lib/luajit/src/lj_alloc.c

/*
** Bundled memory allocator.
**
** Beware: this is a HEAVILY CUSTOMIZED version of dlmalloc.
** The original bears the following remark:
**
**   This is a version (aka dlmalloc) of malloc/free/realloc written by
**   Doug Lea and released to the public domain, as explained at
**   http://creativecommons.org/licenses/publicdomain.
**
**   * Version pre-2.8.4 Wed Mar 29 19:46:29 2006    (dl at gee)
**
** No additional copyright is claimed over the customizations.
** Please do NOT bother the original author about this version here!
**
** If you want to use dlmalloc in another project, you should get
** the original from: ftp://gee.cs.oswego.edu/pub/misc/
** For thread-safe derivatives, take a look at:
** - ptmalloc: http://www.malloc.de/
** - nedmalloc: http://www.nedprod.com/programs/portable/nedmalloc/
*/

#define lj_alloc_c
#define LUA_CORE

/* To get the mremap prototype. Must be defined before any system includes. */
#if defined(__linux__) && !defined(_GNU_SOURCE)
#define _GNU_SOURCE
#endif

#include "lj_def.h"
#include "lj_arch.h"
#include "lj_alloc.h"

#ifndef LUAJIT_USE_SYSMALLOC

#define MAX_SIZE_T		(~(size_t)0)
#define MALLOC_ALIGNMENT	((size_t)8U)

#define DEFAULT_GRANULARITY	((size_t)128U * (size_t)1024U)
#define DEFAULT_TRIM_THRESHOLD	((size_t)2U * (size_t)1024U * (size_t)1024U)
#define DEFAULT_MMAP_THRESHOLD	((size_t)128U * (size_t)1024U)
#define MAX_RELEASE_CHECK_RATE	255

/* ------------------- size_t and alignment properties -------------------- */

/* The byte and bit size of a size_t */
#define SIZE_T_SIZE		(sizeof(size_t))
#define SIZE_T_BITSIZE		(sizeof(size_t) << 3)

/* Some constants coerced to size_t */
/* Annoying but necessary to avoid errors on some platforms */
#define SIZE_T_ZERO		((size_t)0)
#define SIZE_T_ONE		((size_t)1)
#define SIZE_T_TWO		((size_t)2)
#define TWO_SIZE_T_SIZES	(SIZE_T_SIZE<<1)
#define FOUR_SIZE_T_SIZES	(SIZE_T_SIZE<<2)
#define SIX_SIZE_T_SIZES	(FOUR_SIZE_T_SIZES+TWO_SIZE_T_SIZES)

/* The bit mask value corresponding to MALLOC_ALIGNMENT */
#define CHUNK_ALIGN_MASK	(MALLOC_ALIGNMENT - SIZE_T_ONE)

/* the number of bytes to offset an address to align it */
#define align_offset(A)\
 ((((size_t)(A) & CHUNK_ALIGN_MASK) == 0)? 0 :\
  ((MALLOC_ALIGNMENT - ((size_t)(A) & CHUNK_ALIGN_MASK)) & CHUNK_ALIGN_MASK))

/* -------------------------- MMAP support ------------------------------- */

#define MFAIL			((void *)(MAX_SIZE_T))
#define CMFAIL			((char *)(MFAIL)) /* defined for convenience */

#define IS_DIRECT_BIT		(SIZE_T_ONE)

#if LJ_TARGET_WINDOWS

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

#if LJ_64

/* Undocumented, but hey, that's what we all love so much about Windows. */
typedef long (*PNTAVM)(HANDLE handle, void **addr, ULONG zbits,
		       size_t *size, ULONG alloctype, ULONG prot);
static PNTAVM ntavm;

/* Number of top bits of the lower 32 bits of an address that must be zero.
** Apparently 0 gives us full 64 bit addresses and 1 gives us the lower 2GB.
*/
#define NTAVM_ZEROBITS		1

static void INIT_MMAP(void)
{
  ntavm = (PNTAVM)GetProcAddress(GetModuleHandleA("ntdll.dll"),
				 "NtAllocateVirtualMemory");
}

/* Win64 32 bit MMAP via NtAllocateVirtualMemory. */
static LJ_AINLINE void *CALL_MMAP(size_t size)
{
  DWORD olderr = GetLastError();
  void *ptr = NULL;
  long st = ntavm(INVALID_HANDLE_VALUE, &ptr, NTAVM_ZEROBITS, &size,
		  MEM_RESERVE|MEM_COMMIT, PAGE_READWRITE);
  SetLastError(olderr);
  return st == 0 ? ptr : MFAIL;
}

/* For direct MMAP, use MEM_TOP_DOWN to minimize interference */
static LJ_AINLINE void *DIRECT_MMAP(size_t size)
{
  DWORD olderr = GetLastError();
  void *ptr = NULL;
  long st = ntavm(INVALID_HANDLE_VALUE, &ptr, NTAVM_ZEROBITS, &size,
		  MEM_RESERVE|MEM_COMMIT|MEM_TOP_DOWN, PAGE_READWRITE);
  SetLastError(olderr);
  return st == 0 ? ptr : MFAIL;
}

#else

#define INIT_MMAP()		((void)0)

/* Win32 MMAP via VirtualAlloc */
static LJ_AINLINE void *CALL_MMAP(size_t size)
{
  DWORD olderr = GetLastError();
  void *ptr = VirtualAlloc(0, size, MEM_RESERVE|MEM_COMMIT, PAGE_READWRITE);
  SetLastError(olderr);
  return ptr ? ptr : MFAIL;
}

/* For direct MMAP, use MEM_TOP_DOWN to minimize interference */
static LJ_AINLINE void *DIRECT_MMAP(size_t size)
{
  DWORD olderr = GetLastError();
  void *ptr = VirtualAlloc(0, size, MEM_RESERVE|MEM_COMMIT|MEM_TOP_DOWN,
			   PAGE_READWRITE);
  SetLastError(olderr);
  return ptr ? ptr : MFAIL;
}

#endif

/* This function supports releasing coalesed segments */
static LJ_AINLINE int CALL_MUNMAP(void *ptr, size_t size)
{
  DWORD olderr = GetLastError();
  MEMORY_BASIC_INFORMATION minfo;
  char *cptr = (char *)ptr;
  while (size) {
    if (VirtualQuery(cptr, &minfo, sizeof(minfo)) == 0)
      return -1;
    if (minfo.BaseAddress != cptr || minfo.AllocationBase != cptr ||
	minfo.State != MEM_COMMIT || minfo.RegionSize > size)
      return -1;
    if (VirtualFree(cptr, 0, MEM_RELEASE) == 0)
      return -1;
    cptr += minfo.RegionSize;
    size -= minfo.RegionSize;
  }
  SetLastError(olderr);
  return 0;
}

