/*
  malloc(size_t n)
  Returns a pointer to a newly allocated chunk of at least n bytes, or null
  if no space is available. Additionally, on failure, errno is
  set to ENOMEM on ANSI C systems.

  If n is zero, malloc returns a minumum-sized chunk. (The minimum
  size is 16 bytes on most 32bit systems, and 24 or 32 bytes on 64bit
  systems.)  On most systems, size_t is an unsigned type, so calls
  with negative arguments are interpreted as requests for huge amounts
  of space, which will often fail. The maximum supported value of n
  differs across systems, but is in all cases less than the maximum
  representable value of a size_t.
*/

/*
  free(void* p)
  Releases the chunk of memory pointed to by p, that had been previously
  allocated using malloc or a related routine such as realloc.
  It has no effect if p is null. It can have arbitrary (i.e., bad!)
  effects if p has already been freed.

  Unless disabled (using mallopt), freeing very large spaces will
  when possible, automatically trigger operations that give
  back unused memory to the system, thus reducing program footprint.
*/

/*
  This struct declaration is misleading (but accurate and necessary).
  It declares a "view" into memory allowing access to necessary
  fields at known offsets from a given base. See explanation below.
*/
struct malloc_chunk {

  INTERNAL_SIZE_T      prev_size;  /* Size of previous chunk (if free).  */
  INTERNAL_SIZE_T      size;       /* Size in bytes, including overhead. */

  struct malloc_chunk* fd;         /* double links -- used only if free. */
  struct malloc_chunk* bk;

  /* Only used for large blocks: pointer to next larger size.  */
  struct malloc_chunk* fd_nextsize; /* double links -- used only if free. */
  struct malloc_chunk* bk_nextsize;
};

/* INTERNAL_SIZE_T is the word-size used for internal bookkeeping of
   chunk sizes.
   The default version is the same as size_t.
   While not strictly necessary, it is best to define this as an
   unsigned type, even if size_t is a signed type. This may avoid some
   artificial size limitations on some systems.
   On a 64-bit machine, you may be able to reduce malloc overhead by
   defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' at the
   expense of not being able to handle more than 2^32 of malloced
   space. If this limitation is acceptable, you are encouraged to set
   this unless you are on a platform requiring 16byte alignments. In
   this case the alignment requirements turn out to negate any
   potential advantages of decreasing size_t word size.
   Implementors: Beware of the possible combinations of:
     - INTERNAL_SIZE_T might be signed or unsigned, might be 32 or 64 bits,
       and might be the same width as int or as long
     - size_t might have different width and signedness as INTERNAL_SIZE_T
     - int and long might be 32 or 64 bits, and might be the same width
   To deal with this, most comparisons and difference computations
   among INTERNAL_SIZE_Ts should cast them to unsigned long, being
   aware of the fact that casting an unsigned int to a wider long does
   not sign-extend. (This also makes checking for negative numbers
   awkward.) Some of these casts result in harmless compiler warnings
   on some systems.  */
#ifndef INTERNAL_SIZE_T
# define INTERNAL_SIZE_T size_t
#endif

/* The corresponding word size.  */
#define SIZE_SZ (sizeof (INTERNAL_SIZE_T))

/* The corresponding bit mask value.  */
#define MALLOC_ALIGN_MASK (MALLOC_ALIGNMENT - 1)