }

  iOffset = 0;

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

    int nAlloc = (1<<ii);

    if( (iOffset+nAlloc)<=mem5.nBlock ){

      mem5.aCtrl[iOffset] = ii | CTRL_FREE;

      memsys5Link(iOffset, ii);

      iOffset += nAlloc;

    }

    assert((iOffset+nAlloc)>mem5.nBlock);

  }

  return SQLITE_OK;

}

/*

** Deinitialize this module.

*/

static void memsys5Shutdown(void *NotUsed){

  return;

}

/*

** Open the file indicated and write a log of all unfreed memory 

** allocations into that log.

*/

void sqlite3Memsys5Dump(const char *zFilename){

#ifdef SQLITE_DEBUG

  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.nAtom);

  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.nAtom << 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){

  static const sqlite3_mem_methods memsys5Methods = {

     memsys5Malloc,

     memsys5Free,

     memsys5Realloc,

     memsys5Size,

     memsys5Roundup,

     memsys5Init,

     memsys5Shutdown,

     0

  };

  return &memsys5Methods;

}

#endif /* SQLITE_ENABLE_MEMSYS5 */