#else

#include <errno.h>
#include <sys/mman.h>

#define MMAP_PROT		(PROT_READ|PROT_WRITE)
#if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
#define MAP_ANONYMOUS		MAP_ANON
#endif
#define MMAP_FLAGS		(MAP_PRIVATE|MAP_ANONYMOUS)

#if LJ_64
/* 64 bit mode needs special support for allocating memory in the lower 2GB. */

#if defined(MAP_32BIT)

#if defined(__sun__)
#define MMAP_REGION_START	((uintptr_t)0x1000)
#else
/* Actually this only gives us max. 1GB in current Linux kernels. */
#define MMAP_REGION_START	((uintptr_t)0)
#endif

static LJ_AINLINE void *CALL_MMAP(size_t size)
{
  int olderr = errno;
  void *ptr = mmap((void *)MMAP_REGION_START, size, MMAP_PROT, MAP_32BIT|MMAP_FLAGS, -1, 0);
  errno = olderr;
  return ptr;
}

#elif LJ_TARGET_OSX || LJ_TARGET_PS4 || defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) || defined(__sun__)

/* OSX and FreeBSD mmap() use a naive first-fit linear search.
** That's perfect for us. Except that -pagezero_size must be set for OSX,
** otherwise the lower 4GB are blocked. And the 32GB RLIMIT_DATA needs
** to be reduced to 250MB on FreeBSD.
*/
#if LJ_TARGET_OSX || defined(__DragonFly__)
#define MMAP_REGION_START	((uintptr_t)0x10000)
#elif LJ_TARGET_PS4
#define MMAP_REGION_START	((uintptr_t)0x4000)
#else
#define MMAP_REGION_START	((uintptr_t)0x10000000)
#endif
#define MMAP_REGION_END		((uintptr_t)0x80000000)

#if (defined(__FreeBSD__) || defined(__FreeBSD_kernel__)) && !LJ_TARGET_PS4
#include <sys/resource.h>
#endif

static LJ_AINLINE void *CALL_MMAP(size_t size)
{
  int olderr = errno;
  /* Hint for next allocation. Doesn't need to be thread-safe. */
  static uintptr_t alloc_hint = MMAP_REGION_START;
  int retry = 0;
#if (defined(__FreeBSD__) || defined(__FreeBSD_kernel__)) && !LJ_TARGET_PS4
  static int rlimit_modified = 0;
  if (LJ_UNLIKELY(rlimit_modified == 0)) {
    struct rlimit rlim;
    rlim.rlim_cur = rlim.rlim_max = MMAP_REGION_START;
    setrlimit(RLIMIT_DATA, &rlim);  /* Ignore result. May fail below. */
    rlimit_modified = 1;
  }
#endif
  for (;;) {
    void *p = mmap((void *)alloc_hint, size, MMAP_PROT, MMAP_FLAGS, -1, 0);
    if ((uintptr_t)p >= MMAP_REGION_START &&
	(uintptr_t)p + size < MMAP_REGION_END) {
      alloc_hint = (uintptr_t)p + size;
      errno = olderr;
      return p;
    }
    if (p != CMFAIL) munmap(p, size);
#if defined(__sun__) || defined(__DragonFly__)
    alloc_hint += 0x1000000;  /* Need near-exhaustive linear scan. */
    if (alloc_hint + size < MMAP_REGION_END) continue;
#endif
    if (retry) break;
    retry = 1;
    alloc_hint = MMAP_REGION_START;
  }
  errno = olderr;
  return CMFAIL;
}

#else

#error "NYI: need an equivalent of MAP_32BIT for this 64 bit OS"

#endif

#else

/* 32 bit mode is easy. */
static LJ_AINLINE void *CALL_MMAP(size_t size)
{
  int olderr = errno;
  void *ptr = mmap(NULL, size, MMAP_PROT, MMAP_FLAGS, -1, 0);
  errno = olderr;
  return ptr;
}

#endif

#define INIT_MMAP()		((void)0)
#define DIRECT_MMAP(s)		CALL_MMAP(s)

static LJ_AINLINE int CALL_MUNMAP(void *ptr, size_t size)
{
  int olderr = errno;
  int ret = munmap(ptr, size);
  errno = olderr;
  return ret;
}

#if LJ_TARGET_LINUX
/* Need to define _GNU_SOURCE to get the mremap prototype. */
static LJ_AINLINE void *CALL_MREMAP_(void *ptr, size_t osz, size_t nsz,
				     int flags)
{
  int olderr = errno;
  ptr = mremap(ptr, osz, nsz, flags);
  errno = olderr;
  return ptr;
}

#define CALL_MREMAP(addr, osz, nsz, mv) CALL_MREMAP_((addr), (osz), (nsz), (mv))
#define CALL_MREMAP_NOMOVE	0
#define CALL_MREMAP_MAYMOVE	1
#if LJ_64
#define CALL_MREMAP_MV		CALL_MREMAP_NOMOVE
#else
#define CALL_MREMAP_MV		CALL_MREMAP_MAYMOVE
#endif
#endif

#endif

#ifndef CALL_MREMAP
#define CALL_MREMAP(addr, osz, nsz, mv) ((void)osz, MFAIL)
#endif

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

struct malloc_chunk {
  size_t               prev_foot;  /* Size of previous chunk (if free).  */
  size_t               head;       /* Size and inuse bits. */
  struct malloc_chunk *fd;         /* double links -- used only if free. */
  struct malloc_chunk *bk;
};

typedef struct malloc_chunk  mchunk;
typedef struct malloc_chunk *mchunkptr;
typedef struct malloc_chunk *sbinptr;  /* The type of bins of chunks */
typedef size_t bindex_t;               /* Described below */
typedef unsigned int binmap_t;         /* Described below */
typedef unsigned int flag_t;           /* The type of various bit flag sets */

/* ------------------- Chunks sizes and alignments ----------------------- */

#define MCHUNK_SIZE		(sizeof(mchunk))

#define CHUNK_OVERHEAD		(SIZE_T_SIZE)

/* Direct chunks need a second word of overhead ... */
#define DIRECT_CHUNK_OVERHEAD	(TWO_SIZE_T_SIZES)
/* ... and additional padding for fake next-chunk at foot */
#define DIRECT_FOOT_PAD		(FOUR_SIZE_T_SIZES)

/* The smallest size we can malloc is an aligned minimal chunk */
#define MIN_CHUNK_SIZE\
  ((MCHUNK_SIZE + CHUNK_ALIGN_MASK) & ~CHUNK_ALIGN_MASK)

