uclibc-ng/libc/stdlib/malloc-standard/malloc.h

/*
  This is a version (aka dlmalloc) of malloc/free/realloc written by
  Doug Lea and released to the public domain.  Use, modify, and
  redistribute this code without permission or acknowledgement in any
  way you wish.  Send questions, comments, complaints, performance
  data, etc to dl@cs.oswego.edu

  VERSION 2.7.2 Sat Aug 17 09:07:30 2002  Doug Lea  (dl at gee)

  Note: There may be an updated version of this malloc obtainable at
           ftp://gee.cs.oswego.edu/pub/misc/malloc.c
  Check before installing!

  Hacked up for uClibc by Erik Andersen <andersen@codepoet.org>
*/

#include <features.h>
#include <stddef.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <malloc.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <bits/uClibc_mutex.h>
#include <bits/uClibc_page.h>



__UCLIBC_MUTEX_EXTERN(__malloc_lock)
#if defined __UCLIBC_HAS_THREADS__ && !defined __UCLIBC_HAS_LINUXTHREADS__
	attribute_hidden
#endif
	;
#define __MALLOC_LOCK		__UCLIBC_MUTEX_LOCK(__malloc_lock)
#define __MALLOC_UNLOCK		__UCLIBC_MUTEX_UNLOCK(__malloc_lock)



/*
  MALLOC_ALIGNMENT is the minimum alignment for malloc'ed chunks.
  It must be a power of two at least 2 * (sizeof(size_t)), even on machines
  for which smaller alignments would suffice. It may be defined as
  larger than this though. Note however that code and data structures
  are optimized for the case of 8-byte alignment.
*/
#ifndef MALLOC_ALIGNMENT
#define MALLOC_ALIGNMENT       (2 * (sizeof(size_t)))
#endif

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

/*
  TRIM_FASTBINS controls whether free() of a very small chunk can
  immediately lead to trimming. Setting to true (1) can reduce memory
  footprint, but will almost always slow down programs that use a lot
  of small chunks.

  Define this only if you are willing to give up some speed to more
  aggressively reduce system-level memory footprint when releasing
  memory in programs that use many small chunks.  You can get
  essentially the same effect by setting MXFAST to 0, but this can
  lead to even greater slowdowns in programs using many small chunks.
  TRIM_FASTBINS is an in-between compile-time option, that disables
  only those chunks bordering topmost memory from being placed in
  fastbins.
*/
#ifndef TRIM_FASTBINS
#define TRIM_FASTBINS  0
#endif


/*
  MORECORE-related declarations. By default, rely on sbrk
*/


/*
  MORECORE is the name of the routine to call to obtain more memory
  from the system.  See below for general guidance on writing
  alternative MORECORE functions, as well as a version for WIN32 and a
  sample version for pre-OSX macos.
*/
#ifndef MORECORE
#define MORECORE sbrk
#endif

/*
  MORECORE_FAILURE is the value returned upon failure of MORECORE
  as well as mmap. Since it cannot be an otherwise valid memory address,
  and must reflect values of standard sys calls, you probably ought not
  try to redefine it.
*/
#ifndef MORECORE_FAILURE
#define MORECORE_FAILURE (-1)
#endif

/*
  If MORECORE_CONTIGUOUS is true, take advantage of fact that
  consecutive calls to MORECORE with positive arguments always return
  contiguous increasing addresses.  This is true of unix sbrk.  Even
  if not defined, when regions happen to be contiguous, malloc will
  permit allocations spanning regions obtained from different
  calls. But defining this when applicable enables some stronger
  consistency checks and space efficiencies.
*/
#ifndef MORECORE_CONTIGUOUS
#define MORECORE_CONTIGUOUS 1
#endif

/*
   MMAP_AS_MORECORE_SIZE is the minimum mmap size argument to use if
   sbrk fails, and mmap is used as a backup (which is done only if
   HAVE_MMAP).  The value must be a multiple of page size.  This
   backup strategy generally applies only when systems have "holes" in
   address space, so sbrk cannot perform contiguous expansion, but
   there is still space available on system.  On systems for which
   this is known to be useful (i.e. most linux kernels), this occurs
   only when programs allocate huge amounts of memory.  Between this,
   and the fact that mmap regions tend to be limited, the size should
   be large, to avoid too many mmap calls and thus avoid running out
   of kernel resources.
*/
#ifndef MMAP_AS_MORECORE_SIZE
#define MMAP_AS_MORECORE_SIZE (1024 * 1024)
#endif

/*
  The system page size. To the extent possible, this malloc manages
  memory from the system in page-size units.  Note that this value is
  cached during initialization into a field of malloc_state. So even
  if malloc_getpagesize is a function, it is only called once.

