#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include "byte.h"
#include "alloc.h"

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

/**
  * @file alloc.c
  * @authors djb, feh, jmh
  * @ref qmail
  * @brief Generic allocation of heap memory
  */

typedef union { 
	char irrelevant[ALIGNMENT]; 
	double d; 
} aligned;

static aligned realspace[SPACE / ALIGNMENT];
static unsigned int avail = SPACE; /* multiple of ALIGNMENT; 0<=avail<=SPACE */

// /*@null@*//*@out@*/char *alloc(unsigned int n) -- old style
void *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(void *x) 
{
  if (x >= space)
    if (x < space + SPACE)
      return; /* XXX: assuming that pointers are flat */
  free(x);
}

int alloc_re(void **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;
}