/* conversion from malloc headers to user pointers, and back */
#define chunk2mem(p)		((void *)((char *)(p) + TWO_SIZE_T_SIZES))
#define mem2chunk(mem)		((mchunkptr)((char *)(mem) - TWO_SIZE_T_SIZES))
/* chunk associated with aligned address A */
#define align_as_chunk(A)	(mchunkptr)((A) + align_offset(chunk2mem(A)))

/* Bounds on request (not chunk) sizes. */
#define MAX_REQUEST		((~MIN_CHUNK_SIZE+1) << 2)
#define MIN_REQUEST		(MIN_CHUNK_SIZE - CHUNK_OVERHEAD - SIZE_T_ONE)

/* pad request bytes into a usable size */
#define pad_request(req) \
   (((req) + CHUNK_OVERHEAD + CHUNK_ALIGN_MASK) & ~CHUNK_ALIGN_MASK)

/* pad request, checking for minimum (but not maximum) */
#define request2size(req) \
  (((req) < MIN_REQUEST)? MIN_CHUNK_SIZE : pad_request(req))

/* ------------------ Operations on head and foot fields ----------------- */

#define PINUSE_BIT		(SIZE_T_ONE)
#define CINUSE_BIT		(SIZE_T_TWO)
#define INUSE_BITS		(PINUSE_BIT|CINUSE_BIT)

/* Head value for fenceposts */
#define FENCEPOST_HEAD		(INUSE_BITS|SIZE_T_SIZE)

/* extraction of fields from head words */
#define cinuse(p)		((p)->head & CINUSE_BIT)
#define pinuse(p)		((p)->head & PINUSE_BIT)
#define chunksize(p)		((p)->head & ~(INUSE_BITS))

#define clear_pinuse(p)		((p)->head &= ~PINUSE_BIT)
#define clear_cinuse(p)		((p)->head &= ~CINUSE_BIT)

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

/* Ptr to next or previous physical malloc_chunk. */
#define next_chunk(p)	((mchunkptr)(((char *)(p)) + ((p)->head & ~INUSE_BITS)))
#define prev_chunk(p)	((mchunkptr)(((char *)(p)) - ((p)->prev_foot) ))

/* extract next chunk's pinuse bit */
#define next_pinuse(p)	((next_chunk(p)->head) & PINUSE_BIT)

/* Get/set size at footer */
#define get_foot(p, s)	(((mchunkptr)((char *)(p) + (s)))->prev_foot)
#define set_foot(p, s)	(((mchunkptr)((char *)(p) + (s)))->prev_foot = (s))

/* Set size, pinuse bit, and foot */
#define set_size_and_pinuse_of_free_chunk(p, s)\
  ((p)->head = (s|PINUSE_BIT), set_foot(p, s))

/* Set size, pinuse bit, foot, and clear next pinuse */
#define set_free_with_pinuse(p, s, n)\
  (clear_pinuse(n), set_size_and_pinuse_of_free_chunk(p, s))

#define is_direct(p)\
  (!((p)->head & PINUSE_BIT) && ((p)->prev_foot & IS_DIRECT_BIT))

/* Get the internal overhead associated with chunk p */
#define overhead_for(p)\
 (is_direct(p)? DIRECT_CHUNK_OVERHEAD : CHUNK_OVERHEAD)

/* ---------------------- Overlaid data structures ----------------------- */

struct malloc_tree_chunk {
  /* The first four fields must be compatible with malloc_chunk */
  size_t                    prev_foot;
  size_t                    head;
  struct malloc_tree_chunk *fd;
  struct malloc_tree_chunk *bk;

  struct malloc_tree_chunk *child[2];
  struct malloc_tree_chunk *parent;
  bindex_t                  index;
};

typedef struct malloc_tree_chunk  tchunk;
typedef struct malloc_tree_chunk *tchunkptr;
typedef struct malloc_tree_chunk *tbinptr; /* The type of bins of trees */

/* A little helper macro for trees */
#define leftmost_child(t) ((t)->child[0] != 0? (t)->child[0] : (t)->child[1])

/* ----------------------------- Segments -------------------------------- */

struct malloc_segment {
  char        *base;             /* base address */
  size_t       size;             /* allocated size */
  struct malloc_segment *next;   /* ptr to next segment */
};

typedef struct malloc_segment  msegment;
typedef struct malloc_segment *msegmentptr;

/* ---------------------------- malloc_state ----------------------------- */

/* Bin types, widths and sizes */
#define NSMALLBINS		(32U)
#define NTREEBINS		(32U)
#define SMALLBIN_SHIFT		(3U)
#define SMALLBIN_WIDTH		(SIZE_T_ONE << SMALLBIN_SHIFT)
#define TREEBIN_SHIFT		(8U)
#define MIN_LARGE_SIZE		(SIZE_T_ONE << TREEBIN_SHIFT)
#define MAX_SMALL_SIZE		(MIN_LARGE_SIZE - SIZE_T_ONE)
#define MAX_SMALL_REQUEST  (MAX_SMALL_SIZE - CHUNK_ALIGN_MASK - CHUNK_OVERHEAD)

struct malloc_state {
  binmap_t   smallmap;
  binmap_t   treemap;
  size_t     dvsize;
  size_t     topsize;
  mchunkptr  dv;
  mchunkptr  top;
  size_t     trim_check;
  size_t     release_checks;
  mchunkptr  smallbins[(NSMALLBINS+1)*2];
  tbinptr    treebins[NTREEBINS];
  msegment   seg;
};

typedef struct malloc_state *mstate;

#define is_initialized(M)	((M)->top != 0)

/* -------------------------- system alloc setup ------------------------- */

/* page-align a size */
#define page_align(S)\
 (((S) + (LJ_PAGESIZE - SIZE_T_ONE)) & ~(LJ_PAGESIZE - SIZE_T_ONE))

/* granularity-align a size */
#define granularity_align(S)\
  (((S) + (DEFAULT_GRANULARITY - SIZE_T_ONE))\
   & ~(DEFAULT_GRANULARITY - SIZE_T_ONE))

#if LJ_TARGET_WINDOWS
#define mmap_align(S)	granularity_align(S)
#else
#define mmap_align(S)	page_align(S)
#endif

/*  True if segment S holds address A */
#define segment_holds(S, A)\
  ((char *)(A) >= S->base && (char *)(A) < S->base + S->size)

/* Return segment holding given address */
static msegmentptr segment_holding(mstate m, char *addr)
{
  msegmentptr sp = &m->seg;
  for (;;) {
    if (addr >= sp->base && addr < sp->base + sp->size)
      return sp;
    if ((sp = sp->next) == 0)
      return 0;
  }
}