  The following mechanics for getpagesize were adapted from bsd/gnu
  getpagesize.h. If none of the system-probes here apply, a value of
  4096 is used, which should be OK: If they don't apply, then using
  the actual value probably doesn't impact performance.
*/
#ifndef malloc_getpagesize
#  include <unistd.h>
#  define malloc_getpagesize getpagesize()
#else /* just guess */
#  define malloc_getpagesize (4096)
#endif


/* mallopt tuning options */

/*
  M_MXFAST is the maximum request size used for "fastbins", special bins
  that hold returned chunks without consolidating their spaces. This
  enables future requests for chunks of the same size to be handled
  very quickly, but can increase fragmentation, and thus increase the
  overall memory footprint of a program.

  This malloc manages fastbins very conservatively yet still
  efficiently, so fragmentation is rarely a problem for values less
  than or equal to the default.  The maximum supported value of MXFAST
  is 80. You wouldn't want it any higher than this anyway.  Fastbins
  are designed especially for use with many small structs, objects or
  strings -- the default handles structs/objects/arrays with sizes up
  to 16 4byte fields, or small strings representing words, tokens,
  etc. Using fastbins for larger objects normally worsens
  fragmentation without improving speed.

  M_MXFAST is set in REQUEST size units. It is internally used in
  chunksize units, which adds padding and alignment.  You can reduce
  M_MXFAST to 0 to disable all use of fastbins.  This causes the malloc
  algorithm to be a closer approximation of fifo-best-fit in all cases,
  not just for larger requests, but will generally cause it to be
  slower.
*/


/* M_MXFAST is a standard SVID/XPG tuning option, usually listed in malloc.h */
#ifndef M_MXFAST
#define M_MXFAST            1
#endif

#ifndef DEFAULT_MXFAST
#define DEFAULT_MXFAST     64
#endif


/*
  M_TRIM_THRESHOLD is the maximum amount of unused top-most memory
  to keep before releasing via malloc_trim in free().

  Automatic trimming is mainly useful in long-lived programs.
  Because trimming via sbrk can be slow on some systems, and can
  sometimes be wasteful (in cases where programs immediately
  afterward allocate more large chunks) the value should be high
  enough so that your overall system performance would improve by
  releasing this much memory.

  The trim threshold and the mmap control parameters (see below)
  can be traded off with one another. Trimming and mmapping are
  two different ways of releasing unused memory back to the
  system. Between these two, it is often possible to keep
  system-level demands of a long-lived program down to a bare
  minimum. For example, in one test suite of sessions measuring
  the XF86 X server on Linux, using a trim threshold of 128K and a
  mmap threshold of 192K led to near-minimal long term resource
  consumption.

  If you are using this malloc in a long-lived program, it should
  pay to experiment with these values.  As a rough guide, you
  might set to a value close to the average size of a process
  (program) running on your system.  Releasing this much memory
  would allow such a process to run in memory.  Generally, it's
  worth it to tune for trimming rather tham memory mapping when a
  program undergoes phases where several large chunks are
  allocated and released in ways that can reuse each other's
  storage, perhaps mixed with phases where there are no such
  chunks at all.  And in well-behaved long-lived programs,
  controlling release of large blocks via trimming versus mapping
  is usually faster.

  However, in most programs, these parameters serve mainly as
  protection against the system-level effects of carrying around
  massive amounts of unneeded memory. Since frequent calls to
  sbrk, mmap, and munmap otherwise degrade performance, the default
  parameters are set to relatively high values that serve only as
  safeguards.

  The trim value must be greater than page size to have any useful
  effect.  To disable trimming completely, you can set to
  (unsigned long)(-1)

  Trim settings interact with fastbin (MXFAST) settings: Unless
  TRIM_FASTBINS is defined, automatic trimming never takes place upon
  freeing a chunk with size less than or equal to MXFAST. Trimming is
  instead delayed until subsequent freeing of larger chunks. However,
  you can still force an attempted trim by calling malloc_trim.

  Also, trimming is not generally possible in cases where
  the main arena is obtained via mmap.

