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/*

 *  Heap Handler

 *

 *  COPYRIGHT (c) 1989-1999.

 *  On-Line Applications Research Corporation (OAR).

 *

 *  The license and distribution terms for this file may be

 *  found in the file LICENSE in this distribution or at

 *  http://www.OARcorp.com/rtems/license.html.

 *

 *  heapallocate.c,v 1.3 2000/11/28 21:47:39 joel Exp

 */

#include <rtems/system.h>

#include <rtems/score/sysstate.h>

#include <rtems/score/heap.h>

/*PAGE

 *

 *  _Heap_Allocate

 *

 *  This kernel routine allocates the requested size of memory

 *  from the specified heap.

 *

 *  Input parameters:

 *    the_heap  - pointer to heap header.

 *    size      - size in bytes of the memory block to allocate.

 *

 *  Output parameters:

 *    returns - starting address of memory block allocated

 */

void *_Heap_Allocate(

  Heap_Control        *the_heap,

  unsigned32           size

)

{

  unsigned32  excess;

  unsigned32  the_size;

  Heap_Block *the_block;

  Heap_Block *next_block;

  Heap_Block *temporary_block;

  void       *ptr;

  unsigned32  offset;

  /*

   * Catch the case of a user allocating close to the limit of the

   * unsigned32.

   */

  if ( size >= (-1 - HEAP_BLOCK_USED_OVERHEAD) )

    return( NULL );

  excess   = size % the_heap->page_size;

  the_size = size + the_heap->page_size + HEAP_BLOCK_USED_OVERHEAD;

  if ( excess )

    the_size += the_heap->page_size - excess;

  if ( the_size < sizeof( Heap_Block ) )

    the_size = sizeof( Heap_Block );

  for ( the_block = the_heap->first;

        ;

        the_block = the_block->next ) {

    if ( the_block == _Heap_Tail( the_heap ) )

      return( NULL );

    if ( the_block->front_flag >= the_size )

      break;

  }

  if ( (the_block->front_flag - the_size) >

       (the_heap->page_size + HEAP_BLOCK_USED_OVERHEAD) ) {

    the_block->front_flag -= the_size;

    next_block             = _Heap_Next_block( the_block );

    next_block->back_flag  = the_block->front_flag;

    temporary_block            = _Heap_Block_at( next_block, the_size );

    temporary_block->back_flag =

    next_block->front_flag     = _Heap_Build_flag( the_size,

                                    HEAP_BLOCK_USED );

    ptr = _Heap_Start_of_user_area( next_block );

  } else {

    next_block                = _Heap_Next_block( the_block );

    next_block->back_flag     = _Heap_Build_flag( the_block->front_flag,

                                   HEAP_BLOCK_USED );

    the_block->front_flag     = next_block->back_flag;

    the_block->next->previous = the_block->previous;

    the_block->previous->next = the_block->next;

    ptr = _Heap_Start_of_user_area( the_block );

  }

  /*

   * round ptr up to a multiple of page size

   * Have to save the bump amount in the buffer so that free can figure it out

   */

  offset = the_heap->page_size - (((unsigned32) ptr) & (the_heap->page_size - 1));

  ptr = _Addresses_Add_offset( ptr, offset );

  *(((unsigned32 *) ptr) - 1) = offset;

#ifdef RTEMS_DEBUG

  {

      unsigned32 ptr_u32;

      ptr_u32 = (unsigned32) ptr;

      if (ptr_u32 & (the_heap->page_size - 1))

          abort();

  }

#endif

  return ptr;

}