/* Return true if segment contains a segment link */
static int has_segment_link(mstate m, msegmentptr ss)
{
  msegmentptr sp = &m->seg;
  for (;;) {
    if ((char *)sp >= ss->base && (char *)sp < ss->base + ss->size)
      return 1;
    if ((sp = sp->next) == 0)
      return 0;
  }
}

/*
  TOP_FOOT_SIZE is padding at the end of a segment, including space
  that may be needed to place segment records and fenceposts when new
  noncontiguous segments are added.
*/
#define TOP_FOOT_SIZE\
  (align_offset(chunk2mem(0))+pad_request(sizeof(struct malloc_segment))+MIN_CHUNK_SIZE)

/* ---------------------------- Indexing Bins ---------------------------- */

#define is_small(s)		(((s) >> SMALLBIN_SHIFT) < NSMALLBINS)
#define small_index(s)		((s)  >> SMALLBIN_SHIFT)
#define small_index2size(i)	((i)  << SMALLBIN_SHIFT)
#define MIN_SMALL_INDEX		(small_index(MIN_CHUNK_SIZE))

/* addressing by index. See above about smallbin repositioning */
#define smallbin_at(M, i)	((sbinptr)((char *)&((M)->smallbins[(i)<<1])))
#define treebin_at(M,i)		(&((M)->treebins[i]))

/* assign tree index for size S to variable I */
#define compute_tree_index(S, I)\
{\
  unsigned int X = (unsigned int)(S >> TREEBIN_SHIFT);\
  if (X == 0) {\
    I = 0;\
  } else if (X > 0xFFFF) {\
    I = NTREEBINS-1;\
  } else {\
    unsigned int K = lj_fls(X);\
    I =  (bindex_t)((K << 1) + ((S >> (K + (TREEBIN_SHIFT-1)) & 1)));\
  }\
}

/* Bit representing maximum resolved size in a treebin at i */
#define bit_for_tree_index(i) \
   (i == NTREEBINS-1)? (SIZE_T_BITSIZE-1) : (((i) >> 1) + TREEBIN_SHIFT - 2)

/* Shift placing maximum resolved bit in a treebin at i as sign bit */
#define leftshift_for_tree_index(i) \
   ((i == NTREEBINS-1)? 0 : \
    ((SIZE_T_BITSIZE-SIZE_T_ONE) - (((i) >> 1) + TREEBIN_SHIFT - 2)))

/* The size of the smallest chunk held in bin with index i */
#define minsize_for_tree_index(i) \
   ((SIZE_T_ONE << (((i) >> 1) + TREEBIN_SHIFT)) |  \
   (((size_t)((i) & SIZE_T_ONE)) << (((i) >> 1) + TREEBIN_SHIFT - 1)))

/* ------------------------ Operations on bin maps ----------------------- */

/* bit corresponding to given index */
#define idx2bit(i)		((binmap_t)(1) << (i))

/* Mark/Clear bits with given index */
#define mark_smallmap(M,i)	((M)->smallmap |=  idx2bit(i))
#define clear_smallmap(M,i)	((M)->smallmap &= ~idx2bit(i))
#define smallmap_is_marked(M,i)	((M)->smallmap &   idx2bit(i))

#define mark_treemap(M,i)	((M)->treemap  |=  idx2bit(i))
#define clear_treemap(M,i)	((M)->treemap  &= ~idx2bit(i))
#define treemap_is_marked(M,i)	((M)->treemap  &   idx2bit(i))

/* mask with all bits to left of least bit of x on */
#define left_bits(x)		((x<<1) | (~(x<<1)+1))

/* Set cinuse bit and pinuse bit of next chunk */
#define set_inuse(M,p,s)\
  ((p)->head = (((p)->head & PINUSE_BIT)|s|CINUSE_BIT),\
  ((mchunkptr)(((char *)(p)) + (s)))->head |= PINUSE_BIT)

/* Set cinuse and pinuse of this chunk and pinuse of next chunk */
#define set_inuse_and_pinuse(M,p,s)\
  ((p)->head = (s|PINUSE_BIT|CINUSE_BIT),\
  ((mchunkptr)(((char *)(p)) + (s)))->head |= PINUSE_BIT)

/* Set size, cinuse and pinuse bit of this chunk */
#define set_size_and_pinuse_of_inuse_chunk(M, p, s)\
  ((p)->head = (s|PINUSE_BIT|CINUSE_BIT))

/* ----------------------- Operations on smallbins ----------------------- */

/* Link a free chunk into a smallbin  */
#define insert_small_chunk(M, P, S) {\
  bindex_t I = small_index(S);\
  mchunkptr B = smallbin_at(M, I);\
  mchunkptr F = B;\
  if (!smallmap_is_marked(M, I))\
    mark_smallmap(M, I);\
  else\
    F = B->fd;\
  B->fd = P;\
  F->bk = P;\
  P->fd = F;\
  P->bk = B;\
}

/* Unlink a chunk from a smallbin  */
#define unlink_small_chunk(M, P, S) {\
  mchunkptr F = P->fd;\
  mchunkptr B = P->bk;\
  bindex_t I = small_index(S);\
  if (F == B) {\
    clear_smallmap(M, I);\
  } else {\
    F->bk = B;\
    B->fd = F;\
  }\
}

/* Unlink the first chunk from a smallbin */
#define unlink_first_small_chunk(M, B, P, I) {\
  mchunkptr F = P->fd;\
  if (B == F) {\
    clear_smallmap(M, I);\
  } else {\
    B->fd = F;\
    F->bk = B;\
  }\
}

/* Replace dv node, binning the old one */
/* Used only when dvsize known to be small */
#define replace_dv(M, P, S) {\
  size_t DVS = M->dvsize;\
  if (DVS != 0) {\
    mchunkptr DV = M->dv;\
    insert_small_chunk(M, DV, DVS);\
  }\
  M->dvsize = S;\
  M->dv = P;\
}

/* ------------------------- Operations on trees ------------------------- */

/* Insert chunk into tree */
#define insert_large_chunk(M, X, S) {\
  tbinptr *H;\
  bindex_t I;\
  compute_tree_index(S, I);\
  H = treebin_at(M, I);\
  X->index = I;\
  X->child[0] = X->child[1] = 0;\
  if (!treemap_is_marked(M, I)) {\
    mark_treemap(M, I);\
    *H = X;\
    X->parent = (tchunkptr)H;\
    X->fd = X->bk = X;\
  } else {\
    tchunkptr T = *H;\
    size_t K = S << leftshift_for_tree_index(I);\
    for (;;) {\
      if (chunksize(T) != S) {\
	tchunkptr *C = &(T->child[(K >> (SIZE_T_BITSIZE-SIZE_T_ONE)) & 1]);\
	K <<= 1;\
	if (*C != 0) {\
	  T = *C;\
	} else {\
	  *C = X;\
	  X->parent = T;\
	  X->fd = X->bk = X;\
	  break;\
	}\
      } else {\
	tchunkptr F = T->fd;\
	T->fd = F->bk = X;\
	X->fd = F;\
	X->bk = T;\
	X->parent = 0;\
	break;\
      }\
    }\
  }\
}

