157 lines
4 KiB
C
157 lines
4 KiB
C
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/***
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*heapsrch.c - search the heap for a free block
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*
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* Copyright (c) 1989-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Defines the _heap_search() function.
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*
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*Revision History:
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* 06-30-89 GJF Module created. Yea, it's ugly, but it seems to work.
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* 07-21-89 GJF Now assumes proverdesc points to the descriptor for
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* first free block in the heap, if any, or is plastdesc,
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* if there are no free blocks
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* 11-08-89 GJF Fixed copyright, added register attribute to vars
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* 12-18-89 GJF Removed some redundant code, updated the description,
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* changed include file name to heap.h, added explicit
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* _cdecl to function definition.
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* 12-19-89 GJF Got rid of code to maintain plastdesc
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* 03-11-90 GJF Replaced _cdecl with _CALLTYPE1, added #include
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* <cruntime.h> and removed #include <register.h>.
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* 09-28-90 GJF New-style function declarator.
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* 03-05-91 GJF Changed strategy for rover - old version available
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* by #define-ing _OLDROVER_.
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* 04-06-93 SKS Replace _CRTAPI* with __cdecl
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* 02-08-95 GJF Removed obsolete _OLDROVER_ support.
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* 04-30-95 GJF Made conditional on WINHEAP.
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*
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*******************************************************************************/
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#ifndef WINHEAP
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#include <cruntime.h>
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#include <heap.h>
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#include <stddef.h>
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#define LOOP_FOREVER while(1)
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/***
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*_PBLKDESC _heap_search(unsigned size) - Find a free block of a least size
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* bytes.
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*
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*Purpose:
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* Finds a free block of at least size bytes. Searches the list of block
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* descriptors from *proverdesc to the end (marked by the sentinel). The
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* search is strictly first fit. Adjacent free blocks are coalesced as
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* they are encountered during the search.
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*
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*Entry:
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* unsigned size - size of block requested
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*
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*Exit:
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* Success: Pointer to descriptor for free memory block of at least size
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* bytes
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* Failure: NULL
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*
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*Uses:
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*
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*Exceptions:
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*
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*******************************************************************************/
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_PBLKDESC __cdecl _heap_search (
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unsigned size
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)
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{
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REG1 _PBLKDESC pdesc;
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REG2 _PBLKDESC pdesc2;
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_PBLKDESC pretdesc = NULL;
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/* search from proverdesc thru plastdesc, looking for free block of
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* at least size bytes. coalesce adjacent free blocks during the
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* search. the search is strictly first fit. that is, it terminates
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* when the first block is found of adequate size.
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*/
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for ( pdesc = _heap_desc.proverdesc ; pdesc != &(_heap_desc.sentinel) ;
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pdesc = pdesc->pnextdesc )
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/* is pdesc free?
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*/
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if ( _IS_FREE(pdesc) )
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/* coalesce loop
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*/
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LOOP_FOREVER {
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/* if pdesc is big enough, return it
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*/
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if ( _BLKSIZE(pdesc) >= size ) {
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pretdesc = pdesc;
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goto searchdone;
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}
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/* see if the next block is free and, if so,
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* coalesce it with pdesc
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*/
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pdesc2 = pdesc->pnextdesc;
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if ( _IS_FREE(pdesc2) ) {
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/* coalesce pdesc2 with pdesc
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*/
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pdesc->pnextdesc = pdesc2->pnextdesc;
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_PUTEMPTY(pdesc2);
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}
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else
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break;
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} /* end LOOP_FOREVER */
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for ( pdesc = _heap_desc.pfirstdesc ; pdesc != _heap_desc.proverdesc ;
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pdesc = pdesc->pnextdesc )
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/* is pdesc free?
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*/
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if ( _IS_FREE(pdesc) )
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/* coalesce loop
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*/
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LOOP_FOREVER {
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/* if pdesc is big enough, return it
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*/
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if ( _BLKSIZE(pdesc) >= size ) {
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pretdesc = pdesc;
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goto searchdone;
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}
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/* see if the next block is free and, if so,
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* coalesce it with pdesc
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*/
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pdesc2 = pdesc->pnextdesc;
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if ( _IS_FREE(pdesc2) ) {
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/* coalesce pdesc2 with pdesc
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*/
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pdesc->pnextdesc = pdesc2->pnextdesc;
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_PUTEMPTY(pdesc2);
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/* special handling for the case where
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* the rover has been coalesced (search
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* ends)
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*/
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if ( _heap_desc.proverdesc == pdesc2 )
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{
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_heap_desc.proverdesc = pdesc;
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if ( _BLKSIZE(pdesc) >= size )
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pretdesc = pdesc;
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goto searchdone;
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}
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}
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else
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break;
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} /* end LOOP_FOREVER */
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searchdone:
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/* common exit for all code paths. win, lose or draw, this is the
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* only code path back to the caller.
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*/
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return(pretdesc);
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}
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#endif /* WINHEAP */
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