179 lines
5.3 KiB
C
179 lines
5.3 KiB
C
/***************************************************************************
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* Copyright 1995, Technion, Israel Institute of Technology
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* Electrical Eng, Software Lab.
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* Author: Michael Veksler.
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***************************************************************************
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* File: shm_fragment.c
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* Purpose: Data fragments and free list items. Allocate and free blocks.
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***************************************************************************
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*/
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#include <stdio.h> /* for debugging only */
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#include <stddebug.h>
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#include <debug.h> /* for "stddeb" */
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#include "shm_fragment.h"
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#include "shm_block.h"
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/******************************************************************************
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*
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* Free list: all fragments are ordered according to memory location.
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* new fragments are inserted in this way.
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*
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******************************************************************************
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*/
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#define FRAG_PTR(block,ofs) ((struct shm_fragment *) ((char *) block + ofs) )
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#define NEXT_FRAG(block,ofs) ( FRAG_PTR(block,ofs)->info.next )
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/* setup first item in the free list */
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void shm_FragmentInit(struct shm_block *block,int first, int size)
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{
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struct shm_fragment *fragment;
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/* round up to nearest 16 byte boundary */
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first=(first+15)& ~15;
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block->free_list=first;
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/* make all the block (exluding the header) free */
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fragment= FRAG_PTR(block, first);
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block->free= fragment->size= size-first;
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fragment->info.next=0;
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}
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void shm_FragPtrFree(struct shm_block *block, void *ptr)
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{
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/* ptr points to fragment->info.data, find pointer to fragment,
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* find the offset of this pointer in block.
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*/
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if (ptr)
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shm_FragmentFree(block, PTR2REL(block, ptr));
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}
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void shm_FragmentFree(struct shm_block *block, int fragment_ofs)
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{
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struct shm_fragment *fragment=NULL;
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int prev;
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int next;
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fragment_ofs-=(int )&fragment->info.data;
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fragment= FRAG_PTR(block, fragment_ofs);
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block->free+=fragment->size;
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/* scan free list to find candidates for merging with fragment */
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for (prev=0, next=block->free_list;
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(next!=0) && (fragment_ofs > next) ;
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prev=next, next=NEXT_FRAG(block,next) )
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;
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/* insert fragment between, prev and next
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* prev==0: fragment will be the first item in free list
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* next==0: fragment will be the last item in free list
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*/
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/* update fragment (point to next, or merge with next) */
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if ( fragment_ofs+fragment->size == next ) {
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/* merge with the next free block */
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fragment->size+= FRAG_PTR(block,next)->size;
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fragment->info.next=FRAG_PTR(block,next)->info.next;
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} else
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/* fragment should be inserted before the next fragment or end of */
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/* list. (not merged) */
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fragment->info.next=next;
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/* now fragment has all the information about the rest of the list */
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/* upate prev fragment (point or merge with fragment) */
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if (prev==0) /* first item in free list */
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block->free_list=fragment_ofs;
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else if ( prev+FRAG_PTR(block,prev)->size == fragment_ofs ) {
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/* merge fragment with previous fragment */
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FRAG_PTR(block,prev)->size+= fragment->size;
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FRAG_PTR(block,prev)->info.next=fragment->info.next;
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} else
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/* insert fragment after previous fragment */
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FRAG_PTR(block,prev)->info.next=fragment_ofs;
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}
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/* use "first fit" algorithm,
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* return: offset to data in fragment.
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*/
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int shm_FragmentAlloc(struct shm_block *block, int size)
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{
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int prev;
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int candidate;
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struct shm_fragment *fragment;
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struct shm_fragment *ret_fragment;
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if (size <= 0)
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return NIL;
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/* add size of "fragment->size" */
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size+= (char *)&fragment->info.data - (char *)fragment ;
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/* round "size" to nearest 16 byte value */
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size= (size+15) & ~15;
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if (size > block->free)
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return NIL;
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/* scan free list to find candidates for allocation */
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for (prev=0, candidate=block->free_list;
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candidate!=0 ;
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prev=candidate, candidate= fragment->info.next )
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{
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fragment=FRAG_PTR(block,candidate);
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if (fragment->size >= size)
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break;
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}
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if (candidate == 0)
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return NIL;
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block->free-=size;
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if (fragment->size == size) {
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if (prev == 0)
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block->free_list= fragment->info.next;
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else
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FRAG_PTR(block,prev)->info.next= fragment->info.next;
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return PTR2REL(block, &fragment->info.data);
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}
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/* fragment->size > size */
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/* Split fragment in two, return one part, put the other in free list. */
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/* The part that starts at the old location - will stay in the free list. */
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fragment->size -= size;
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ret_fragment=FRAG_PTR(block, candidate + fragment->size);
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ret_fragment->size= size;
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return PTR2REL(block, ret_fragment->info.data);
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}
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/* like shm_FragmentAlloc, returns pointer instead of offset */
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char *shm_FragPtrAlloc(struct shm_block *block, int size)
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{
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int ofs;
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ofs= shm_FragmentAlloc(block,size);
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if (ofs == NIL)
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return NULL;
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else
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return (char *) REL2PTR(block, ofs);
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}
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/* This is used for debugging only */
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void shm_print_free_list(struct shm_block *block)
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{
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struct shm_fragment *fragment;
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int item;
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item=block->free_list;
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if (item==0) {
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fprintf(stddeb,"no free fragments");
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} else {
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for (; item ; item=fragment->info.next) {
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fragment=FRAG_PTR(block,item);
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fprintf(stddeb,"{0x%04x,0x%04x} ",item,fragment->size);
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}
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}
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fprintf(stddeb," [total free=%04x]\n",block->free);
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fflush(stddeb);
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}
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