#define unlink_large_chunk(M, X) {\
  tchunkptr XP = X->parent;\
  tchunkptr R;\
  if (X->bk != X) {\
    tchunkptr F = X->fd;\
    R = X->bk;\
    F->bk = R;\
    R->fd = F;\
  } else {\
    tchunkptr *RP;\
    if (((R = *(RP = &(X->child[1]))) != 0) ||\
	((R = *(RP = &(X->child[0]))) != 0)) {\
      tchunkptr *CP;\
      while ((*(CP = &(R->child[1])) != 0) ||\
	     (*(CP = &(R->child[0])) != 0)) {\
	R = *(RP = CP);\
      }\
      *RP = 0;\
    }\
  }\
  if (XP != 0) {\
    tbinptr *H = treebin_at(M, X->index);\
    if (X == *H) {\
      if ((*H = R) == 0) \
	clear_treemap(M, X->index);\
    } else {\
      if (XP->child[0] == X) \
	XP->child[0] = R;\
      else \
	XP->child[1] = R;\
    }\
    if (R != 0) {\
      tchunkptr C0, C1;\
      R->parent = XP;\
      if ((C0 = X->child[0]) != 0) {\
	R->child[0] = C0;\
	C0->parent = R;\
      }\
      if ((C1 = X->child[1]) != 0) {\
	R->child[1] = C1;\
	C1->parent = R;\
      }\
    }\
  }\
}

/* Relays to large vs small bin operations */

#define insert_chunk(M, P, S)\
  if (is_small(S)) { insert_small_chunk(M, P, S)\
  } else { tchunkptr TP = (tchunkptr)(P); insert_large_chunk(M, TP, S); }

#define unlink_chunk(M, P, S)\
  if (is_small(S)) { unlink_small_chunk(M, P, S)\
  } else { tchunkptr TP = (tchunkptr)(P); unlink_large_chunk(M, TP); }

/* -----------------------  Direct-mmapping chunks ----------------------- */

static void *direct_alloc(size_t nb)
{
  size_t mmsize = mmap_align(nb + SIX_SIZE_T_SIZES + CHUNK_ALIGN_MASK);
  if (LJ_LIKELY(mmsize > nb)) {     /* Check for wrap around 0 */
    char *mm = (char *)(DIRECT_MMAP(mmsize));
    if (mm != CMFAIL) {
      size_t offset = align_offset(chunk2mem(mm));
      size_t psize = mmsize - offset - DIRECT_FOOT_PAD;
      mchunkptr p = (mchunkptr)(mm + offset);
      p->prev_foot = offset | IS_DIRECT_BIT;
      p->head = psize|CINUSE_BIT;
      chunk_plus_offset(p, psize)->head = FENCEPOST_HEAD;
      chunk_plus_offset(p, psize+SIZE_T_SIZE)->head = 0;
      return chunk2mem(p);
    }
  }
  return NULL;
}

static mchunkptr direct_resize(mchunkptr oldp, size_t nb)
{
  size_t oldsize = chunksize(oldp);
  if (is_small(nb)) /* Can't shrink direct regions below small size */
    return NULL;
  /* Keep old chunk if big enough but not too big */
  if (oldsize >= nb + SIZE_T_SIZE &&
      (oldsize - nb) <= (DEFAULT_GRANULARITY >> 1)) {
    return oldp;
  } else {
    size_t offset = oldp->prev_foot & ~IS_DIRECT_BIT;
    size_t oldmmsize = oldsize + offset + DIRECT_FOOT_PAD;
    size_t newmmsize = mmap_align(nb + SIX_SIZE_T_SIZES + CHUNK_ALIGN_MASK);
    char *cp = (char *)CALL_MREMAP((char *)oldp - offset,
				   oldmmsize, newmmsize, CALL_MREMAP_MV);
    if (cp != CMFAIL) {
      mchunkptr newp = (mchunkptr)(cp + offset);
      size_t psize = newmmsize - offset - DIRECT_FOOT_PAD;
      newp->head = psize|CINUSE_BIT;
      chunk_plus_offset(newp, psize)->head = FENCEPOST_HEAD;
      chunk_plus_offset(newp, psize+SIZE_T_SIZE)->head = 0;
      return newp;
    }
  }
  return NULL;
}

/* -------------------------- mspace management -------------------------- */

/* Initialize top chunk and its size */
static void init_top(mstate m, mchunkptr p, size_t psize)
{
  /* Ensure alignment */
  size_t offset = align_offset(chunk2mem(p));
  p = (mchunkptr)((char *)p + offset);
  psize -= offset;

  m->top = p;
  m->topsize = psize;
  p->head = psize | PINUSE_BIT;
  /* set size of fake trailing chunk holding overhead space only once */
  chunk_plus_offset(p, psize)->head = TOP_FOOT_SIZE;
  m->trim_check = DEFAULT_TRIM_THRESHOLD; /* reset on each update */
}

/* Initialize bins for a new mstate that is otherwise zeroed out */
static void init_bins(mstate m)
{
  /* Establish circular links for smallbins */
  bindex_t i;
  for (i = 0; i < NSMALLBINS; i++) {
    sbinptr bin = smallbin_at(m,i);
    bin->fd = bin->bk = bin;
  }
}

/* Allocate chunk and prepend remainder with chunk in successor base. */
static void *prepend_alloc(mstate m, char *newbase, char *oldbase, size_t nb)
{
  mchunkptr p = align_as_chunk(newbase);
  mchunkptr oldfirst = align_as_chunk(oldbase);
  size_t psize = (size_t)((char *)oldfirst - (char *)p);
  mchunkptr q = chunk_plus_offset(p, nb);
  size_t qsize = psize - nb;
  set_size_and_pinuse_of_inuse_chunk(m, p, nb);

