#include "alloc.h"

#include <errno.h>
#include <limits.h>
#include <stdlib.h>

#include "byte.h"

#define ALIGNMENT 16   /* XXX: assuming that this alignment is enough */
#define SPACE     4096 /* must be multiple of ALIGNMENT */

typedef union {
  char irrelevant[ALIGNMENT];
  double d;
} aligned;
static aligned realspace[SPACE / ALIGNMENT];
#define space ((char *)realspace)
static unsigned int avail = SPACE; /* multiple of ALIGNMENT; 0<=avail<=SPACE */

/*@null@*/ /*@out@*/ char *alloc(unsigned int n)
{
  char *x;

  /* Guninski exploit + patch from Qualys (CVE-2005-1513) */

  if (n >= (INT_MAX >> 3)) {
    errno = ENOMEM;
    return 0;
  }

  n = ALIGNMENT + n - (n & (ALIGNMENT - 1)); /* XXX: could overflow */
  if (n <= avail) {
    avail -= n;
    return space + avail;
  }
  x = malloc(n);
  if (!x) errno = ENOMEM;
  return x;
}

void alloc_free(char *x)
{
  if (x >= space)
    if (x < space + SPACE) return; /* XXX: assuming that pointers are flat */
  free(x);
}

int alloc_re(char **x, unsigned int m, unsigned int n)
{
  char *y;

  y = alloc(n);
  if (!y) return 0;
  byte_copy(y, m, *x);
  qfree(*x);
  *x = y;
  return 1;
}