  Note that the trick some people use of mallocing a huge space and
  then freeing it at program startup, in an attempt to reserve system
  memory, doesn't have the intended effect under automatic trimming,
  since that memory will immediately be returned to the system.
*/
#define M_TRIM_THRESHOLD       -1

#ifndef DEFAULT_TRIM_THRESHOLD
#define DEFAULT_TRIM_THRESHOLD (256 * 1024)
#endif

/*
  M_TOP_PAD is the amount of extra `padding' space to allocate or
  retain whenever sbrk is called. It is used in two ways internally:

  * When sbrk is called to extend the top of the arena to satisfy
  a new malloc request, this much padding is added to the sbrk
  request.

  * When malloc_trim is called automatically from free(),
  it is used as the `pad' argument.

  In both cases, the actual amount of padding is rounded
  so that the end of the arena is always a system page boundary.

  The main reason for using padding is to avoid calling sbrk so
  often. Having even a small pad greatly reduces the likelihood
  that nearly every malloc request during program start-up (or
  after trimming) will invoke sbrk, which needlessly wastes
  time.

  Automatic rounding-up to page-size units is normally sufficient
  to avoid measurable overhead, so the default is 0.  However, in
  systems where sbrk is relatively slow, it can pay to increase
  this value, at the expense of carrying around more memory than
  the program needs.
*/
#define M_TOP_PAD              -2

#ifndef DEFAULT_TOP_PAD
#define DEFAULT_TOP_PAD        (0)
#endif

/*
  M_MMAP_THRESHOLD is the request size threshold for using mmap()
  to service a request. Requests of at least this size that cannot
  be allocated using already-existing space will be serviced via mmap.
  (If enough normal freed space already exists it is used instead.)

  Using mmap segregates relatively large chunks of memory so that
  they can be individually obtained and released from the host
  system. A request serviced through mmap is never reused by any
  other request (at least not directly; the system may just so
  happen to remap successive requests to the same locations).

  Segregating space in this way has the benefits that:

   1. Mmapped space can ALWAYS be individually released back
      to the system, which helps keep the system level memory
      demands of a long-lived program low.
   2. Mapped memory can never become `locked' between
      other chunks, as can happen with normally allocated chunks, which
      means that even trimming via malloc_trim would not release them.
   3. On some systems with "holes" in address spaces, mmap can obtain
      memory that sbrk cannot.

  However, it has the disadvantages that:

   1. The space cannot be reclaimed, consolidated, and then
      used to service later requests, as happens with normal chunks.
   2. It can lead to more wastage because of mmap page alignment
      requirements
   3. It causes malloc performance to be more dependent on host
      system memory management support routines which may vary in
      implementation quality and may impose arbitrary
      limitations. Generally, servicing a request via normal
      malloc steps is faster than going through a system's mmap.

  The advantages of mmap nearly always outweigh disadvantages for
  "large" chunks, but the value of "large" varies across systems.  The
  default is an empirically derived value that works well in most
  systems.
*/
#define M_MMAP_THRESHOLD      -3

#ifndef DEFAULT_MMAP_THRESHOLD
#define DEFAULT_MMAP_THRESHOLD (256 * 1024)
#endif

/*
  M_MMAP_MAX is the maximum number of requests to simultaneously
  service using mmap. This parameter exists because
. Some systems have a limited number of internal tables for
  use by mmap, and using more than a few of them may degrade
  performance.

  The default is set to a value that serves only as a safeguard.
  Setting to 0 disables use of mmap for servicing large requests.  If
  HAVE_MMAP is not set, the default value is 0, and attempts to set it
  to non-zero values in mallopt will fail.
*/
#define M_MMAP_MAX             -4

#ifndef DEFAULT_MMAP_MAX
#define DEFAULT_MMAP_MAX       (65536)
#endif


/* ------------------ MMAP support ------------------  */
#include <fcntl.h>
#include <sys/mman.h>

#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
#define MAP_ANONYMOUS MAP_ANON
#endif

#ifdef __ARCH_USE_MMU__
# define _MAP_UNINITIALIZED 0
#else
# define _MAP_UNINITIALIZED MAP_UNINITIALIZED
#endif

#define MMAP(addr, size, prot) \
 (mmap((addr), (size), (prot), MAP_PRIVATE|MAP_ANONYMOUS|_MAP_UNINITIALIZED, 0, 0))


/* -----------------------  Chunk representations ----------------------- */


/*
  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 {

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

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


typedef struct malloc_chunk* mchunkptr;

/*
   malloc_chunk details:

    (The following includes lightly edited explanations by Colin Plumb.)