  /* consolidate remainder with first chunk of old base */
  if (oldfirst == m->top) {
    size_t tsize = m->topsize += qsize;
    m->top = q;
    q->head = tsize | PINUSE_BIT;
  } else if (oldfirst == m->dv) {
    size_t dsize = m->dvsize += qsize;
    m->dv = q;
    set_size_and_pinuse_of_free_chunk(q, dsize);
  } else {
    if (!cinuse(oldfirst)) {
      size_t nsize = chunksize(oldfirst);
      unlink_chunk(m, oldfirst, nsize);
      oldfirst = chunk_plus_offset(oldfirst, nsize);
      qsize += nsize;
    }
    set_free_with_pinuse(q, qsize, oldfirst);
    insert_chunk(m, q, qsize);
  }

  return chunk2mem(p);
}

/* Add a segment to hold a new noncontiguous region */
static void add_segment(mstate m, char *tbase, size_t tsize)
{
  /* Determine locations and sizes of segment, fenceposts, old top */
  char *old_top = (char *)m->top;
  msegmentptr oldsp = segment_holding(m, old_top);
  char *old_end = oldsp->base + oldsp->size;
  size_t ssize = pad_request(sizeof(struct malloc_segment));
  char *rawsp = old_end - (ssize + FOUR_SIZE_T_SIZES + CHUNK_ALIGN_MASK);
  size_t offset = align_offset(chunk2mem(rawsp));
  char *asp = rawsp + offset;
  char *csp = (asp < (old_top + MIN_CHUNK_SIZE))? old_top : asp;
  mchunkptr sp = (mchunkptr)csp;
  msegmentptr ss = (msegmentptr)(chunk2mem(sp));
  mchunkptr tnext = chunk_plus_offset(sp, ssize);
  mchunkptr p = tnext;

  /* reset top to new space */
  init_top(m, (mchunkptr)tbase, tsize - TOP_FOOT_SIZE);

  /* Set up segment record */
  set_size_and_pinuse_of_inuse_chunk(m, sp, ssize);
  *ss = m->seg; /* Push current record */
  m->seg.base = tbase;
  m->seg.size = tsize;
  m->seg.next = ss;

  /* Insert trailing fenceposts */
  for (;;) {
    mchunkptr nextp = chunk_plus_offset(p, SIZE_T_SIZE);
    p->head = FENCEPOST_HEAD;
    if ((char *)(&(nextp->head)) < old_end)
      p = nextp;
    else
      break;
  }

  /* Insert the rest of old top into a bin as an ordinary free chunk */
  if (csp != old_top) {
    mchunkptr q = (mchunkptr)old_top;
    size_t psize = (size_t)(csp - old_top);
    mchunkptr tn = chunk_plus_offset(q, psize);
    set_free_with_pinuse(q, psize, tn);
    insert_chunk(m, q, psize);
  }
}

/* -------------------------- System allocation -------------------------- */

static void *alloc_sys(mstate m, size_t nb)
{
  char *tbase = CMFAIL;
  size_t tsize = 0;

  /* Directly map large chunks */
  if (LJ_UNLIKELY(nb >= DEFAULT_MMAP_THRESHOLD)) {
    void *mem = direct_alloc(nb);
    if (mem != 0)
      return mem;
  }

  {
    size_t req = nb + TOP_FOOT_SIZE + SIZE_T_ONE;
    size_t rsize = granularity_align(req);
    if (LJ_LIKELY(rsize > nb)) { /* Fail if wraps around zero */
      char *mp = (char *)(CALL_MMAP(rsize));
      if (mp != CMFAIL) {
	tbase = mp;
	tsize = rsize;
      }
    }
  }

  if (tbase != CMFAIL) {
    msegmentptr sp = &m->seg;
    /* Try to merge with an existing segment */
    while (sp != 0 && tbase != sp->base + sp->size)
      sp = sp->next;
    if (sp != 0 && segment_holds(sp, m->top)) { /* append */
      sp->size += tsize;
      init_top(m, m->top, m->topsize + tsize);
    } else {
      sp = &m->seg;
      while (sp != 0 && sp->base != tbase + tsize)
	sp = sp->next;
      if (sp != 0) {
	char *oldbase = sp->base;
	sp->base = tbase;
	sp->size += tsize;
	return prepend_alloc(m, tbase, oldbase, nb);
      } else {
	add_segment(m, tbase, tsize);
      }
    }

    if (nb < m->topsize) { /* Allocate from new or extended top space */
      size_t rsize = m->topsize -= nb;
      mchunkptr p = m->top;
      mchunkptr r = m->top = chunk_plus_offset(p, nb);
      r->head = rsize | PINUSE_BIT;
      set_size_and_pinuse_of_inuse_chunk(m, p, nb);
      return chunk2mem(p);
    }
  }

  return NULL;
}

/* -----------------------  system deallocation -------------------------- */

/* Unmap and unlink any mmapped segments that don't contain used chunks */
static size_t release_unused_segments(mstate m)
{
  size_t released = 0;
  size_t nsegs = 0;
  msegmentptr pred = &m->seg;
  msegmentptr sp = pred->next;
  while (sp != 0) {
    char *base = sp->base;
    size_t size = sp->size;
    msegmentptr next = sp->next;
    nsegs++;
    {
      mchunkptr p = align_as_chunk(base);
      size_t psize = chunksize(p);
      /* Can unmap if first chunk holds entire segment and not pinned */
      if (!cinuse(p) && (char *)p + psize >= base + size - TOP_FOOT_SIZE) {
	tchunkptr tp = (tchunkptr)p;
	if (p == m->dv) {
	  m->dv = 0;
	  m->dvsize = 0;
	} else {
	  unlink_large_chunk(m, tp);
	}
	if (CALL_MUNMAP(base, size) == 0) {
	  released += size;
	  /* unlink obsoleted record */
	  sp = pred;
	  sp->next = next;
	} else { /* back out if cannot unmap */
	  insert_large_chunk(m, tp, psize);
	}
      }
    }
    pred = sp;
    sp = next;
  }
  /* Reset check counter */
  m->release_checks = nsegs > MAX_RELEASE_CHECK_RATE ?
		      nsegs : MAX_RELEASE_CHECK_RATE;
  return released;
}

static int alloc_trim(mstate m, size_t pad)
{
  size_t released = 0;
  if (pad < MAX_REQUEST && is_initialized(m)) {
    pad += TOP_FOOT_SIZE; /* ensure enough room for segment overhead */

    if (m->topsize > pad) {
      /* Shrink top space in granularity-size units, keeping at least one */
      size_t unit = DEFAULT_GRANULARITY;
      size_t extra = ((m->topsize - pad + (unit - SIZE_T_ONE)) / unit -
		      SIZE_T_ONE) * unit;
      msegmentptr sp = segment_holding(m, (char *)m->top);

      if (sp->size >= extra &&
	  !has_segment_link(m, sp)) { /* can't shrink if pinned */
	size_t newsize = sp->size - extra;
	/* Prefer mremap, fall back to munmap */
	if ((CALL_MREMAP(sp->base, sp->size, newsize, CALL_MREMAP_NOMOVE) != MFAIL) ||
	    (CALL_MUNMAP(sp->base + newsize, extra) == 0)) {
	  released = extra;
	}
      }

      if (released != 0) {
	sp->size -= released;
	init_top(m, m->top, m->topsize - released);
      }
    }

