310 lines
8.8 KiB
C
310 lines
8.8 KiB
C
/* Memory allocator `malloc'.
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Copyright 1990, 1991 Free Software Foundation
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Written May 1989 by Mike Haertel.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA.
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The author may be reached (Email) at the address mike@ai.mit.edu,
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or (US mail) as Mike Haertel c/o Free Software Foundation. */
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/* IGNORE(@ */
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#include <ansidecl.h>
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#include <stddef.h>
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#include <stdlib.h>
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/* @) */
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#define _MALLOC_INTERNAL
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#include <malloc.h>
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#if defined(__GNU_LIBRARY__) || defined(STDC_HEADERS) || defined(USG)
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#include <string.h>
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#else
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#define memset(s, zero, n) bzero ((s), (n))
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#define memcpy(d, s, n) bcopy ((s), (d), (n))
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#endif
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/* How to really get more memory. */
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PTR EXFUN((*__morecore), (ptrdiff_t __size)) = __default_morecore;
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/* Debugging hook for `malloc'. */
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PTR EXFUN((*__malloc_hook), (size_t __size));
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/* Pointer to the base of the first block. */
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char *_heapbase;
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/* Block information table. Allocated with align/__free (not malloc/free). */
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malloc_info *_heapinfo;
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/* Number of info entries. */
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static size_t heapsize;
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/* Search index in the info table. */
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size_t _heapindex;
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/* Limit of valid info table indices. */
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size_t _heaplimit;
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/* Free lists for each fragment size. */
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struct list _fraghead[BLOCKLOG];
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/* Instrumentation. */
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size_t _chunks_used;
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size_t _bytes_used;
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size_t _chunks_free;
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size_t _bytes_free;
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/* Are you experienced? */
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int __malloc_initialized;
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/* Aligned allocation. */
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static PTR
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DEFUN(align, (size), size_t size)
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{
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PTR result;
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unsigned long int adj;
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result = (*__morecore)(size);
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adj = (unsigned long int) ((unsigned long int) ((char *) result -
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(char *) NULL)) % BLOCKSIZE;
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if (adj != 0)
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{
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adj = BLOCKSIZE - adj;
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(void) (*__morecore)(adj);
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result = (char *) result + adj;
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}
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return result;
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}
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/* Set everything up and remember that we have. */
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static int
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DEFUN_VOID(initialize)
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{
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heapsize = HEAP / BLOCKSIZE;
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_heapinfo = (malloc_info *) align(heapsize * sizeof(malloc_info));
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if (_heapinfo == NULL)
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return 0;
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memset(_heapinfo, 0, heapsize * sizeof(malloc_info));
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_heapinfo[0].free.size = 0;
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_heapinfo[0].free.next = _heapinfo[0].free.prev = 0;
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_heapindex = 0;
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_heapbase = (char *) _heapinfo;
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__malloc_initialized = 1;
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return 1;
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}
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/* Get neatly aligned memory, initializing or
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growing the heap info table as necessary. */
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static PTR
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DEFUN(morecore, (size), size_t size)
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{
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PTR result;
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malloc_info *newinfo, *oldinfo;
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size_t newsize;
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result = align(size);
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if (result == NULL)
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return NULL;
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/* Check if we need to grow the info table. */
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if ((size_t) BLOCK((char *) result + size) > heapsize)
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{
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newsize = heapsize;
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while ((size_t) BLOCK((char *) result + size) > newsize)
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newsize *= 2;
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newinfo = (malloc_info *) align(newsize * sizeof(malloc_info));
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if (newinfo == NULL)
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{
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(*__morecore)(- size);
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return NULL;
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}
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memset(newinfo, 0, newsize * sizeof(malloc_info));
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memcpy(newinfo, _heapinfo, heapsize * sizeof(malloc_info));
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oldinfo = _heapinfo;
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newinfo[BLOCK(oldinfo)].busy.type = 0;
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newinfo[BLOCK(oldinfo)].busy.info.size
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= BLOCKIFY(heapsize * sizeof(malloc_info));
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_heapinfo = newinfo;
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__free(oldinfo);
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heapsize = newsize;
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}
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_heaplimit = BLOCK((char *) result + size);
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return result;
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}
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/* Allocate memory from the heap. */
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PTR
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DEFUN(malloc, (size), size_t size)
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{
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PTR result;
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size_t block, blocks, lastblocks, start;
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register size_t i;
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struct list *next;
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if (size == 0)
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return NULL;
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if (__malloc_hook != NULL)
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return (*__malloc_hook)(size);
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if (!__malloc_initialized)
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if (!initialize())
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return NULL;
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if (size < sizeof(struct list))
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size = sizeof(struct list);
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/* Determine the allocation policy based on the request size. */
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if (size <= BLOCKSIZE / 2)
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{
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/* Small allocation to receive a fragment of a block.
