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344 lines
16 KiB
C
344 lines
16 KiB
C
/****************************************************************************
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*
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* Open Watcom Project
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*
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* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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*
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* ========================================================================
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*
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* This file contains Original Code and/or Modifications of Original
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* Code as defined in and that are subject to the Sybase Open Watcom
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* Public License version 1.0 (the 'License'). You may not use this file
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* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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* provided with the Original Code and Modifications, and is also
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* available at www.sybase.com/developer/opensource.
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*
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* The Original Code and all software distributed under the License are
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* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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* NON-INFRINGEMENT. Please see the License for the specific language
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* governing rights and limitations under the License.
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*
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* ========================================================================
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*
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* Description: Heart of the heap manager. Do not break
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* unless you have a death wish.
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*
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****************************************************************************/
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#include "variety.h"
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#include <limits.h>
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#include <malloc.h>
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#include "heap.h"
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#if defined(M_I86)
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extern unsigned setup_ds( unsigned );
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#pragma aux setup_ds = \
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"push ax" \
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"mov ax,ds" \
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"pop ds" \
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parm [ax] value [ax];
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#define setup_segment( _x ) _x = setup_ds( _x );
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#else
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#define setup_segment( _x ) (void)(_x = _x);
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#endif
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//
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// input:
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// size - #bytes to allocate
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// segment - 16bit Intel data selector containing heap
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// offset - address of heap control block
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// if 16bit Intel -> offset within segment
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// else -> absolute pointer value
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//
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// output:
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// result - address of allocated storage or zero on failure
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// if 16bit Intel -> offset within segment
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// else -> absolute pointer value
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//
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unsigned __MemAllocator( unsigned size, unsigned segment, unsigned offset )
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{
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frlptr result;
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result = 0; // assume the worst
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setup_segment( segment ); // setup DS for 16bit Intel
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if( size != 0 ) { // quit if size is zero
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unsigned new_size;
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new_size = size + TAG_SIZE + ROUND_SIZE;// round up size
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if( new_size >= size ) { // quit if overflowed
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struct heapblkp _WCI86NEAR *heap;
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unsigned largest;
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heap = (struct heapblkp _WCI86NEAR *)offset;
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size = new_size & ~ROUND_SIZE; // make size even
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largest = heap->largest_blk;
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if( size < FRL_SIZE ) {
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size = FRL_SIZE;
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}
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if( size <= largest ) { // quit if size too big
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frlptr pcur;
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unsigned len;
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pcur = heap->rover; // start at rover
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largest = heap->b4rover;
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if( size <= largest ) { // check size with rover
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pcur = heap->freehead.next; // start at beginning
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largest = 0; // reset largest block size
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}
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for(;;) { // search free list
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len = pcur->len;
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if( size <= len ) { // found one
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break;
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}
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if( len > largest ) { // update largest block size
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largest = len;
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}
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pcur = pcur->next; // advance to next entry
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if( pcur == // if back at start
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(frlptr)&(heap->freehead)) {
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heap->largest_blk = largest; // update largest
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setup_segment( segment ); // 16bit Intel restore
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return( (unsigned)result ); // return 0
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}
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}
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heap->b4rover = largest; // update rover size
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heap->numalloc++; // udpate allocation count
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len -= size; // compute leftover size
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if( len >= FRL_SIZE ) { // if leftover big enough
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// split into two chunks
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frlptr pprev; // before current
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frlptr pnext; // after current
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frlptr pnew; // start of new piece
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pnew = (frlptr)((PTR)pcur + size);
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heap->rover = pnew; // update rover
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pnew->len = len; // set new size
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pcur->len = size; // reset current size
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pprev = pcur->prev; // update next/prev links
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pnew->prev = pprev;
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pnext = pcur->next;
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pnew->next = pnext;
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pprev->next = pnew;
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pnext->prev = pnew;
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} else { // just use this chunk
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frlptr pprev; // before current
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frlptr pnext; // after current
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heap->numfree--; // 1 fewer entries in free list
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pprev = pcur->prev;
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heap->rover = pprev; // update rover
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pnext = pcur->next; // update next/prev links
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pprev->next = pnext;
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pnext->prev = pprev;
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}
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pcur->len |= 1; // mark as allocated
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// get pointer to user area
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result = (frlptr)((PTR)pcur + TAG_SIZE);
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}
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}
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}
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setup_segment( segment ); // 16bit Intel restore
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return( (unsigned)result );
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}
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//
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// input:
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// pointer - address of block to free
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// if 16bit Intel -> offset within segment
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// else -> absolute pointer value
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// segment - 16bit Intel data selector containing heap
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// offset - address of heap control block
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// if 16bit Intel -> offset within segment
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// else -> absolute pointer value
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//
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// output:
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// none
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//
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void __MemFree( unsigned pointer, unsigned segment, unsigned offset )
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{
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setup_segment( segment ); // setup DS for 16bit Intel
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if( pointer != 0 ) { // quit if pointer is zero
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frlptr pfree;
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pfree = (frlptr)(pointer - TAG_SIZE);
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if( pfree->len & 1 ) { // quit if storage is free
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struct heapblkp _WCI86NEAR *heap;
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frlptr pnext;
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frlptr pprev;
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frlptr ptr;
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unsigned len;
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heap = (struct heapblkp _WCI86NEAR *)offset;
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do { // this allows break statement
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unsigned average;
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unsigned numfree;
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// look at next block to try and coalesce
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len = pfree->len & ~1; // get next block
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pnext = (frlptr)((PTR)pfree + len);
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if( (pnext->len & 1) == 0 ) { // if it is free
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len += pnext->len; // include the length
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pfree->len = len; // update pfree length
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if( pnext == heap->rover ) { // check for rover
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heap->rover = pfree; // update rover
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}
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pprev = pnext->prev; // fixup next/prev links
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pnext = pnext->next;
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pprev->next = pnext;
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pnext->prev = pprev;
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heap->numfree--; // reduce numfree
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break; // proceed to coalesce code
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}
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// following block is not free
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// we must now try to figure out where pfree
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// is in relation to the entries in the free list
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pfree->len = len; // remove allocated marker
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// check a few special places
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// see if pfree is:
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// - just before or just after the rover
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// - at the very beginning or very end of the heap
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pnext = heap->rover; // get rover
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if( pfree < pnext ) { // where is pfree?