    /* Unmap any unused mmapped segments */
    released += release_unused_segments(m);

    /* On failure, disable autotrim to avoid repeated failed future calls */
    if (released == 0 && m->topsize > m->trim_check)
      m->trim_check = MAX_SIZE_T;
  }

  return (released != 0)? 1 : 0;
}

/* ---------------------------- malloc support --------------------------- */

/* allocate a large request from the best fitting chunk in a treebin */
static void *tmalloc_large(mstate m, size_t nb)
{
  tchunkptr v = 0;
  size_t rsize = ~nb+1; /* Unsigned negation */
  tchunkptr t;
  bindex_t idx;
  compute_tree_index(nb, idx);

  if ((t = *treebin_at(m, idx)) != 0) {
    /* Traverse tree for this bin looking for node with size == nb */
    size_t sizebits = nb << leftshift_for_tree_index(idx);
    tchunkptr rst = 0;  /* The deepest untaken right subtree */
    for (;;) {
      tchunkptr rt;
      size_t trem = chunksize(t) - nb;
      if (trem < rsize) {
	v = t;
	if ((rsize = trem) == 0)
	  break;
      }
      rt = t->child[1];
      t = t->child[(sizebits >> (SIZE_T_BITSIZE-SIZE_T_ONE)) & 1];
      if (rt != 0 && rt != t)
	rst = rt;
      if (t == 0) {
	t = rst; /* set t to least subtree holding sizes > nb */
	break;
      }
      sizebits <<= 1;
    }
  }

  if (t == 0 && v == 0) { /* set t to root of next non-empty treebin */
    binmap_t leftbits = left_bits(idx2bit(idx)) & m->treemap;
    if (leftbits != 0)
      t = *treebin_at(m, lj_ffs(leftbits));
  }

  while (t != 0) { /* find smallest of tree or subtree */
    size_t trem = chunksize(t) - nb;
    if (trem < rsize) {
      rsize = trem;
      v = t;
    }
    t = leftmost_child(t);
  }

  /*  If dv is a better fit, return NULL so malloc will use it */
  if (v != 0 && rsize < (size_t)(m->dvsize - nb)) {
    mchunkptr r = chunk_plus_offset(v, nb);
    unlink_large_chunk(m, v);
    if (rsize < MIN_CHUNK_SIZE) {
      set_inuse_and_pinuse(m, v, (rsize + nb));
    } else {
      set_size_and_pinuse_of_inuse_chunk(m, v, nb);
      set_size_and_pinuse_of_free_chunk(r, rsize);
      insert_chunk(m, r, rsize);
    }
    return chunk2mem(v);
  }
  return NULL;
}

/* allocate a small request from the best fitting chunk in a treebin */
static void *tmalloc_small(mstate m, size_t nb)
{
  tchunkptr t, v;
  mchunkptr r;
  size_t rsize;
  bindex_t i = lj_ffs(m->treemap);

  v = t = *treebin_at(m, i);
  rsize = chunksize(t) - nb;

  while ((t = leftmost_child(t)) != 0) {
    size_t trem = chunksize(t) - nb;
    if (trem < rsize) {
      rsize = trem;
      v = t;
    }
  }

  r = chunk_plus_offset(v, nb);
  unlink_large_chunk(m, v);
  if (rsize < MIN_CHUNK_SIZE) {
    set_inuse_and_pinuse(m, v, (rsize + nb));
  } else {
    set_size_and_pinuse_of_inuse_chunk(m, v, nb);
    set_size_and_pinuse_of_free_chunk(r, rsize);
    replace_dv(m, r, rsize);
  }
  return chunk2mem(v);
}

/* ----------------------------------------------------------------------- */

void *lj_alloc_create(void)
{
  size_t tsize = DEFAULT_GRANULARITY;
  char *tbase;
  INIT_MMAP();
  tbase = (char *)(CALL_MMAP(tsize));
  if (tbase != CMFAIL) {
    size_t msize = pad_request(sizeof(struct malloc_state));
    mchunkptr mn;
    mchunkptr msp = align_as_chunk(tbase);
    mstate m = (mstate)(chunk2mem(msp));
    memset(m, 0, msize);
    msp->head = (msize|PINUSE_BIT|CINUSE_BIT);
    m->seg.base = tbase;
    m->seg.size = tsize;
    m->release_checks = MAX_RELEASE_CHECK_RATE;
    init_bins(m);
    mn = next_chunk(mem2chunk(m));
    init_top(m, mn, (size_t)((tbase + tsize) - (char *)mn) - TOP_FOOT_SIZE);
    return m;
  }
  return NULL;
}

void lj_alloc_destroy(void *msp)
{
  mstate ms = (mstate)msp;
  msegmentptr sp = &ms->seg;
  while (sp != 0) {
    char *base = sp->base;
    size_t size = sp->size;
    sp = sp->next;
    CALL_MUNMAP(base, size);
  }
}

static LJ_NOINLINE void *lj_alloc_malloc(void *msp, size_t nsize)
{
  mstate ms = (mstate)msp;
  void *mem;
  size_t nb;
  if (nsize <= MAX_SMALL_REQUEST) {
    bindex_t idx;
    binmap_t smallbits;
    nb = (nsize < MIN_REQUEST)? MIN_CHUNK_SIZE : pad_request(nsize);
    idx = small_index(nb);
    smallbits = ms->smallmap >> idx;

    if ((smallbits & 0x3U) != 0) { /* Remainderless fit to a smallbin. */
      mchunkptr b, p;
      idx += ~smallbits & 1;       /* Uses next bin if idx empty */
      b = smallbin_at(ms, idx);
      p = b->fd;
      unlink_first_small_chunk(ms, b, p, idx);
      set_inuse_and_pinuse(ms, p, small_index2size(idx));
      mem = chunk2mem(p);
      return mem;
    } else if (nb > ms->dvsize) {
      if (smallbits != 0) { /* Use chunk in next nonempty smallbin */
	mchunkptr b, p, r;
	size_t rsize;
	binmap_t leftbits = (smallbits << idx) & left_bits(idx2bit(idx));
	bindex_t i = lj_ffs(leftbits);
	b = smallbin_at(ms, i);
	p = b->fd;
	unlink_first_small_chunk(ms, b, p, i);
	rsize = small_index2size(i) - nb;
	/* Fit here cannot be remainderless if 4byte sizes */
	if (SIZE_T_SIZE != 4 && rsize < MIN_CHUNK_SIZE) {
	  set_inuse_and_pinuse(ms, p, small_index2size(i));
	} else {
	  set_size_and_pinuse_of_inuse_chunk(ms, p, nb);
	  r = chunk_plus_offset(p, nb);
	  set_size_and_pinuse_of_free_chunk(r, rsize);
	  replace_dv(ms, r, rsize);
	}
	mem = chunk2mem(p);
	return mem;
      } else if (ms->treemap != 0 && (mem = tmalloc_small(ms, nb)) != 0) {
	return mem;
      }
    }
  } else if (nsize >= MAX_REQUEST) {
    nb = MAX_SIZE_T; /* Too big to allocate. Force failure (in sys alloc) */
  } else {
    nb = pad_request(nsize);
    if (ms->treemap != 0 && (mem = tmalloc_large(ms, nb)) != 0) {
      return mem;
    }
  }