    Chunks of memory are maintained using a `boundary tag' method as
    described in e.g., Knuth or Standish.  (See the paper by Paul
    Wilson ftp://ftp.cs.utexas.edu/pub/garbage/allocsrv.ps for a
    survey of such techniques.)  Sizes of free chunks are stored both
    in the front of each chunk and at the end.  This makes
    consolidating fragmented chunks into bigger chunks very fast.  The
    size fields also hold bits representing whether chunks are free or
    in use.

    An allocated chunk looks like this:


    chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Size of previous chunk, if allocated            | |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Size of chunk, in bytes                         |P|
      mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             User data starts here...                          .
            .                                                               .
            .             (malloc_usable_space() bytes)                     .
            .                                                               |
nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Size of chunk                                     |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Where "chunk" is the front of the chunk for the purpose of most of
    the malloc code, but "mem" is the pointer that is returned to the
    user.  "Nextchunk" is the beginning of the next contiguous chunk.

    Chunks always begin on even word boundries, so the mem portion
    (which is returned to the user) is also on an even word boundary, and
    thus at least double-word aligned.

    Free chunks are stored in circular doubly-linked lists, and look like this:

    chunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Size of previous chunk                            |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    `head:' |             Size of chunk, in bytes                         |P|
      mem-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Forward pointer to next chunk in list             |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Back pointer to previous chunk in list            |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |             Unused space (may be 0 bytes long)                .
            .                                                               .
            .                                                               |
nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    `foot:' |             Size of chunk, in bytes                           |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The P (PREV_INUSE) bit, stored in the unused low-order bit of the
    chunk size (which is always a multiple of two words), is an in-use
    bit for the *previous* chunk.  If that bit is *clear*, then the
    word before the current chunk size contains the previous chunk
    size, and can be used to find the front of the previous chunk.
    The very first chunk allocated always has this bit set,
    preventing access to non-existent (or non-owned) memory. If
    prev_inuse is set for any given chunk, then you CANNOT determine
    the size of the previous chunk, and might even get a memory
    addressing fault when trying to do so.

    Note that the `foot' of the current chunk is actually represented
    as the prev_size of the NEXT chunk. This makes it easier to
    deal with alignments etc but can be very confusing when trying
    to extend or adapt this code.

    The two exceptions to all this are

     1. The special chunk `top' doesn't bother using the
        trailing size field since there is no next contiguous chunk
        that would have to index off it. After initialization, `top'
        is forced to always exist.  If it would become less than
        MINSIZE bytes long, it is replenished.

     2. Chunks allocated via mmap, which have the second-lowest-order
        bit (IS_MMAPPED) set in their size fields.  Because they are
        allocated one-by-one, each must contain its own trailing size field.

*/

/*
  ---------- Size and alignment checks and conversions ----------
*/

/* conversion from malloc headers to user pointers, and back */

#define chunk2mem(p)   ((void*)((char*)(p) + 2*(sizeof(size_t))))
#define mem2chunk(mem) ((mchunkptr)((char*)(mem) - 2*(sizeof(size_t))))

/* The smallest possible chunk */
#define MIN_CHUNK_SIZE        (sizeof(struct malloc_chunk))

/* The smallest size we can malloc is an aligned minimal chunk */

#define MINSIZE  \
  (unsigned long)(((MIN_CHUNK_SIZE+MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK))

/* Check if m has acceptable alignment */

#define aligned_OK(m)  (((unsigned long)((m)) & (MALLOC_ALIGN_MASK)) == 0)


/* Check if a request is so large that it would wrap around zero when
   padded and aligned. To simplify some other code, the bound is made
   low enough so that adding MINSIZE will also not wrap around sero.
*/

#define REQUEST_OUT_OF_RANGE(req)                                 \
  ((unsigned long)(req) >=                                        \
   (unsigned long)(size_t)(-2 * MINSIZE))

/* pad request bytes into a usable size -- internal version */

#define request2size(req)                                         \
  (((req) + (sizeof(size_t)) + MALLOC_ALIGN_MASK < MINSIZE)  ?             \
   MINSIZE :                                                      \
   ((req) + (sizeof(size_t)) + MALLOC_ALIGN_MASK) & ~MALLOC_ALIGN_MASK)

/*  Same, except also perform argument check */

#define checked_request2size(req, sz)                             \
  if (REQUEST_OUT_OF_RANGE(req)) {                                \
    __set_errno(ENOMEM);                                          \
    return 0;                                                     \
  }                                                               \
  (sz) = request2size(req);

