SQLite

#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* Designate a buffer for heap memory space */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      sqlite3GlobalConfig.mnReq = va_arg(ap, int);

      if( sqlite3GlobalConfig.mnReq<1 ){
        sqlite3GlobalConfig.mnReq = 1;
      }else if( sqlite3GlobalConfig.mnReq>(1<<12) ){
        /* cap min request size at 2^12 */
        sqlite3GlobalConfig.mnReq = (1<<12);
      }

      if( sqlite3GlobalConfig.pHeap==0 ){
        /* If the heap pointer is NULL, then restore the malloc implementation
        ** back to NULL pointers too.  This will cause the malloc to go
        ** back to its default implementation when sqlite3_initialize() is
        ** run.
        */

**             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++);
  for(iLog=0; (iLog<((sizeof(int)*8)-2)) && (1<<iLog)<iValue; iLog++);
  return iLog;
}

/*
** Initialize the memory allocator.
**
** This routine is not threadsafe.  The caller must be holding a mutex

  */
  assert( (sizeof(Mem5Link)&(sizeof(Mem5Link)-1))==0 );

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

  /* boundaries on sqlite3GlobalConfig.mnReq are enforced in sqlite3_config() */
  nMinLog = sqlite3GlobalConfig.mnReq;
  assert( nMinLog>0 && nMinLog<=(1<<12) );
  nMinLog = memsys5Log(sqlite3GlobalConfig.mnReq);
  nMinLog = memsys5Log(nMinLog);
  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;

** ^If the first pointer (the memory pointer) is NULL, then SQLite reverts
** to using its default memory allocator (the system malloc() implementation),
** undoing any prior invocation of [SQLITE_CONFIG_MALLOC].  ^If the
** memory pointer is not NULL and either [SQLITE_ENABLE_MEMSYS3] or
** [SQLITE_ENABLE_MEMSYS5] are defined, then the alternative memory
** allocator is engaged to handle all of SQLites memory allocation needs.
** The first pointer (the memory pointer) must be aligned to an 8-byte
** boundary or subsequent behavior of SQLite will be undefined.</dd>
** boundary or subsequent behavior of SQLite will be undefined.
** The minimum allocation size is capped at 2^12. Reasonable values
** for the minimum allocation size are 2^5 through 2^8.</dd>
**
** <dt>SQLITE_CONFIG_MUTEX</dt>
** <dd> ^(This option takes a single argument which is a pointer to an
** instance of the [sqlite3_mutex_methods] structure.  The argument specifies
** alternative low-level mutex routines to be used in place
** the mutex routines built into SQLite.)^  ^SQLite makes a copy of the
** content of the [sqlite3_mutex_methods] structure before the call to

# 2011 March 9
#
# 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 tests of the mem5 allocation subsystem.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

ifcapable !mem5 {
  finish_test
  return
}

# The tests in this file configure the lookaside allocator after a 
# connection is opened. This will not work if there is any "presql"
# configured (SQL run within the [sqlite3] wrapper in tester.tcl).
if {[info exists ::G(perm:presql)]} {
  finish_test
  return
}

do_test mem5-1.1 {
  catch {db close}
  sqlite3_shutdown
  sqlite3_config_heap 25000000 0
  sqlite3_config_lookaside 0 0
  sqlite3_initialize
} {SQLITE_OK}

# try with min request size = 2^30
do_test mem5-1.2 {
  catch {db close}
  sqlite3_shutdown
  sqlite3_config_heap 1 1073741824
  sqlite3_config_lookaside 0 0
  sqlite3_initialize
} {SQLITE_NOMEM}

# try with min request size = 2^30+1
# previously this was causing the memsys5Log() func to infinitely loop.
do_test mem5-1.3 {
  catch {db close}
  sqlite3_shutdown
  sqlite3_config_heap 1 1073741825
  sqlite3_config_lookaside 0 0
  sqlite3_initialize
} {SQLITE_NOMEM}

do_test mem5-1.4 {
  catch {db close}
  sqlite3_shutdown
  sqlite3_config_heap 0 0
  sqlite3_config_lookaside 0 0
  sqlite3_initialize
} {SQLITE_OK}

finish_test