malloc.c

unix v7是最后一个广泛发布的研究型UNIX版本

#include "../h/param.h"
#include "../h/systm.h"
#include "../h/map.h"

/*
 * Allocate 'size' units from the given
 * map. Return the base of the allocated
 * space.
 * In a map, the addresses are increasing and the
 * list is terminated by a 0 size.
 * The core map unit is 64 bytes; the swap map unit
 * is 512 bytes.
 * Algorithm is first-fit.
 */
malloc(mp, size)
struct map *mp;
{
	register unsigned int a;
	register struct map *bp;

	for (bp=mp; bp->m_size; bp++) {
		if (bp->m_size >= size) {
			a = bp->m_addr;
			bp->m_addr += size;
			if ((bp->m_size -= size) == 0) {
				do {
					bp++;
					(bp-1)->m_addr = bp->m_addr;
				} while ((bp-1)->m_size = bp->m_size);
			}
			return(a);
		}
	}
	return(0);
}

/*
 * Free the previously allocated space aa
 * of size units into the specified map.
 * Sort aa into map and combine on
 * one or both ends if possible.
 */
mfree(mp, size, a)
struct map *mp;
register int a;
{
	register struct map *bp;
	register unsigned int t;

	if ((bp = mp)==coremap && runin) {
		runin = 0;
		wakeup((caddr_t)&runin);	/* Wake scheduler when freeing core */
	}
	for (; bp->m_addr<=a && bp->m_size!=0; bp++);
	if (bp>mp && (bp-1)->m_addr+(bp-1)->m_size == a) {
		(bp-1)->m_size += size;
		if (a+size == bp->m_addr) {
			(bp-1)->m_size += bp->m_size;
			while (bp->m_size) {
				bp++;
				(bp-1)->m_addr = bp->m_addr;
				(bp-1)->m_size = bp->m_size;
			}
		}
	} else {
		if (a+size == bp->m_addr && bp->m_size) {
			bp->m_addr -= size;
			bp->m_size += size;
		} else if (size) {
			do {
				t = bp->m_addr;
				bp->m_addr = a;
				a = t;
				t = bp->m_size;
				bp->m_size = size;
				bp++;
			} while (size = t);
		}
	}
}