/*
  --------------- Physical chunk operations ---------------
*/


/* size field is or'ed with PREV_INUSE when previous adjacent chunk in use */
#define PREV_INUSE 0x1

/* extract inuse bit of previous chunk */
#define prev_inuse(p)       ((p)->size & PREV_INUSE)


/* size field is or'ed with IS_MMAPPED if the chunk was obtained with mmap() */
#define IS_MMAPPED 0x2

/* check for mmap()'ed chunk */
#define chunk_is_mmapped(p) ((p)->size & IS_MMAPPED)

/* Bits to mask off when extracting size

  Note: IS_MMAPPED is intentionally not masked off from size field in
  macros for which mmapped chunks should never be seen. This should
  cause helpful core dumps to occur if it is tried by accident by
  people extending or adapting this malloc.
*/
#define SIZE_BITS (PREV_INUSE|IS_MMAPPED)

/* Get size, ignoring use bits */
#define chunksize(p)         ((p)->size & ~(SIZE_BITS))


/* Ptr to next physical malloc_chunk. */
#define next_chunk(p) ((mchunkptr)( ((char*)(p)) + ((p)->size & ~PREV_INUSE) ))

/* Ptr to previous physical malloc_chunk */
#define prev_chunk(p) ((mchunkptr)( ((char*)(p)) - ((p)->prev_size) ))

/* Treat space at ptr + offset as a chunk */
#define chunk_at_offset(p, s)  ((mchunkptr)(((char*)(p)) + (s)))

/* extract p's inuse bit */
#define inuse(p)\
((((mchunkptr)(((char*)(p))+((p)->size & ~PREV_INUSE)))->size) & PREV_INUSE)

/* set/clear chunk as being inuse without otherwise disturbing */
#define set_inuse(p)\
((mchunkptr)(((char*)(p)) + ((p)->size & ~PREV_INUSE)))->size |= PREV_INUSE

#define clear_inuse(p)\
((mchunkptr)(((char*)(p)) + ((p)->size & ~PREV_INUSE)))->size &= ~(PREV_INUSE)


/* check/set/clear inuse bits in known places */
#define inuse_bit_at_offset(p, s)\
 (((mchunkptr)(((char*)(p)) + (s)))->size & PREV_INUSE)

#define set_inuse_bit_at_offset(p, s)\
 (((mchunkptr)(((char*)(p)) + (s)))->size |= PREV_INUSE)

#define clear_inuse_bit_at_offset(p, s)\
 (((mchunkptr)(((char*)(p)) + (s)))->size &= ~(PREV_INUSE))


/* Set size at head, without disturbing its use bit */
#define set_head_size(p, s)  ((p)->size = (((p)->size & PREV_INUSE) | (s)))

/* Set size/use field */
#define set_head(p, s)       ((p)->size = (s))

/* Set size at footer (only when chunk is not in use) */
#define set_foot(p, s)       (((mchunkptr)((char*)(p) + (s)))->prev_size = (s))


/* -------------------- Internal data structures -------------------- */

/*
  Bins

    An array of bin headers for free chunks. Each bin is doubly
    linked.  The bins are approximately proportionally (log) spaced.
    There are a lot of these bins (128). This may look excessive, but
    works very well in practice.  Most bins hold sizes that are
    unusual as malloc request sizes, but are more usual for fragments
    and consolidated sets of chunks, which is what these bins hold, so
    they can be found quickly.  All procedures maintain the invariant
    that no consolidated chunk physically borders another one, so each
    chunk in a list is known to be preceeded and followed by either
    inuse chunks or the ends of memory.

    Chunks in bins are kept in size order, with ties going to the
    approximately least recently used chunk. Ordering isn't needed
    for the small bins, which all contain the same-sized chunks, but
    facilitates best-fit allocation for larger chunks. These lists
    are just sequential. Keeping them in order almost never requires
    enough traversal to warrant using fancier ordered data
    structures.

    Chunks of the same size are linked with the most
    recently freed at the front, and allocations are taken from the
    back.  This results in LRU (FIFO) allocation order, which tends
    to give each chunk an equal opportunity to be consolidated with
    adjacent freed chunks, resulting in larger free chunks and less
    fragmentation.

