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     MALLOC(3)                                               MALLOC(3)

          malloc, free, realloc, ialloc, calloc, cfree - main memory

          char *malloc(size)
          unsigned size;

          char *ptr;

          char *realloc(ptr, size)
          char *ptr;
          unsigned size;

          ialloc(ptr, size)
          char *ptr;
          unsigned size;

          char *calloc(nelem, elsize)
          unsigned nelem, elsize;

          char *ptr;

          Malloc and free provide a simple general-purpose memory
          allocation package.  Malloc returns a pointer to a new block
          of at least size bytes.

          The argument to free is a pointer to a block previously
          allocated by malloc; this space is made available for fur-
          ther allocation.  The present implementation of free does
          not change the contents; but it is unwise to depend on this

          Realloc changes the size of the block pointed to by ptr to
          size bytes and returns a pointer to the (possibly moved)
          block.  The contents will be unchanged up to the lesser of
          the new and old sizes.

          Ialloc inserts into the arena a designated block of store
          that was not previously known to the allocator.

          Calloc allocates space for an array of nelem elements of
          size elsize. The space is initialized to zeros.  Cfree frees
          such a block.

          Each of the allocation routines returns a pointer to space
          suitably aligned (after possible pointer coercion) for

     MALLOC(3)                                               MALLOC(3)

          storage of any type of object.

          The arena, though not necessarily contiguous, is kept in
          strict address order.  Malloc allocates the first big enough
          contiguous reach of free space found in a circular search
          from the last block allocated or freed, coalescing adjacent
          free blocks as it searches.  It calls sbrk (see break(2)) to
          get more memory from the system when there is no suitable
          space already free.  It has been arranged that realloc will
          work on a block that has been freed, provided no other allo-
          cations have intervened.  This questionable, unportable
          practice allows combinations of free, realloc and malloc to
          be used to rearrange the arena.

          galloc(3), sbrk(2)

          Malloc, realloc and calloc return a null pointer (0) if
          there is no available memory or if the arena has been
          detectably corrupted by storing outside the bounds of a
          block.  A very stringently checking version of malloc, which
          aborts with a diagnostic if the arena is corrupted, can be
          created by recompilation with a debugging flag set; see the

          When realloc returns 0, the block pointed to by ptr may be
          Malloc is general, not fast.  A program that repeatedly
          allocates and frees a particular kind of block often can be
          speeded up by superimposing a block-cacheing or suballoca-
          tion scheme on top of malloc-free.