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Determine the logarithm to base two of the fragment size. */
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register size_t log = 1;
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--size;
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while ((size /= 2) != 0)
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++log;
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/* Look in the fragment lists for a
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free fragment of the desired size. */
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next = _fraghead[log].next;
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if (next != NULL)
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{
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/* There are free fragments of this size.
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Pop a fragment out of the fragment list and return it.
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Update the block's nfree and first counters. */
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result = (PTR) next;
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next->prev->next = next->next;
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if (next->next != NULL)
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next->next->prev = next->prev;
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block = BLOCK(result);
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if (--_heapinfo[block].busy.info.frag.nfree != 0)
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_heapinfo[block].busy.info.frag.first = (unsigned long int)
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((unsigned long int) ((char *) next->next - (char *) NULL)
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% BLOCKSIZE) >> log;
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/* Update the statistics. */
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++_chunks_used;
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_bytes_used += 1 << log;
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--_chunks_free;
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_bytes_free -= 1 << log;
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}
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else
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{
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/* No free fragments of the desired size, so get a new block
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and break it into fragments, returning the first. */
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result = malloc(BLOCKSIZE);
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if (result == NULL)
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return NULL;
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/* Link all fragments but the first into the free list. */
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for (i = 1; i < (size_t) (BLOCKSIZE >> log); ++i)
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{
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next = (struct list *) ((char *) result + (i << log));
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next->next = _fraghead[log].next;
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next->prev = &_fraghead[log];
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next->prev->next = next;
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if (next->next != NULL)
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next->next->prev = next;
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}
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/* Initialize the nfree and first counters for this block. */
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block = BLOCK(result);
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_heapinfo[block].busy.type = log;
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_heapinfo[block].busy.info.frag.nfree = i - 1;
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_heapinfo[block].busy.info.frag.first = i - 1;
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_chunks_free += (BLOCKSIZE >> log) - 1;
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_bytes_free += BLOCKSIZE - (1 << log);
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_bytes_used -= BLOCKSIZE - (1 << log);
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}
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}
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else
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{
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/* Large allocation to receive one or more blocks.
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Search the free list in a circle starting at the last place visited.
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If we loop completely around without finding a large enough
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space we will have to get more memory from the system. */
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blocks = BLOCKIFY(size);
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start = block = MALLOC_SEARCH_START;
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while (_heapinfo[block].free.size < blocks)
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{
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block = _heapinfo[block].free.next;
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if (block == start)
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{
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/* Need to get more from the system. Check to see if
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the new core will be contiguous with the final free
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block; if so we don't need to get as much. */
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block = _heapinfo[0].free.prev;
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lastblocks = _heapinfo[block].free.size;
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if (_heaplimit != 0 && block + lastblocks == _heaplimit &&
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(*__morecore)(0) == ADDRESS(block + lastblocks) &&
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(morecore((blocks - lastblocks) * BLOCKSIZE)) != NULL)
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{
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_heapinfo[block].free.size = blocks;
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_bytes_free += (blocks - lastblocks) * BLOCKSIZE;
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continue;
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}
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result = morecore(blocks * BLOCKSIZE);
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if (result == NULL)
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return NULL;
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block = BLOCK(result);
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_heapinfo[block].busy.type = 0;
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_heapinfo[block].busy.info.size = blocks;
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++_chunks_used;
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_bytes_used += blocks * BLOCKSIZE;
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return result;
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}
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}
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/* At this point we have found a suitable free list entry.
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Figure out how to remove what we need from the list. */
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result = ADDRESS(block);
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if (_heapinfo[block].free.size > blocks)
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{
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/* The block we found has a bit left over,
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so relink the tail end back into the free list. */
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_heapinfo[block + blocks].free.size
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= _heapinfo[block].free.size - blocks;
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_heapinfo[block + blocks].free.next
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= _heapinfo[block].free.next;
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_heapinfo[block + blocks].free.prev
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= _heapinfo[block].free.prev;
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_heapinfo[_heapinfo[block].free.prev].free.next
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= _heapinfo[_heapinfo[block].free.next].free.prev
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= _heapindex = block + blocks;
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}
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else
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{
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/* The block exactly matches our requirements,
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so just remove it from the list. */
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_heapinfo[_heapinfo[block].free.next].free.prev
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= _heapinfo[block].free.prev;
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_heapinfo[_heapinfo[block].free.prev].free.next
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= _heapindex = _heapinfo[block].free.next;
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--_chunks_free;
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}
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_heapinfo[block].busy.type = 0;
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_heapinfo[block].busy.info.size = blocks;
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++_chunks_used;
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_bytes_used += blocks * BLOCKSIZE;
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_bytes_free -= blocks * BLOCKSIZE;
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}
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return result;
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}
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