    To simplify use in double-linked lists, each bin header acts
    as a malloc_chunk. This avoids special-casing for headers.
    But to conserve space and improve locality, we allocate
    only the fd/bk pointers of bins, and then use repositioning tricks
    to treat these as the fields of a malloc_chunk*.
*/

typedef struct malloc_chunk* mbinptr;

/* addressing -- note that bin_at(0) does not exist */
#define bin_at(m, i) ((mbinptr)((char*)&((m)->bins[(i)<<1]) - ((sizeof(size_t))<<1)))

/* analog of ++bin */
#define next_bin(b)  ((mbinptr)((char*)(b) + (sizeof(mchunkptr)<<1)))

/* Reminders about list directionality within bins */
#define first(b)     ((b)->fd)
#define last(b)      ((b)->bk)

/* Take a chunk off a bin list */
#define unlink(P, BK, FD) {                                            \
  FD = P->fd;                                                          \
  BK = P->bk;                                                          \
  if (FD->bk != P || BK->fd != P)                                      \
      abort();                                                         \
  FD->bk = BK;                                                         \
  BK->fd = FD;                                                         \
}

/*
  Indexing

    Bins for sizes < 512 bytes contain chunks of all the same size, spaced
    8 bytes apart. Larger bins are approximately logarithmically spaced:

    64 bins of size       8
    32 bins of size      64
    16 bins of size     512
     8 bins of size    4096
     4 bins of size   32768
     2 bins of size  262144
     1 bin  of size what's left

    The bins top out around 1MB because we expect to service large
    requests via mmap.
*/

#define NBINS              96
#define NSMALLBINS         32
#define SMALLBIN_WIDTH      8
#define MIN_LARGE_SIZE    256

#define in_smallbin_range(sz)  \
  ((unsigned long)(sz) < (unsigned long)MIN_LARGE_SIZE)

#define smallbin_index(sz)     (((unsigned)(sz)) >> 3)

#define bin_index(sz) \
 ((in_smallbin_range(sz)) ? smallbin_index(sz) : __malloc_largebin_index(sz))

/*
  FIRST_SORTED_BIN_SIZE is the chunk size corresponding to the
  first bin that is maintained in sorted order. This must
  be the smallest size corresponding to a given bin.

  Normally, this should be MIN_LARGE_SIZE. But you can weaken
  best fit guarantees to sometimes speed up malloc by increasing value.
  Doing this means that malloc may choose a chunk that is
  non-best-fitting by up to the width of the bin.

  Some useful cutoff values:
      512 - all bins sorted
     2560 - leaves bins <=     64 bytes wide unsorted
    12288 - leaves bins <=    512 bytes wide unsorted
    65536 - leaves bins <=   4096 bytes wide unsorted
   262144 - leaves bins <=  32768 bytes wide unsorted
       -1 - no bins sorted (not recommended!)
*/

#define FIRST_SORTED_BIN_SIZE MIN_LARGE_SIZE
/* #define FIRST_SORTED_BIN_SIZE 65536 */

/*
  Unsorted chunks

    All remainders from chunk splits, as well as all returned chunks,
    are first placed in the "unsorted" bin. They are then placed
    in regular bins after malloc gives them ONE chance to be used before
    binning. So, basically, the unsorted_chunks list acts as a queue,
    with chunks being placed on it in free (and __malloc_consolidate),
    and taken off (to be either used or placed in bins) in malloc.
*/

/* The otherwise unindexable 1-bin is used to hold unsorted chunks. */
#define unsorted_chunks(M)          (bin_at(M, 1))

/*
  Top

    The top-most available chunk (i.e., the one bordering the end of
    available memory) is treated specially. It is never included in
    any bin, is used only if no other chunk is available, and is
    released back to the system if it is very large (see
    M_TRIM_THRESHOLD).  Because top initially
    points to its own bin with initial zero size, thus forcing
    extension on the first malloc request, we avoid having any special
    code in malloc to check whether it even exists yet. But we still
    need to do so when getting memory from system, so we make
    initial_top treat the bin as a legal but unusable chunk during the
    interval between initialization and the first call to
    __malloc_alloc. (This is somewhat delicate, since it relies on
    the 2 preceding words to be zero during this interval as well.)
*/

/* Conveniently, the unsorted bin can be used as dummy top on first call */
#define initial_top(M)              (unsorted_chunks(M))

/*
  Binmap

    To help compensate for the large number of bins, a one-level index
    structure is used for bin-by-bin searching.  `binmap' is a
    bitvector recording whether bins are definitely empty so they can
    be skipped over during during traversals.  The bits are NOT always
    cleared as soon as bins are empty, but instead only
    when they are noticed to be empty during traversal in malloc.
*/

/* Conservatively use 32 bits per map word, even if on 64bit system */
#define BINMAPSHIFT      5
#define BITSPERMAP       (1U << BINMAPSHIFT)
#define BINMAPSIZE       (NBINS / BITSPERMAP)