  if (nb <= ms->dvsize) {
    size_t rsize = ms->dvsize - nb;
    mchunkptr p = ms->dv;
    if (rsize >= MIN_CHUNK_SIZE) { /* split dv */
      mchunkptr r = ms->dv = chunk_plus_offset(p, nb);
      ms->dvsize = rsize;
      set_size_and_pinuse_of_free_chunk(r, rsize);
      set_size_and_pinuse_of_inuse_chunk(ms, p, nb);
    } else { /* exhaust dv */
      size_t dvs = ms->dvsize;
      ms->dvsize = 0;
      ms->dv = 0;
      set_inuse_and_pinuse(ms, p, dvs);
    }
    mem = chunk2mem(p);
    return mem;
  } else if (nb < ms->topsize) { /* Split top */
    size_t rsize = ms->topsize -= nb;
    mchunkptr p = ms->top;
    mchunkptr r = ms->top = chunk_plus_offset(p, nb);
    r->head = rsize | PINUSE_BIT;
    set_size_and_pinuse_of_inuse_chunk(ms, p, nb);
    mem = chunk2mem(p);
    return mem;
  }
  return alloc_sys(ms, nb);
}

static LJ_NOINLINE void *lj_alloc_free(void *msp, void *ptr)
{
  if (ptr != 0) {
    mchunkptr p = mem2chunk(ptr);
    mstate fm = (mstate)msp;
    size_t psize = chunksize(p);
    mchunkptr next = chunk_plus_offset(p, psize);
    if (!pinuse(p)) {
      size_t prevsize = p->prev_foot;
      if ((prevsize & IS_DIRECT_BIT) != 0) {
	prevsize &= ~IS_DIRECT_BIT;
	psize += prevsize + DIRECT_FOOT_PAD;
	CALL_MUNMAP((char *)p - prevsize, psize);
	return NULL;
      } else {
	mchunkptr prev = chunk_minus_offset(p, prevsize);
	psize += prevsize;
	p = prev;
	/* consolidate backward */
	if (p != fm->dv) {
	  unlink_chunk(fm, p, prevsize);
	} else if ((next->head & INUSE_BITS) == INUSE_BITS) {
	  fm->dvsize = psize;
	  set_free_with_pinuse(p, psize, next);
	  return NULL;
	}
      }
    }
    if (!cinuse(next)) {  /* consolidate forward */
      if (next == fm->top) {
	size_t tsize = fm->topsize += psize;
	fm->top = p;
	p->head = tsize | PINUSE_BIT;
	if (p == fm->dv) {
	  fm->dv = 0;
	  fm->dvsize = 0;
	}
	if (tsize > fm->trim_check)
	  alloc_trim(fm, 0);
	return NULL;
      } else if (next == fm->dv) {
	size_t dsize = fm->dvsize += psize;
	fm->dv = p;
	set_size_and_pinuse_of_free_chunk(p, dsize);
	return NULL;
      } else {
	size_t nsize = chunksize(next);
	psize += nsize;
	unlink_chunk(fm, next, nsize);
	set_size_and_pinuse_of_free_chunk(p, psize);
	if (p == fm->dv) {
	  fm->dvsize = psize;
	  return NULL;
	}
      }
    } else {
      set_free_with_pinuse(p, psize, next);
    }

    if (is_small(psize)) {
      insert_small_chunk(fm, p, psize);
    } else {
      tchunkptr tp = (tchunkptr)p;
      insert_large_chunk(fm, tp, psize);
      if (--fm->release_checks == 0)
	release_unused_segments(fm);
    }
  }
  return NULL;
}

static LJ_NOINLINE void *lj_alloc_realloc(void *msp, void *ptr, size_t nsize)
{
  if (nsize >= MAX_REQUEST) {
    return NULL;
  } else {
    mstate m = (mstate)msp;
    mchunkptr oldp = mem2chunk(ptr);
    size_t oldsize = chunksize(oldp);
    mchunkptr next = chunk_plus_offset(oldp, oldsize);
    mchunkptr newp = 0;
    size_t nb = request2size(nsize);

    /* Try to either shrink or extend into top. Else malloc-copy-free */
    if (is_direct(oldp)) {
      newp = direct_resize(oldp, nb);  /* this may return NULL. */
    } else if (oldsize >= nb) { /* already big enough */
      size_t rsize = oldsize - nb;
      newp = oldp;
      if (rsize >= MIN_CHUNK_SIZE) {
	mchunkptr rem = chunk_plus_offset(newp, nb);
	set_inuse(m, newp, nb);
	set_inuse(m, rem, rsize);
	lj_alloc_free(m, chunk2mem(rem));
      }
    } else if (next == m->top && oldsize + m->topsize > nb) {
      /* Expand into top */
      size_t newsize = oldsize + m->topsize;
      size_t newtopsize = newsize - nb;
      mchunkptr newtop = chunk_plus_offset(oldp, nb);
      set_inuse(m, oldp, nb);
      newtop->head = newtopsize |PINUSE_BIT;
      m->top = newtop;
      m->topsize = newtopsize;
      newp = oldp;
    }

    if (newp != 0) {
      return chunk2mem(newp);
    } else {
      void *newmem = lj_alloc_malloc(m, nsize);
      if (newmem != 0) {
	size_t oc = oldsize - overhead_for(oldp);
	memcpy(newmem, ptr, oc < nsize ? oc : nsize);
	lj_alloc_free(m, ptr);
      }
      return newmem;
    }
  }
}

void *lj_alloc_f(void *msp, void *ptr, size_t osize, size_t nsize)
{
  (void)osize;
  if (nsize == 0) {
    return lj_alloc_free(msp, ptr);
  } else if (ptr == NULL) {
    return lj_alloc_malloc(msp, nsize);
  } else {
    return lj_alloc_realloc(msp, ptr, nsize);
  }
}

#endif