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// pfree is before rover
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if( pfree > pnext->prev ) { // where is pfree?
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// pfree is next to rover
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break; // proceed to coalesce code
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}
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pnext = heap->freehead.next; // get start of free list
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if( pfree < pnext ) { // where is pfree?
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// pfree is at start of list
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break; // proceed to coalesce code
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}
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} else { // pfree is after rover
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pnext = pnext->next; // pnext is after rover
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if( pfree < pnext ) { // where is pfree?
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// pfree is just after rover
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break; // proceed to coalesce code
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}
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// get end of free list
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pnext = (frlptr)&(heap->freehead);
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pprev = pnext->prev;
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if( pfree > pprev ) { // where is pfree?
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// pfree is at end of list
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break; // proceed to coalesce code
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}
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}
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// Calculate the average number of allocated blocks we may
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// have to skip until we expect to find a free block. If
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// this number is less than the total number of free blocks,
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// chances are that we can find the correct position in the
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// free list by scanning ahead for a free block and linking
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// this free block before the found free block. We protect
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// ourself against the degenerate case where there is an
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// extremely long string of allocated blocks by limiting the
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// number of blocks we will search to twice the calculated
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// average.
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numfree = heap->numfree;
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average = heap->numalloc / (numfree+1);
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if( average < numfree ) {
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// There are lots of allocated blocks and lots of free
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// blocks. On average we should find a free block
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// quickly by following the allocated blocks, but the
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// worst case can be very bad. So, we try scanning the
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// allocated blocks and give up once we have looked at
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// twice the average.
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unsigned worst;
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worst = heap->numalloc - numfree;
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average *= 2; // give up after this many
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if( worst <= numfree ) {
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average = UINT_MAX; // we won't give up loop
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}
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// point at next allocated
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pnext = (frlptr)((PTR)pfree + pfree->len);
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for(;;) {
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len = pnext->len;
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if( len & 1 ) { // pnext is allocated
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if( len != END_TAG ) { // check for end TAG
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len &= ~1; // advance pnext
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pnext = (frlptr)((PTR)pnext + len);
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average--;
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if( !average ) { // give up search
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break;
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}
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} else {
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break; // stop at end tag
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}
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} else {
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// break twice!
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goto found_it; // we have the spot
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}
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}
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}
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// when all else fails, search the free list
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pnext = heap->rover; // begin at rover
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if( pfree < pnext ) { // is pfree before rover?
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// then begin at start
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pnext = heap->freehead.next;
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}
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for(;;) {
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if( pfree < pnext ) { // if pfree before pnext
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break; // we found it
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}
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pnext = pnext->next; // advance pnext
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if( pfree < pnext ) { // if pfree before pnext
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break; // we found it
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}
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pnext = pnext->next; // advance pnext
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if( pfree < pnext ) { // if pfree before pnext
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break; // we found it
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}
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pnext = pnext->next; // advance pnext
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}
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} while( 0 ); // only do once
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found_it:
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// if we are here, then we found the spot
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pprev = pnext->prev; // setup pprev
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// pprev, pfree, pnext are all setup
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len = pfree->len;
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// check pprev and pfree
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ptr = (frlptr)((PTR)pprev + pprev->len);
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if( ptr == pfree ) { // are they adjacent?
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// coalesce pprev and pfree
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len += pprev->len; // udpate len
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pprev->len = len;
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if( heap->rover == pfree ) { // check rover impact
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heap->rover = pprev; // update rover
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}
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pfree = pprev; // now work with coalesced blk
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} else {
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heap->numfree++; // one more free entry
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pfree->next = pnext; // update next/prev entries
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pfree->prev = pprev;
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pprev->next = pfree;
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pnext->prev = pfree;
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}
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heap->numalloc--; // one fewer allocated
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if( pfree < heap->rover ) { // check rover impact
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if( len > heap->b4rover ) { // is len bigger than b4rover
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heap->b4rover = len; // then update b4rover
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}
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}
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if( len > heap->largest_blk ) { // check largest block
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heap->largest_blk = len;
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}
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}
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}
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setup_segment( segment ); // 16bit Intel restore
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}
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