malloc.c

mips架构的bootloader,99左右的版本 但源代码现在没人更新了

/*************************************************************
 * File: lib/malloc.c
 * Purpose: Part of C runtime library
 * Author: Phil Bunce ([e-mail])
 * Revision History:
 *	970304	Start of revision history
 */

typedef double ALIGN;

union header {
	struct {
		union header *ptr;
		unsigned size;
		} s;
	ALIGN x;
	};

typedef union header HEADER;

static HEADER base;
static HEADER *allocp; /* K&R called allocp, freep */

#define NULL   0
#define NALLOC 128

/* The rest of this file is from pages 185-189 of K & R Edition 2 */

void *malloc(nbytes)
unsigned long nbytes;
{
	HEADER *morecore();
	register HEADER *p, *q; /* K&R called q, prevp */
	register unsigned nunits;

	nunits = (nbytes + sizeof(HEADER)-1)/sizeof(HEADER)+1;
	if ((q=allocp) == NULL) { /* no free list yet */
		base.s.ptr = allocp = q = &base;
		base.s.size = 0;
	}
	for (p=q->s.ptr; ; q=p, p = p->s.ptr) {
		if (p->s.size >= nunits) { /* big enough */
			if (p->s.size == nunits) /* exactly */
				q->s.ptr = p->s.ptr;
			else {		/* allocate tail end */
				p->s.size -= nunits;
				p += p->s.size;
				p->s.size = nunits;
			}
			allocp = q;
			return((char *) (p+1));
		}
		if (p==allocp)
			if ((p = morecore(nunits)) == NULL)
				return(NULL);
	}
}

HEADER *morecore(nu)
unsigned nu;
{
	char *sbrk();
	register char *cp;
	register HEADER *up;
	register int rnu;
	
	rnu = NALLOC * ((nu+NALLOC-1) / NALLOC);
	cp = sbrk(rnu * sizeof(HEADER));
	if ((int)cp == NULL)
		return(NULL);
	up = (HEADER *)cp;
	up->s.size = rnu;
	free((char *)(up+1));
	return(allocp);
}


free(ap)
char *ap;
{
	register HEADER *p, *q;

	p = (HEADER *)ap - 1;
	for (q=allocp; !(p > q && p < q->s.ptr); q=q->s.ptr)
		if (q >= q->s.ptr && (p > q || p < q->s.ptr))
			break;
	if (p+p->s.size == q->s.ptr) {
		p->s.size += q->s.ptr->s.size;
		p->s.ptr = q->s.ptr->s.ptr;
	} else
		p->s.ptr = q->s.ptr;
	if (q+q->s.size == p) {
		q->s.size += p->s.size;
		q->s.ptr = p->s.ptr;
	} else
		q->s.ptr = p;
	allocp = q;
}

allocsize(ap)
char *ap;
{
register HEADER *p;

p = (HEADER *)ap - 1;
return(p->s.size*sizeof(HEADER));
}