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#include <sys/mman.h>
#include <errno.h>
#include <stdckdint.h>
#include <stdlib.h>
#include "_attrs.h"
#include "alloc.h"
#include "macros.h"
#define IS_POW_2(n) ((n) != 0 && ((n) & ((n) - 1)) == 0)
[[_mlib_pure, _mlib_inline]] static size_t pad(size_t, size_t);
static struct _region *mkregion(size_t);
size_t
pad(size_t len, size_t align)
{
return (len + align - 1) & ~(align - 1);
}
struct _region *
mkregion(size_t cap)
{
struct _region *r = malloc(sizeof(struct _region));
if (r == nullptr)
return nullptr;
*r = (struct _region){
.cap = cap,
.data = mmap(nullptr, cap, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0),
};
if (r->data == MAP_FAILED) {
int save = errno;
free(r);
errno = save;
return nullptr;
}
r->last = r->data;
return r;
}
void *
arena_alloc(arena *a, size_t sz, size_t n, size_t align)
{
ASSUME(a != nullptr);
ASSUME(IS_POW_2(align));
if (ckd_mul(&sz, sz, n)) {
errno = EOVERFLOW;
return nullptr;
}
for (struct _region *r = a->_head; r != nullptr; r = r->next) {
size_t nlen, off = pad(r->len, align);
/* Technically there are other ways to solve this… but at this point you
might as well just fail */
if (ckd_add(&nlen, off, sz)) {
errno = EOVERFLOW;
return nullptr;
}
if (nlen <= r->cap) {
void *ret = (char *)r->data + off;
r->len = nlen;
r->last = ret;
return ret;
}
}
/* No page exists with enough space */
struct _region *r = mkregion(MAX(sz, a->_init));
if (r == nullptr)
return nullptr;
r->next = a->_head;
r->len = sz;
a->_head = r;
return r->data;
}
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