#define idx2block(i)     ((i) >> BINMAPSHIFT)
#define idx2bit(i)       ((1U << ((i) & ((1U << BINMAPSHIFT)-1))))

#define mark_bin(m,i)    ((m)->binmap[idx2block(i)] |=  idx2bit(i))
#define unmark_bin(m,i)  ((m)->binmap[idx2block(i)] &= ~(idx2bit(i)))
#define get_binmap(m,i)  ((m)->binmap[idx2block(i)] &   idx2bit(i))

/*
  Fastbins

    An array of lists holding recently freed small chunks.  Fastbins
    are not doubly linked.  It is faster to single-link them, and
    since chunks are never removed from the middles of these lists,
    double linking is not necessary. Also, unlike regular bins, they
    are not even processed in FIFO order (they use faster LIFO) since
    ordering doesn't much matter in the transient contexts in which
    fastbins are normally used.

    Chunks in fastbins keep their inuse bit set, so they cannot
    be consolidated with other free chunks. __malloc_consolidate
    releases all chunks in fastbins and consolidates them with
    other free chunks.
*/

typedef struct malloc_chunk* mfastbinptr;

/* offset 2 to use otherwise unindexable first 2 bins */
#define fastbin_index(sz)        ((((unsigned int)(sz)) >> 3) - 2)

/* The maximum fastbin request size we support */
#define MAX_FAST_SIZE     80

#define NFASTBINS  (fastbin_index(request2size(MAX_FAST_SIZE))+1)

/*
  FASTBIN_CONSOLIDATION_THRESHOLD is the size of a chunk in free()
  that triggers automatic consolidation of possibly-surrounding
  fastbin chunks. This is a heuristic, so the exact value should not
  matter too much. It is defined at half the default trim threshold as a
  compromise heuristic to only attempt consolidation if it is likely
  to lead to trimming. However, it is not dynamically tunable, since
  consolidation reduces fragmentation surrounding loarge chunks even
  if trimming is not used.
*/

#define FASTBIN_CONSOLIDATION_THRESHOLD  \
  ((unsigned long)(DEFAULT_TRIM_THRESHOLD) >> 1)

/*
  Since the lowest 2 bits in max_fast don't matter in size comparisons,
  they are used as flags.
*/

/*
  ANYCHUNKS_BIT held in max_fast indicates that there may be any
  freed chunks at all. It is set true when entering a chunk into any
  bin.
*/

#define ANYCHUNKS_BIT        (1U)

#define have_anychunks(M)     (((M)->max_fast &  ANYCHUNKS_BIT))
#define set_anychunks(M)      ((M)->max_fast |=  ANYCHUNKS_BIT)
#define clear_anychunks(M)    ((M)->max_fast &= ~ANYCHUNKS_BIT)

/*
  FASTCHUNKS_BIT held in max_fast indicates that there are probably
  some fastbin chunks. It is set true on entering a chunk into any
  fastbin, and cleared only in __malloc_consolidate.
*/

#define FASTCHUNKS_BIT        (2U)

#define have_fastchunks(M)   (((M)->max_fast &  FASTCHUNKS_BIT))
#define set_fastchunks(M)    ((M)->max_fast |=  (FASTCHUNKS_BIT|ANYCHUNKS_BIT))
#define clear_fastchunks(M)  ((M)->max_fast &= ~(FASTCHUNKS_BIT))

/* Set value of max_fast.  Use impossibly small value if 0.  */
#define set_max_fast(M, s) \
  (M)->max_fast = (((s) == 0)? SMALLBIN_WIDTH: request2size(s)) | \
  ((M)->max_fast &  (FASTCHUNKS_BIT|ANYCHUNKS_BIT))

#define get_max_fast(M) \
  ((M)->max_fast & ~(FASTCHUNKS_BIT | ANYCHUNKS_BIT))

/*
  Safe-Linking:
  Use randomness from ASLR (mmap_base) to protect single-linked lists
  of fastbins. Together with allocation alignment checks, this mechanism
  reduces the risk of pointer hijacking, as was done with Safe-Unlinking
  in the double-linked lists of smallbins.
*/
#define PROTECT_PTR(pos, ptr)     ((mchunkptr)((((size_t)pos) >> PAGE_SHIFT) ^ ((size_t)ptr)))
#define REVEAL_PTR(pos, ptr)      PROTECT_PTR(pos, ptr)
#define PTR_FOR_ALIGNMENT_CHECK(P) \
    (MALLOC_ALIGNMENT == 2*(sizeof(size_t)) ? (P) : chunk2mem(P))

