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#include "types.h"
#include "stat.h"
#include "user.h"
#include "param.h"
// Memory allocator by Kernighan and Ritchie, The C programming Language,
// 2nd ed. Section 8.7.
typedef long Align;
union header {
struct {
union header *ptr;
uint size;
} s;
Align x;
};
typedef union header Header;
static Header base;
static Header *freep = 0;
void
free(void *ap)
{
Header *bp, *p;
bp = (Header *) ap - 1;
for (p = freep; !(bp > p && bp < p->s.ptr); p = p->s.ptr)
if (p >= p->s.ptr && (bp > p || bp < p->s.ptr))
break;
if (bp + bp->s.size == p->s.ptr) {
bp->s.size += p->s.ptr->s.size;
bp->s.ptr = p->s.ptr->s.ptr;
} else
bp->s.ptr = p->s.ptr;
if (p + p->s.size == bp) {
p->s.size += bp->s.size;
p->s.ptr = bp->s.ptr;
} else
p->s.ptr = bp;
freep = p;
}
static Header *
morecore(uint nu)
{
char *cp;
Header *up;
if (nu < PAGE)
nu = PAGE;
cp = sbrk(nu * sizeof(Header));
if (cp == (char *) -1)
return 0;
up = (Header *) cp;
up->s.size = nu;
free((void *)(up + 1));
return freep;
}
void *
malloc(uint nbytes)
{
Header *p, *prevp;
uint nunits;
nunits = (nbytes + sizeof(Header) - 1)/sizeof(Header) + 1;
if ((prevp = freep) == 0) {
base.s.ptr = freep = prevp = &base;
base.s.size = 0;
}
for (p = prevp->s.ptr; ; prevp = p, p = p->s.ptr) {
if (p->s.size >= nunits) {
if (p->s.size == nunits)
prevp->s.ptr = p->s.ptr;
else {
p->s.size -= nunits;
p += p->s.size;
p->s.size = nunits;
}
freep = prevp;
return (void *) (p + 1);
}
if (p == freep)
if ((p = morecore(nunits)) == 0)
return 0;
}
}
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