/*
  l_mem.c - Routines for memory allocation in C.
  Samuel A. Rebelsky
  Version 0.1 of 3 March 2007
 */

#include <stdlib.h>
#include <stdio.h>
#include "l.h"

/* All of the available pairs.  (Kept in a known area of memory so that we can
 * clean up when necessary.)
 */
static struct pair *mem;

/* The index of the first free element. */
static int freemem;

/* The number of pairs available in memory. */
static int memsize;

/* Clean up memory to free space. */
static void
gc()
{
  /* STUB */
  fprintf(stderr, "Out of memory.  Exiting.\n");
  exit(1);
} /* gc() */

/* Set up the "memory" of the system to permit up to size dotted pairs. */
void
init_mem(int size)
{
  mem = (struct pair *) malloc(size * sizeof(struct pair));
  memsize = size;
  freemem = 0;
} /* init_mem() */

static pair
palloc()
{
  if (freemem >= memsize) {
    gc();
  }
  return mem + freemem++;
}

pair 
allocate_pair(pointer left, pointer right)
{
  pair result = palloc();
  CAR(result) = left;
  CDR(result) = right;
  return result;
} /* allocate_pair(pointer, pointer) */