Rudimentary storage allocator

#define ALLOCSIZE   1000     /*size of available space */
static char allocbuf[ALLOCSIZE];   /*storage for alloc */
static char *allocp = allocbuf;    /* next free position */

char *alloc(int n) /*return pointer to n characters */
{
   if (allocbuf + ALLOCSIZE -allocp >= n){   /* it fits */
      allocp += n;
      return allocp - n;   /*old p */
   }else   /*not enough room */
        return 0;
}
void afree(char *p)   /* free storage pointed to by p */
{
   if (p >= allocbuf && p <allocbuf + ALLOCSIZE)
       allocp = p;
}