#define CHECK_PTR(P)                            \
  if (!aligned_OK(PTR_FOR_ALIGNMENT_CHECK(P)))  \
      abort();

/*
  morecore_properties is a status word holding dynamically discovered
  or controlled properties of the morecore function
*/

#define MORECORE_CONTIGUOUS_BIT  (1U)

#define contiguous(M) \
        (((M)->morecore_properties &  MORECORE_CONTIGUOUS_BIT))
#define noncontiguous(M) \
        (((M)->morecore_properties &  MORECORE_CONTIGUOUS_BIT) == 0)
#define set_contiguous(M) \
        ((M)->morecore_properties |=  MORECORE_CONTIGUOUS_BIT)
#define set_noncontiguous(M) \
        ((M)->morecore_properties &= ~MORECORE_CONTIGUOUS_BIT)


/*
   ----------- Internal state representation and initialization -----------
*/

struct malloc_state {

  /* The maximum chunk size to be eligible for fastbin */
  size_t  max_fast;   /* low 2 bits used as flags */

  /* Fastbins */
  mfastbinptr      fastbins[NFASTBINS];

  /* Base of the topmost chunk -- not otherwise kept in a bin */
  mchunkptr        top;

  /* The remainder from the most recent split of a small request */
  mchunkptr        last_remainder;

  /* Normal bins packed as described above */
  mchunkptr        bins[NBINS * 2];

  /* Bitmap of bins. Trailing zero map handles cases of largest binned size */
  unsigned int     binmap[BINMAPSIZE+1];

  /* Tunable parameters */
  unsigned long     trim_threshold;
  size_t  top_pad;
  size_t  mmap_threshold;

  /* Memory map support */
  int              n_mmaps;
  int              n_mmaps_max;
  int              max_n_mmaps;

  /* Cache malloc_getpagesize */
  unsigned int     pagesize;

  /* Track properties of MORECORE */
  unsigned int     morecore_properties;

  /* Statistics */
  size_t  mmapped_mem;
  size_t  sbrked_mem;
  size_t  max_sbrked_mem;
  size_t  max_mmapped_mem;
  size_t  max_total_mem;
};

typedef struct malloc_state *mstate;

/*
   There is exactly one instance of this struct in this malloc.
   If you are adapting this malloc in a way that does NOT use a static
   malloc_state, you MUST explicitly zero-fill it before using. This
   malloc relies on the property that malloc_state is initialized to
   all zeroes (as is true of C statics).
*/
extern struct malloc_state __malloc_state attribute_hidden;  /* never directly referenced */

/*
   All uses of av_ are via get_malloc_state().
   At most one "call" to get_malloc_state is made per invocation of
   the public versions of malloc and free, but other routines
   that in turn invoke malloc and/or free may call more then once.
   Also, it is called in check* routines if __UCLIBC_MALLOC_DEBUGGING__ is set.
*/

#define get_malloc_state() (&(__malloc_state))

/* External internal utilities operating on mstates */
void   __malloc_consolidate(mstate) attribute_hidden;


/* Debugging support */
#ifndef __UCLIBC_MALLOC_DEBUGGING__

#define check_chunk(P)
#define check_free_chunk(P)
#define check_inuse_chunk(P)
#define check_remalloced_chunk(P,N)
#define check_malloced_chunk(P,N)
#define check_malloc_state()
#define assert(x) ((void)0)


#else

#define check_chunk(P)              __do_check_chunk(P)
#define check_free_chunk(P)         __do_check_free_chunk(P)
#define check_inuse_chunk(P)        __do_check_inuse_chunk(P)
#define check_remalloced_chunk(P,N) __do_check_remalloced_chunk(P,N)
#define check_malloced_chunk(P,N)   __do_check_malloced_chunk(P,N)
#define check_malloc_state()        __do_check_malloc_state()

extern void __do_check_chunk(mchunkptr p) attribute_hidden;
extern void __do_check_free_chunk(mchunkptr p) attribute_hidden;
extern void __do_check_inuse_chunk(mchunkptr p) attribute_hidden;
extern void __do_check_remalloced_chunk(mchunkptr p, size_t s) attribute_hidden;
extern void __do_check_malloced_chunk(mchunkptr p, size_t s) attribute_hidden;
extern void __do_check_malloc_state(void) attribute_hidden;

#include <assert.h>

#endif